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P07 LabNotesPt2 and Interference Lab

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					Experiment 9: THE TANGENT GALVANOMETER

PURPOSE:

       In this experiment we will measure the magnitude of the horizontal component of the
Earth's Magnetic field by the use of an instrument called a tangent galvanometer.


INTRODUCTION:

       A tangent galvanometer consists of a number of turns of copper wire wound on a hoop. At
the center of the hoop a compass is mounted. When a direct current flows through the wires, a
magnetic field is induced in the space surrounding the loops of wire. This magnetic flux is
designated by Bi . The strength of the magnetic field induced by the current at the center of the
loops of wire is given by Amperes law:

                                                             o N I
                                        Induced Bi =                .
                                                              2R

where o is the permeability of free space and has the value of 4 x 10-7 N/A2, N is the number
of turns of wire, I is the current through the wire, and R is the radius of the loop.
       When the wire loops of the tangent galvanometer are aligned with the magnetic field of the
Earth, and a current is sent through the wire loops, then the compass needle will align with the
vector sum of the field of the Earth and the induced field as shown in Figure 1.

                   Magnetic
                    North
                                               Bresultant
                           B of Earth                                        Compass Needle
                                                                             Direction

                                          



                                                                       Bi   (induced)




                                                   Fig. 1


       The horizontal component of the magnetic field of the Earth is easily calculated from the
following relation:


                                                              Bi
                                        B of Earth =               .
                                                             tan 




                                                    - 24 -
SUPPLIES & EQUIPMENT:

      Tangent galvanometer        Ammeter               Leads & connectors
      Reversing switch            Ruler                 Rheostat, 20 
      DC supply, 6 V              Plywood board


PROCEDURE:

1. Set up the apparatus on a board between tables as shown in Figure 2. Be sure to orient the
   loops exactly in the North-South direction. Orient the compass so that the needle is pointing
   to zero degrees.

       Rheostat

                  A                        Tangent
                             Reversing
                              Switch     Galvanometer                   5        10

                                                                         15 Turns


                                                         Binding posts configuration
             Fig. 2: Apparatus Wiring Diagram

2. Supply power to the 10-turns binding posts and adjust the rheostat until a deflection of 45 o is
   indicated on the compass. Reverse the current to obtain a 45 o deflection on the other side of
   the compass. Record the exact current for each deflection.

3. Sketch a vector diagram for the situation where there is a 45 o deflection. Calculate the
   magnitude of the horizontal component of the Earth's magnetic field. The SI unit for B is the
   Tesla (T). There are 104 gauss per Tesla.

4. Repeat steps 2 and 3 for a 63.5o deflection. What is the relationship between the Earth's field
   and the field of the loop for this case? Draw a vector diagram.

5. Repeat the entire procedure for the 15-turns binding posts. What conclusion can you draw
   about the magnetic field of the loop from this part of the experiment?




                                              - 25 -
DATA SHEET: The Tangent Galvanometer


Data and Calculations table for 45o deflection

                                           Current
  Number                                    (A)                     Binduced   BEarth
  Of Turns     Deflection                                             (T)       (T)
                              Right          Left         Average

                    o
    10            45


                    o
    15            45


Vector diagram for above case




Data and calculations table for 63.5o deflection

                                           Current
  Number                                    (A)                     Binduced   BEarth
  Of Turns     Deflection                                             (T)       (T)
                              Right          Left         Average

                        o
    10           63.5


                        o
    15           63.5


Vector diagram for above case




                                                 - 26 -
Experiment 10: CAPACITIVE & INDUCTIVE REACTANCE

PURPOSE:

       In this experiment we will study the effects of inductors and capacitors in a series
alternating current circuit. From the observation of these effects, the concepts of high pass and
low pass filters will be apparent.


INTRODUCTION:

       In an AC circuit containing resistance and either inductance or capacitance, the resistive
effect of these circuit elements is called the inductive reactance X L and capacitive reactance XC
respectively. These reactances are given theoretically by:

                            XL = 2 fL,               XC =     1 .           (Unit is the ohm.)
                                                              2fC

These impedances are proportional to the frequency at which the circuit is driven. Experimentally,
we can obtain a value for these reactances from the following equation:

                            XL = VL/I                 XC = VC/I

Since the voltages across the inductor and capacitor are out of phase with the voltage across the
resistor VR by 90o, it is necessary to add the voltages vectorially to obtain the voltage across
either the inductor or the capacitor:

                                    2          2
                            VL =   Vs        VR .    (where Vs = source voltage)

The current in the circuit is given by: I = VR/R


SUPPLIES & EQUIPMENT:

       AC generator              
       Frequency counter                                             f   V         BNC
       Digital voltmeter DVM, ACV 2-Volt range                                     Output
       Inductance coil, 10 mH
                                                                                       BNC
       Composition resistor, 470
               (yellow, violet, brown, silver)                                         2 Wires
       Ruler & French curve
       Decade capacitor box




                                                     - 27 -
PROCEDURE:

Part   A.   Inductive Reactance

1. Set up the apparatus as shown in Figure 1.

                                                   L




                         Vs                                      R = 470   VR
                               ~


                                                        Fig. 1

2. Set the function generator (Vs) to approximately 2 Volts and set the frequency to 1000 Hz.
   (Check Vs with the DVM set at ACV, 2V and check the frequency with the frequency counter.)

3. Record the source voltage and the voltage across the resistor on the data table.

                                  2            2
4. Determine        VL from VL = Vs          VR

                      I from   I = VR / R

                    XL from XL = VL / I

5. Repeat steps 2 through 4 for f = 1500 Hz to 4500 Hz in steps of 500 Hz.

6. Compare the experimental reactance with the theoretical reactance.

7. Plot XL versus frequency.


Part B: Capacitive Reactance

1. Repeat the above procedure only this time use a 0.5 F capacitor as the element instead of
   the inductor.




                                                       - 28 -
DATA SHEET: Capacitive and Inductive Reactance

Data and Calculations Table 1: Inductive Reactance.

                          Voltage        Voltage                      Inductive
Frequency    Source        Across        Across                      Reactance    Theoretical
     f      Voltage Vs   Resistor VR   Inductor VL    Current I          XL          XL         % difference
   (Hz)         (V)          (V)           (V)          (A)              ()         ()

  1500

  2000

  2500

  3000

  3500

  4000

  4500

Data Table 2, Capacitive Reactance

                          Voltage        Voltage                     Capacitive
Frequency    Source        Across        Across                      Reactance    Theoretical
     f      Voltage Vs   Resistor VR   Capacitor VC      Current I      XL           XC         % difference
   (Hz)         (V)          (V)           (V)             (A)          ()          ()

  1000

  1500

  2000

  2500

  3000

  3500

  4000

  4500




                                                - 29 -
Experiment 11: THE OSCILLOSCOPE
PURPOSE: a) Introduce the principles of operation
         b) Measure AC voltages and frequencies
         c) Observe Lissajous Figures

INTRODUCTION:
      The oscilloscope (shown schematically in Figure 1) is an essential instrument in the study
of AC signals and circuits.
                                                                Vertical Input

                                               Amplifier

                    Filament

 Synchronizing                                                             Electron Beam
    Voltage

                               Vo                        Amplifier

                     Generator                                 Switch

                                                                         Horizontal Input


                                           Fig. 1. The Oscilloscope


                  HITACHI   OSCILLOSCOPE
                                                           A         B

                                                           D                  E             C

                                                                               F

                                                           G                   H

              I                                                                  J
                                                                                            K
                               L           M                         N

              O                    P                       Q                   R


                                                           Fig. 2

A)   Power on/off and intensity                     J) Type of signal for channel 2.
B)   Horizontal position of both traces,            K) Channel trigger settings.
     pull switch for 10X horizontal                 L) Channel 1, vertical amplitude
C)   Trigger setting for channel 2.                 M) Chooses type of display for channels 1 & 2
D)   Beam focusing                                  N) Channel 2, vertical amplitude
E)   Time per screen division = 1 cm                O) Signal input for channel 1.
F)   Knob making time/division variable.            P) Vertical positioning of trace of channel 1.
G)   Screen scale illumination.                        Pull switch for 5X vertical.
H)   x-y setting for Lissajous Figures.             Q) Vertical positioning of trace of channel 2.
I)   Type of signal for channel 1.                  R) Signal input for channel 2.
                                                       Pull switch for 5X vertical.

                                                           - 30 -
SUPPLIES & EQUIPMENT:

      Hitachi dual trace oscilloscope V-550B                 1000  carbon resistor
      Function generator (F. G.) Simpson # 420               Test leads as needed
      Digital voltmeter Digetec, model 2180                  Frequency counter,
      Power outlet strip                                     Tenma, model # 72-460
      BNC to banana adaptor


PROCEDURE:

PART I: OSCILLOSCOPE SETUP

A. Adjustments to obtain trace:   1) Intensity -Low                knobs/lever: A,G
                                  2) Trigger    -Ext                            C
                                  3) Position -Center                           B, P, Q
                                  4) Coupling -AC                               I, J
                                  5) Focus      -Sharp                          D, G
                                  6) Sweep      -1 msec/cm                      E
                                  7) Deflection -1 V/cm                         L, N
   Refer to Figure 2.




PART II: MEASURING AN AC (SINE WAVE) VOLTAGE

1. Set up the apparatus as shown in Figure 3.



                                                                     OSCILLOSCOPE
                                                                            Sweep Rate
                         AC                  To Ch. 1 of Scope
        Frequency                 1000                                                E
        Counter     ~    Power
                         Supply
                                             and to DVM                              Time / Div.
                         (F.G. 1)                                         L Volts / Div.

                                                                  Ch. 1

                                                                                   Digital
                                                                                   Voltmeter
                                                                           ACV

                                                 Fig. 3


2. Adjust the function generator to 100 Hz at 6 V peak-to-peak.

3 Compute Vrms ( = 0.707 Vo).



                                                - 31 -
4 Record the sweep rate in ms/cm and centimeter per cycle. From the oscilloscope trace,
  estimate the number of centimeters per cycle

   Sweep rate ________________ ms/cm                  convert to _______________ s/cm

   1 cycle spans _________________ cm

   Calculate the period (time for 1 cycle)

   Period ___________ s/cycle = (___________ s/cm) x (___________ cm/cycle)

5. Read the root mean square voltage from digital multimeter and compare to the root mean
   square voltage estimated on the oscilloscope trace. See Fig. 4.

                              Voltage
                              (Volts)




                                                                     
                                 Vo
                     Vrms = 0.707 Vo

                                                                            Vpeak-to-peak
                                                        Time (sec)
                                 -Vo


                                                      Fig. 4

6. Sketch a trace of the 200 Hz AC signal seen on the oscilloscope. Indicate V pp, Vo and Vrms
   on the reticule in the data sheet.

PART III: LISSAJOUS FIGURES

1. Set up apparatus as in Figure 5.

2. Adjust function generator # 2 (F.G. 2) to the same frequency and voltage as function generator
   # 1 (F.G. 1).

3. Observe lissajous figures when F.G. 2 frequency is 2, 3, and 4 times that of F.G. 1

4. Observe the lissajous figures when F.G. 1 frequency is 2, 3, and 4 times that of F.G. 2.

5. Sketch all lissajous figures.




                 To Ch. 1 of Scope                      N
        1000                                                                            1000
    ~              and to DVM           Input                        To Ch. 2 of Scope
                                                                                                    ~
      F. G. 1                            O        R                    and to DVM         F. G. 2
                                        Ch. 1   Ch. 2



                                                      Fig. 5

                                                   - 32 -
DATA SHEET: The Oscilloscope

Data Table 1

Generator
Frequency           Vpeak-to-peak                  Vo                      Calculated Vrms          Vrms From Voltmeter
   (Hz)              (Volts)                     (Volts)                       (Volts)                     (Volts)

   100

   200

  1000

Data Table 2


                                    Frequency From Oscilloscope                                  Frequency From Counter
Generator
                                                                           Frequency         Frequency From     Period From
Frequency
               Sweep Rate                              Period              = 1/ Period           Counter           Counter
   (Hz)
                (msec/cm)           (cm/cycle)       (sec/cycle)              (Hz)                (Hz)           (sec/cycle)

  100

  200

  1000

Trace of AC signal.



          Horizontal: 1 ms / cm

          Vertical: 1 V / div.




Data Table 3: LISSAJOUS FIGURES                   (2 waves with the same amplitude and different frequency whole multiples.)

 Channel 1
(horizontal)
                   60 Hz            100 Hz       100 Hz           100 Hz         200 Hz          300 Hz        400 Hz
Frequency 1
 Channel 2
  (vertical)       60 Hz            200 Hz       300 Hz           400 Hz         100 Hz          100 Hz        100 Hz
Frequency 2


   Sketch
   Trace




                                                           - 33 -
Experiment 12: THE VISIBLE SPECTRUM

PURPOSE:

        The wavelengths of electromagnetic waves in the visible range will be determined with a
diffraction grating.


INTRODUCTION:

        A diffraction grating consists of a number of closely spaced parallel lines ruled on a glass
surface. It is a useful device for separating out the various wavelengths in a spectrum. It has the
same effect as a prism but with greater resolving power.
        According to the theory of interference, the condition for constructive interference is given
by:  = n= d sin where  is the path difference,n is the order number, is the wavelength, d
is the slit separation and  is the diffraction angle.

                                                                  = n
                             
                                                                  = d sin 
                          d 

                                                                  n = d sin 
                                                                 
                                                                             d sin 
                        Fig. 1                         and          =          n

     The diffraction grating spacing d will be determined with a helium-neon laser beam of 633
nm wavelength ().

                                           L
                                                                                         x
White Light                                                                    tan  = L
                                   

                                                                                               L 
              Grating                                                    x
                                                                                = tan-1 x


              d = n/dsin,   n = order number, 1,2…
                                                                Screen

                                  Fig. 2


SUPPLIES & EQUIPMENT:

       Helium-neon laser                       11 X 17 paper                       Laboratory jack
       Grating stand & holder                  Two-meter stick                         One-meter stick
       Large replica grating                   2 ring stands                           Masking tape
       Incandescent light source               2 buret clamps                          Color pencils
       Large cardboard                         Laser safety goggles

                                                       - 34 -
PROCEDURE:

PART A: DETERMINATION OF THE GROOVE SEPARATION d

1. Set up the grating and helium-neon laser. See Figure 3. Set the grating at exactly two meters
   from the chalkboard (L = 2.00). Measure the distance x for the 1 st and 2nd order (n = 1 and 2)
   bright fringes from the central spot. Determine an average value for the groove spacing d
   from your data. The wavelength of the laser light is 633 nm.
                                                               xleft


                                                                            0center



                       He-Ne Laser                                                        xright



                        Lab Jack

                                                   Fig. 3

PART B: DETERMINATION OF THE WAVELENGTH RANGES FOR VISIBLE LIGHT

1. Set up the apparatus as shown in Figure 4, replacing the laser with the incandescent source.

2. Record L. Record xupper and xlower for the upper and lower limit of each color band, as shown in
   Figure 4.

3. Calculate .
                                              th
                                             0 order
                                                                       White




           White-light source
                                                                                xupper (Violet)
                                                                       Violet
                                                                       Blue
                                                                                xlower (Violet) = xupper (Blue)
                                                                       Green
                                                                       Yellow
                                                                       Orange
                                                                       Red

                                                   Fig. 4



Color        upper             lower
Violet       400 nm             424 nm
Blue         424 nm             491 nm
Yellow       491 nm             575 nm
Green        575 nm             585 nm
Orange       585 nm             647 nm
Red          647 nm             700 nm             Reference: Handbook of Chemistry and Physics




                                              - 35 -
DATA SHEET: The Visible Spectrum

Data Table A: Distance from grating to screen = L = 2.000 m


Wavelength   n        | xright|   | xleft|   xaverage       tan                        sin             n
                                                                                                    d
                        (m)         (m)        (m)                                                       sin 

             1
  633 nm
             2

Average value of d = ________________ nm


Data Table B: L __________                         (1)  = d sin


Color                  x             tan                          sin                        % difference
                      (m)                                                             (nm)

Violet           xu                                                             u
                 xl                                                             l
                 xu                                                             u
Blue             xl                                                             l
                 xu                                                             u
Green            xl                                                             l
                 xu                                                             u
Yellow           xl                                                             l
                 xu                                                             u
Orange           xl                                                             l
                 xu                                                             u
Red              xl                                                             l




                                                  - 36 -
Experiment 13: REFLECTION AND REFRACTION
               AT PLANE SURFACES
PURPOSE:

a) To verify the law of reflection.
b) To show by ray tracing, the position and orientation of the virtual image of an object placed in
   front of a plane mirror.
c) To determine the refractive index of glass by ray tracing and application of Snell's law.


INTRODUCTION:

       The law of reflection states that the angle of incidence i of light rays is equal in magnitude
to the angle of reflection r.


                                             i     r



                                          Fig. 1. Reflection

       The law of refraction, Snell's law, states that:    n1 sin 1 = n2 sin 2.




                                          Fig. 2. Refraction


where n1 and n2 are the refractive indices of two different mediums. The refractive index of a
medium is defined as the ratio of the velocity of light in air, c = 3.00 X 10 8 m/s, to its velocity in
that medium. The refractive index of air is 1.000. The refractive index of any medium can be
determined by measuring the angle of incidence, 1, the angle of refraction 2 and applying
Snell's law.


SUPPLIES & EQUIPMENT:

       Cork board           Plane mirror           Long common pins            Wood block
       Plate glass          11 X 17 paper      Colored pencils             Masking tape
       Refraction cube      Ruler & protractor


                                                  - 37 -
PROCEDURE:


PART A: REFLECTION

1. Draw a straight line across the middle of the paper and then draw a triangle with vertices A, B
   and C. Tape the mirror to a block and set it vertically on the line so that the reflecting surface
   (back side) is on the line. The setup is shown in Figure 3 below:




                                                Fig. 3



2. Place a pin at vertex A. From the right side of this triangle, look into the mirror for the image of
   pin A in the mirror. Regard the image in the mirror as A. Place a pin R1 in front of this image,
   A. Along your line of sight *, place another pin R2 in front of R1 so that A and R1 both appear
   to be right behind it. Draw a line joining the points R 2 and R1 and extend this line to the mirror
   surface. Remove pins R1 and R2.

   * Make sure that your eye level and the pins are on the same plane.

3. Repeat the same procedure to the left side of the triangle. With pin A still in place, locate L 1 in
   front of A and L2 in front of L1. Join points L1 and L2 and extend the line to the mirror surface.
   Remove pin A.

4. Place a pin at B. Repeat steps 2 and 3 for points R B1 and RB2, LB1 and LB2. Extend lines
   RB1 RB2 and LB1 LB2 to the surface of the mirror.

5. Place a pin at C, repeat steps 2 and 3 for point C.

6. Remove the mirror and extrapolate the lines until they intersect at A, B and C. Join points
   A, B and C to reconstruct the mirror image (virtual). Fold the paper along the mirror line and
   hold it against the light to see if the object ( ABC) and the image ( ABC) can be
   superimposed on each other.



                                                - 38 -
7. For the vertex A only, draw a line from vertex A to the point where the line R 1R2 meets the
   mirror. Construct a normal to the mirror at this point. Measure the angles of incidence and
   reflection with a protractor. See Figure 3.

PART A: REFRACTION

1. Using another sheet of paper, draw two straight lines perpendicular to each other. Measure
   and draw the three angles 1, 2, and 3. Make your angles 15o, 30o and 45o respectively
   from the normal. The setup is shown in Figure 4. Place the glass cube along the horizontal
   line and trace the outline of the glass cube.




                                            Fig. 4

2. Place pins A and R as shown in Figure 4. Use a locater pin L to line up A and R that are on
   the 15o line. Pins L and R should be as close to the glass surface as possible. Repeat the
   procedure for the 30o and 45o angles.

3. Measure the angle of refraction for each incident angle. Use Snell’s law to compute the index
   of refraction of the glass for each incident and refracted ray. Average three suitable values
   and report an average index of refraction for the glass. Look up the literature value of the
   index of refraction for plate glass. Compare your result to this value.

DATA SHEET: Reflection and Refraction at Plane Surfaces

Your drawings are part of your data.


Incident angle          1 = 15o          2 = 30o           3 = 45o


Angle of Refraction

Refractive Index of
glass (n)


n(average)


                                             - 39 -
Experiment 14: THE THIN LENS

PURPOSE:

       The purpose of this laboratory exercise is to investigate the way in which the image
distance, object distance and focal length for a thin lens are related.


INTRODUCTION:

       The lens equation which relates the object distance, d o, image distance, di, and the focal
length, f, for a glass lens is:



                                                                  f
               1   1 1
                              Eq. 1
              do   di f
                                                             do               di



       In this experiment, we will use an optical bench to align a lighted object, a lens and a
screen. Light rays from the object,       , which pass through the lens will form real images that can
be focused on the screen. Observations will be made as to the nature of the image, that is,
whether it is real or virtual, erect or inverted, and magnified or reduced. Image location can be
estimated with the use of ray diagrams.

       Examples of ray diagrams for convex and concave lenses.




                                                         Object
    Object         F              F     Real
                                        image                         F   Virtual        F
                                                                          Image




                  Convex lens                                             Concave lens


SUPPLIES & EQUIPMENT:

       Optical bench & accessories        20 cm double concave lens
       Ruler                              20 cm double convex lens



                                                - 40 -
PROCEDURE:

1. Determine the focal length of the convex lens that you are using by mounting the lens in a
   stand at a distance from a window. Adjust the distance from the lens to a paper screen until
   the image of an object outside the window is in sharp focus. Deduce the focal length of your
   lens by using equation (1), with do = ∞.

2. Mount the lens at the midpoint of the optical bench and mount the screen and object lamp on
   opposite sides of the lens.

3. Place the object at a position that is somewhat greater than twice the focal length of the lens
   (do > 2f). Move the screen until you get a sharp focus. Describe the characteristics of the
   image. Record the image distance and the object distance. Calculate the image distance
   using Eq. 1.

4. Repeat step 3 for the object at exactly twice the focal length (d o = 2f).

5. Repeat step 3 for the object at somewhere between twice the focal length and the focal length
   (2f > do > f).

6. Repeat step 3 for the object at exactly the focal length (d o = f).

7. Place the object at a distance that is within the focal length. Look through the lens and
   describe the nature of the image (do < f).

8. Replace the biconvex lens with one that is biconcave. Look through the lens at the object and
   describe what you observe.

9. Calculate the image distance di for images seen through the biconcave lens using the lens
   equation.

10. Calculate the image height hi using the magnification equation.

       | M | = | - di / do| = hi / ho

       hi = ho | di / do|

11. On the graph paper, draw ray diagrams to scale. Indicate the scale used.

    1.0 cm = ________ cm




                                                 - 41 -
DATA SHEET: Thin Lens               Focal length from step 1: _______________ m
A. Data for step 3: (do > 2f)                         Characteristics of Images
      do = ______________                             Real / Virtual
       di = ______________ (Calculated)                Upright / Inverted
       di = ______________ (Measured)                  Enlarged / Diminished / No Image


B. Data for step 4: (do = 2f)
      do = ______________                              Real / Virtual
      di = ______________ (Calculated)                 Upright / Inverted
      di = ______________ (Measured)                   Enlarged / Diminished / No Image


C. Data for step 5: (2f > do > f)
       do = ______________                             Real / Virtual
       di = ______________ (Calculated)                Upright / Inverted
       di = ______________ (Measured)                  Enlarged / Diminished / No Image


D. Data for step 6: (do = f)
      do = ______________                              Real / Virtual
      di = ______________ (Calculated)                 Upright / Inverted
                                                       Enlarged / Diminished / No Image

E. Data for step 7: (do < f)
      do = ______________                              Real / Virtual
      di = ______________ (Calculated)                 Upright / Inverted
      di = ______________ (Measured)                   Enlarged / Diminished / No Image


F. Data for step 8: f = -                      cm

(do > f)             do = ______________                        Real / Virtual
                     di = ______________ (Calculated)           Upright / Inverted
                     hi = ______________ (Calculated)           Enlarged / Diminished / No Image


(do = f)             do = ______________                        Real / Virtual
                     di = ______________ (Calculated)           Upright / Inverted
                     hi = ______________ (Calculated)           Enlarged / Diminished / No Image

(do < f)             do = ______________                        Real / Virtual
                     di = ______________ (Calculated)           Upright / Inverted
                     hi = ______________ (Calculated)           Enlarged / Diminished / No Image

                                              - 42 -
RAY DIAGRAMS FOR CONVEX LENSES:



      a.      . .                                          b.   . .
                F                                                  F




      c.      . .                                          d.   ..     No Image

                   F                                              F




                            Virtual Image



                             e.              .             .
                                                           F




RAY DIAGRAMS FOR CONCAVE LENSES:




 a.         . .F                                      b.        . .
                                                                   F




 c.        . F.                                       d.        . .F


                       e.                   ..
                                             F


                                             - 43 -
Experiment 15: ATOMIC SPECTRA

PURPOSE:

       The purpose of this experiment is to measure the wavelengths of light emitted by atoms of
different elements.


INTRODUCTION:

        The electrons of gases can be raised to excited states if the atoms of the gas absorb
specific quanta of energy. The electrons are said to have been raised from their ground state to
higher energy levels. When these electrons fall back to the ground state or to another lower level,
light is emitted. These photons have unique wavelengths corresponding to the difference in
energy between the two states of the electron as it falls.
        In this experiment, high voltage supplies the energy to the atoms in the gas discharge tube.
The electrons are excited and fall to a lower state almost immediately. The mixture of light
produced can be separated using a diffraction grating and then the wavelength can be calculated
from the equation = d sin.


SUPPLIES & EQUIPMENT:

       Spectrum tube power supply         Ar, He, H Spectrum tubes           2 ringstands
       2 One-meter sticks                 2 Buret clamps                     Grating
       Grating holder & stand             Small reading lamp


PROCEDURE:

1. Set up the apparatus as shown in Figure 2.

2. Adjust your eyes in a position such that you can locate the first order spectral lines.

3. Determine the x and L for each spectral line for argon, helium and hydrogen

                                        L 
4. Determine tan  = x and  = tan-1 x .
                        L

5. Determine the wavelength,  of the spectral lines. The grating has 600 grooves per millimeter.
   The grating constant, d, is the distance between the grooves on the grating. For our gratings,
   d = 6001000 in units of nanometers.

6. Compare these wavelengths with the known spectral line values given.




                                                - 44 -
                                                              e
                   +V                                                                    1

                                                                                            Photon
            Gas                                                                             Emission
            Discharge                                                              e                         2
            Tube



                   V                                                  e                           3



                                                          Fig. 1


                                                                                        1st Order        1 = d sin 1
                                                                                        Spectral         2 = d sin 2
                                                                                        Lines            3 = d sin 3




                                  1,  2,  3




                                    Light Rays

         Gas Discharge   Meter              Virtual Image of        Grating             Line Spectrum of this gas
         Tube            Stick              Spectral Line                               Displayed on screen or
                                                                                        eyes




                                                 x
                                                                              

                                                      L = 1 meter
                                                                                         Eye



                                            tan  = x/L   tan1(x/L)

                                                          Fig. 2

Selected spectral line wavelengths (in nm, See Handbook for complete description)

Helium                    Argon                                   Hydrogen                   
Red          668 nm        Red                    697 nm            Red                    656 nm
Yellow       588 nm        Orange                 642 nm            Turquoise              486 nm
Green        502 nm        Green                  523 nm            Purple                 434 nm
Blue         447 nm        Blue-Violet            452 nm            Violet                 410 nm
Violet       403 nm

                                                          - 45 -
DATA SHEET: Atomic Spectra

Data Table 1: Argon

Line Color               Red         Orange         Green        Blue

x (right)       (m)

x (left)        (m)

x (average)     (m)



               (nm)

 (known)       (nm)

% difference

Data Table 2: Helium

Line Color                     Red       Yellow         Green           Blue

x (right)       (m)

x (left)        (m)

x (average)     (m)



               (nm)

 (known)       (nm)

% difference

Data Table 3: Hydrogen

Line Color                     Red     Blue-Green       Purple          Violet

x (right)       (m)

x (left)        (m)

x (average)     (m)



               (nm)

 (known)       (nm)

% difference


                                         - 46 -
Experiment 16: RADIOACTIVITY

PURPOSE:

       To learn about the operation and the use of a geiger counter in the detection of radiation.


INTRODUCTION:                  The Geiger Counter

                                                        Ion – Electron Pair
                                                +
                Ionizing                    -
                Radiation                                               Output to Counter


                                                    -      +

                            Optimum voltage is about 50 V the knee.
                CPM


                                     Knee                                     Avalanch Region


                                                               Plateau Region


                                                                                                 Voltage



SUPPLIES & EQUIPMENT:                           Geiger counter                                  Geiger tube


DATA SHEET: Radioactivity

Radiation measurements at optimum voltage ______________ V


                                         Counts per 30 seconds                          Counts per minute

Front of Room

Near Door

Near Window

Back of Room

Near Door




                                                            - 47 -
DEMONSTRATION LABORATORY ASSIGNMENT

                INTERFERENCE
                     DIFFRACTION
                          POLARIZATION
                               TOTAL INTERNAL REFLECTION
                                    COLOR PERCEPTION
                                         PIN-HOLE CAMERA

Part I

     There are nine lab stations that will serve to demonstrate some interesting optics
phenomena.

         1. Soap bubble.

         2. Hologram - car - interference

         3. Optical flats - air gap - interference

         4. Color Box - color addition and subtraction

         5. Michelson's interferometer - interference pattern

         6. Single slit diffraction - positive and negative slit

         7. Polarized light - water surface - Brewster's angle - polarization

         8. Total internal reflection--rainbow and fiber optics

         9. Pin-hole camera


      View the demonstration at each lab station, and write a paragraph describing your
observations and explaining the principles behind each demonstration.

Part II (Extra credit 10 pts.)

         Construct a diffraction (pin-hole) camera.
Apparatus Notes:

1. Soap bubble: 1 part glycerin, 4 parts clear detergent, 10 parts water. Specify position of parts
   of setup with masking tape on table.

2. Hologram: Diffuse sodium light with ground glass screen to prevent glare. Use black shield
   and black paper underneath.

3: Optical flats: Diffuse sodium light with ground glass screen to prevent glare. View from one-
   half to one meter away.

4. Color Box: Put out overhead projector with cardboard cover pieces also.

5. Michelson's interferometer: Put screen at least 2 m away.

6. Single slit diffraction - positive and negative slit multiple slits. Project on blackboard across
   room. Use 2 pieces of paper 1' x 2.5' for screens.

7. Polarized light: Use circular adjustable polaroid holder. Use blue battery charger set at 6V and
   12 V Pasco lamp.

8. Total internal reflection: Use large (8") crystallizing dish from chemistry. Place screen about a
   meter away. Use slit opening over lamp. Use a red battery charger set at 12V and 12 V
   Pasco lamp. Shield apparatus from stray light. Use lab jack for laser.

9: Pin-hole camera
STATION #1
THIN FILM

LIGHT
INTERFERENCE




                 PATH DIFFERENCE
                 IMPORTANT
       Soap
      Solution
                 BRIGHT FRINGE
                 WHEN IN STEP
STATION #2


HOLOGRAPHY                   INTERFERENCE




                  Hologram
                   of Car

                              Sodi um

       Lab Jack                Lamp
STATION #3


OPTICAL FLATS                                           AIR GAPS
                                                 INTERFERENCE




            Vi ew From Distance



                           Microscope Sl id e - Not Very Fl at



                                                                   Sodi um
                                                                    Lamp
                           Op ti cal Flats -- Very Fl at
STATION #4
COLOR BOX           COLOR ADDITION:    LIGHT SOURCES

Color addition by
the mixing of
colored lights.
When three
projectors shine
red, blue, and                                          COLOR ME
green light on a                                           RED

white screen, the
overlapping parts
                                                  COLOR ME    COLOR ME
produce different                                 MAGENTA      YELLOW

colors. The                                              PLEASE
                                                          DON' T
                                                        COLOR ME
addition of the
three primary                                            COLOR ME
                                                          CYAN
                                             COLOR ME
colors produces                                BLUE
                                                                    COLOR ME
                                                                     GREEN
white light.

COLOR SUBTRACTION:           FILTERS
STATION #5
MICHELSON'S
INTERFEROMETER
                                  Laser Li ght Source




                                   Half-silvered mirror

                                                          Movable Mirror


 Screen 2 meters Away
                                  Compensator
INTERFERENCE
PATTERN


                        Fixed Mirror
STATION #6
DIFFRACTION

        MULTIPLE SLIT (4 Slits)


   0.5 mW He-Ne Laser


                                            Pape r Screen
                                            on Bl ackboard




        SINGLE SLIT               A. SLIT     + SLIT
  0.5 mW He-Ne Laser




                                  B. HAIR - SLIT
STATION #7
POLARIZATION :

      UNPOLARIZED                         POLARIZED               WATCH
      WHITE LIGHT                             LIGHT                  THIS

                                                         




                                  POLAROID            POLAROID        AS YOU
                                    #1 =                #2 =          ROTATE THE
                                  POLARIZER           ANALYZER        ANALYZER

POLARIZATION BY REFLECTION:

                             qB
                        Ai r
                        Gl ass
STATION #8
TOTAL INTERNAL REFLECTION:      RAINBOW AND FIBER OPTICS



                                               WATER
                                               DROPS
                             SUNLIGHT

                                        40 O




                   VIOLET                  42 O


                RED
              VIOLET
                       RED
      Translucent white
       paper 1 m away
      wi ll show rainb ow
      on opposite si de




White l i ght source



                            Large Crysta ll izi ng di sh with
                            very di lute u nfl avored gel ati n
                            1:100 ?
STATION #9
PIN-HOLE CAMERA:




                   Source

                            Inverted i mage on
                            froste d gl ass screen

				
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