# PHY 101 – Introduction to Physics_3_ by malj

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```									       PHY 112 – General Physics II
n   MWF 8-9:50 am or 11-12:50 pm
n   Instructor: Heidi Van Tassell
n   Office: PS 211
n   Office Hours:
Monday: 10:00-10:50 am in PS108
Tuesday: 9:30-10:20 am in PS211
Wednesday: 10:00-10:50 am in PS108
Thursday: 9:30-10:20 am in PS211
Friday: 10:00-10:50 am in PS108
n   Email: vantassell@mesacc.edu
n   Webpage: www.mesacc.edu/~vantassell

MCC PHY112 - Van Tassell - 2/3/2012   1
Announcements
qExam   3
n Friday 20 April 2012

n Chapters 21, 22

ASU PHY112 - Van Tassell - 1/28/2011   2
n   Lab 11.3: Refraction

MCC PHY112 - Van Tassell - 3/4/2011   3
Refraction
n   When light reaches a boundary between two media it
may either reflect off the boundary and return through
the media it came, or it will pass through the new
media.

n   Refraction is the bending of light rays as they pass
from one media to another.

ASU PHY112 - Van Tassell -4/16/2007    4
Refraction
n   Refraction occurs due to the difference in the speed of
light in different media.

n   Atoms in the materials absorb, reemit, and scatter the
light causing delays in the transmission of the light.

n   This slowing of light causes wave fronts to bend at the
boundary as part of the wave front move at different
speeds.

ASU PHY112 - Van Tassell -4/16/2007     5
Refraction
n   The index of refraction measures the extent to which
light is slowed in a medium as compared to vacuum.

n   A table of refractive indices is available on page 808 of

ASU PHY112 - Van Tassell -4/16/2007      6
Refraction
n   Snell’s law describes how much light is bent at a
boundary:

n   As with the law of reflection, angles for refraction are
measured relative to the normal to the boundary.

ASU PHY112 - Van Tassell -4/16/2007    7
Refraction
n   Example: The drawing shows three layers of liquids, and a ray of
light incident on the top layer. What angle does the ray of light
make with the normal in the different materials?

ASU PHY112 - Van Tassell -4/16/2007       8
Refraction

n   Example: The drawing shows a block of diamond. Where does
the light go?

ASU PHY112 - Van Tassell -4/16/2007      9
Refraction
n   This is called total internal reflection, and is the basis
for fiber optics.

n   Fiber optics is used in the telephone industry,
medicine, and a variety of other high tech industries.

ASU PHY112 - Van Tassell -4/16/2007      10
Refraction
n   Some materials have indices of refraction that are not
constant, but vary instead with wavelength or
frequency.

n   In this case red light and blue light would bend by
different amounts when entering the material.

ASU PHY112 - Van Tassell -4/16/2007   11
Refraction
n   The result of sending white light incident upon such a
material would be to have dispersion.

n   Dispersion is the spreading of light into its color
components by a frequency dependent refraction.

n   Dispersion is the principle behind prisms.

ASU PHY112 - Van Tassell -4/16/2007   12
Refraction
n   Dispersion is the principle behind prisms.

ASU PHY112 - Van Tassell -4/16/2007   13
Refraction
n   Dispersion by rain droplets causes rainbows to appear
in the sky.

n   Each rainbow you see is unique for you as a different
person, standing at a different location will have light at
different incident angles, creating a whole different and
unique rainbow.

ASU PHY112 - Van Tassell -4/16/2007   14
Mirrors
n Last time we discussed the law of reflection and
through ray tracing discovered how spherical
mirrors form images.
n Today we offer an analytical approach to finding
images produced by spherical mirrors.

ASU PHY112 - Van Tassell -4/16/2007   15
Mirrors
n   First we define some variables:
¨ f=focal length – distance from mirror to where rays
parallel to the optical axis meet.
¨ do=object distance – distance from mirror to object
¨ di=image distance – distance from mirror to image
¨ m=magnification – the ratio of the height of the
image ot the height of the object.

ASU PHY112 - Van Tassell -4/16/2007    16
Mirrors
n   The mirror equation:

n   The magnification equation:

ASU PHY112 - Van Tassell -4/16/2007   17
Mirrors
n   Sign Conventions:
¨ Focal   lengths:
n + for concave mirrors
n - for convex mirrors

¨ Object   distance
n + if the object is in front of the mirror (real object)
n - if the object is behind the mirror (virtual object)

ASU PHY112 - Van Tassell -4/16/2007     18
Mirrors
n   Sign Conventions:
¨ Image   distance:
n + if the image is in front of the mirror (real image)
n - if the image is behind the mirror (virtual image)

¨ Magnification:
n + for an image that is upright with respect to the object.
n - for an image that is upside down with respect to the
object.

ASU PHY112 - Van Tassell -4/16/2007          19
Mirrors
n   Example: A 2.0 cm high object is placed 8.3 cm in front of a
concave mirror whose radius of curvature is 12.0 cm. Find the
location and description of the image.

ASU PHY112 - Van Tassell -4/16/2007         20
Mirrors
n   Example: A 2.0 cm high object is placed 8.3 cm in front of a
concave mirror whose radius of curvature is 12.0 cm. Find the
location and description of the image.

ASU PHY112 - Van Tassell -4/16/2007         21
Mirrors
n   Example: A 2.0 cm high object is placed 8.3 cm in front of a
concave mirror whose radius of curvature is 12.0 cm. Find the
location and description of the image.

n   Description of the image:
¨ The image is real because di>0
¨ The image is inverted because m<0
¨ The image is enlarged because |m|>1

ASU PHY112 - Van Tassell -4/16/2007         22
Mirrors
n   Description of images:
¨ The image is real if di>0
¨ The image is virtual if di<0

¨ The image is upright if m>0
¨ The image is inverted if m<0

¨ The image is reduced if |m|<1
¨ The image is enlarged if |m|>1
¨ The image is the same size as the object if |m|=1

ASU PHY112 - Van Tassell -4/16/2007   23
Mirrors
n   Example: A convex mirror is used to reflect light from an object
placed 60 cm in front of the mirror. The focal length of the mirror
is f=-46 cm. Find the location and description of the image.

ASU PHY112 - Van Tassell -4/16/2007        24
Mirrors
n   Example: A convex mirror is used to reflect light from an object
placed 60 cm in front of the mirror. The focal length of the mirror
is f=-46 cm. Find the location and description of the image.

ASU PHY112 - Van Tassell -4/16/2007        25
Mirrors
n   Example: A convex mirror is used to reflect light from an object
placed 60 cm in front of the mirror. The focal length of the mirror
is f=-46 cm. Find the location and description of the image.

n   Description of the image:
¨ The image is virtual because di<0
¨ The image is upright because m>0
¨ The image is reduced because |m|<1

ASU PHY112 - Van Tassell -4/16/2007        26
Mirrors
n   Convex and planar mirrors always produce virtual
images of real objects.

n   Concave mirrors may produce real or virtual images of
real objects.

ASU PHY112 - Van Tassell -4/16/2007   27
n   A mirror produces an image that is located 34.0 cm
behind the mirror when the object is located 7.5 cm in
front of the mirror. What is the focal length of the
mirror, and is the mirror concave or convex?

ASU PHY112 - Van Tassell -4/16/2007    28
Mirrors
n   Example: A mirror produces an image that is located 34.0 cm
behind the mirror when the object is located 7.5 cm in front of
the mirror. What is the focal length of the mirror, and is the
mirror concave or convex?

ASU PHY112 - Van Tassell -4/16/2007          29
n   Lab 12.1 - Lenses

MCC PHY112 - Van Tassell - 3/4/2011   30

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