# lab - power transmission ib2

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```							Date Performed: ____________            Date Due: ______________               Date Handed In: ___________            Raw Score:      / 60
GOOD COPY If this copy is neat, you do not need to rewrite it.         If not, rewrite it neatly on loose leaf or a
clean copy of this sheet found on the class website. Neatness is part of the grade for the lab.               Final Grade:    / 25

IB 12
Name: ________________________________                                                            Row : ______
Partners:

ACTIVITY: Power Transmission
To get1. basic overview of how electrical energy makes it from the power generating station to your home,
a
read the article on “How Power Grids Work” at http://science.howstuffworks.com/power.htm and answer
the following questions.
[7]
1. Identify each of the main parts of the power grid pictured at right.

A:

B:

C:

D:

E:

F:

G:
2. What are some ways to cause a generator in a power plant to spin?                                                          [2]

[1]
3. What do commercial electrical generators of any size generate?

[2]
4. Single phase AC service consists of power that varies like a sine wave which has:

a) a peak voltage of:                                 b) an effective (rms) voltage of:

[1]
5. What is the purpose of a transmission substation?
6. What are typical voltages for long distance transmission?                                         [1]

7. What is the purpose of step-down transformer in a power substation?                              [1]

[1]
8. What is the purpose of a transformer drum seen on a power pole?

Next, you are going to investigate the operations of two of the main components of the power grid –
the generator and the transformer.
to learn how an AC generator operates and answer the following questions.
[1]
9. What is the purpose of an AC generator?

10. An AC generator works on the principle of electromagnetic induction. Explain what this             [1]
principle means.

11. Briefly describe how an AC generator works. (Use your notes and watch the animation.)               [2]
f = 6.0 rotations/minute

12. Be sure the frequency of the generator is set to 6.0 rotations per minute. Watch the wire loop
rotating in the magnetic field and follow how it corresponds to the induced emf (U) by following
the needle of the voltmeter and the moving blue dot on the graph.

a) Label on the graph above two spots where the wire loop is parallel to the magnetic field lines.
Label these spots A.                                                                            [2]

b) Do these locations correspond to                                                                  [3]
a. Maximum or minimum flux through the loop?

b. Maximum or minimum emf?

c. Maximum or minimum current in the circuit?

c) Label on the graph above two spots where the wire loop is perpendicular to the magnetic field
lines. Label these spots B.                                                                   [2]

d) Do these locations correspond to                                                                  [3]
a. Maximum or minimum flux through the loop?

b. Maximum or minimum emf?

c. Maximum or minimum current in the circuit?

f = 12.0 rotations/minute

13. Double the frequency to 12.0 rotations per minute.
a) State what happens to the period of rotation and the maximum emf produced when the              [2]
frequency is doubled.

b) Sketch on the diagram above how this changes the output emf.                                      [2]
Now go to http://ecmweb.com/ops/electric_basics_transformers_2/ to learn how a transformer
works and answer the following questions.

14. What is the purpose of a transformer?                                                        [1]

[3]
15. Sketch and label the three main parts of a simple transformer.

16. Describe how a transformer works, using the concept of magnetic flux.                        [2]

[1]
17. What is the purpose of the iron core?

Go to http://micro.magnet.fsu.edu/electromag/java/transformer/index.html and play with
the animation to answer the following questions.
18. As you increase the number of windings in the primary coil, what happens to the output voltage?
[1]

19. As you increase the number of windings in the secondary coil, what happens to the output voltage?
[1]

20. In a step-up transformer:                       21. In a step-down transformer:               [2]
[2]
a) which coil has more windings?                     a) which coil has more windings?

b) which coil has a higher voltage?                  b) which coil has a higher voltage?
Next, you are going to learn about some of the possible risks associated with power
transmission. First, go to
http://www.hpa.org.uk/webw/HPAweb&HPAwebStandard/HPAweb_C/1197636999087?p=1
158934607683 to read through the slide show about electric and magnetic fields and their
effects on the human body.
[2]
22. How do electric and magnetic fields occur in the home?

23. Under a high-voltage power line, what is the strength of a typical                     [2]

a) electric field?                           b) magnetic field?
[1]
24. What can electric and magnetic fields induce in the human body?

Lastly, go to
http://www.hpa.org.uk/webw/HPAweb&HPAwebStandard/HPAweb_C/1197637106633?p=11

25. What is non-ionising radiation? What parts of the EM spectrum does it include?         [2]

26. What does ELF stand for? Does this type of radiation have enough energy to damage      [2]
DNA in the nucleus?

27. What are the main contributions to people’s exposure to ELF radiation?                 [2]

28. What are the established health effects associated with exposure to ELF radiation?     [2]

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