4.7) Electromagnetism
1) You have a magnet and coil attached to a sensitive galvanometer.
a) What happens as a magnet is moved in and out of the coil?
b) What will happen if the coil and the magnet are moved together? the needle will
A) move more B) move less C) move the same
D) not move
2) A magnet is dropped down a copper tube. What happens to its speed? It accelerates at
A) 9.8 m/s2 B) less than 9.8 m/s2 C) greater than 9.8 m/s2
D) a decreasing rate
3) Draw force diagrams of the magnet at the top, middle and end of the tube.
.
4) Where does the gravitational energy go?
5) How and why is this used for brakes on the Drop Zone?
6) A copper ring surrounds the iron core of an electromagnet.
a) What will happen if the current is turned on?
b) How is this similar to an induction stove?
7) Attach the Lego motors together with a wire.
a) What happens as you turn one? Why?
b) Compare motors to generators.
8) A radio has had the wires leading to the speakers cut. The speaker leads have been attached to a coil of
wire and the radio leads have been attached to another coil of wire.
When the radio is turned on you will hear nothing
A) because the circuit to the speakers has been broken.
B) unless the coils are placed on top of each other.
C) unless the coils are placed on top of each other and are touching.
D) unless the coils are placed close beside each other.
E) unless the coils are placed close beside each other and are touching.
Explain:
9) Go to http://phet.colorado.edu/en/simulation/faraday and select Transformer. There is no current going
through the light bulb. This is because
A) the coils are too far apart
B) the voltage is too low
C) there aren’t enough loops
D) something else
Explain:
For the next four questions use the simulation and the real apparatus.
10) You will decrease the effect if the coil is moved
A) further away
B) so the centers are not aligned
C) both will reduce the effect
D) neither will have an effect
Explain:
11) You can increase the effect by
A) increasing the amplitude of the AC signal
C) increasing both
Explain:
B) increasing the frequency of the AC signal
D) neither will have an effect
12) You can increase the effect by maximizing the number of loops attached to
A) source
B) pick up
C) both
D) neither will have an effect
Explain:
13) You will decrease the effect the most by
A) halving the diameter of the loops
C) they will have equal effects
Explain:
B) doubling the distance
D) they will have no effect
Use just the radio for the next two questions.
14) The sound will be reduced if you place the following materials between the coils
A) iron
B) aluminum
C) aluminum and iron D) paper
E) all of the above
Explain:
15) The sound will be increased if you place the following materials inside the coils
A) iron
B) aluminum
C) aluminum and iron D) paper
E) all of the above
Explain:
16) Maxwell summarized all of electricity and magnetism into four laws. Explain in simple words and
diagrams what each of Maxwell`s Equations means and give an example of how you can demonstrate it.
a)
E = /
b)
B=0
c)
X E = - dB/dt
d)
X B =  I + dE /dt
17) The last term of the last equation was added by Maxwell for reasons of symmetry. He used it to predict
that electric and magnetic fields can form a self-propagating wave whenever a charge is accelerated.
a) Which equation is changed by accelerating a charge and what happens after?
b) The wave has a speed of sqrt (/) where; 4 x 10-7 Tm/A – the magnetic permeability of
free space - and  =1/4k – the electric permittivity of free space. Calculate the
c) You can see this modelled at http://phet.colorado.edu/en/simulation/radio-waves
18) Hot spots are formed in microwave ovens and so a rotating tray is used to heat more evenly. You can
locate the hot spots by placing a layer of chocolate, cheese or marshmallows in the oven. Measure the
separation of the hot spots and use the speed of light to calculate the frequency of the microwaves.
Textbook: 8.5
p. 418 # 1 - 3, p. 419 #1-8, p. 429 # 20