10 minutes maximum! (can you do it in 5?)
1. Magnetic Flux Φ through a surface is defined as Φ = BA cos θ.
A is the area of the surface. Which of these descriptions correctly identifies B and θ? 


B 
θ 
A 
Magnetic field strength 
angle between surface and magnetic field lines 
B 
Magnetic flux linkage 
angle between surface and magnetic field lines 
C 
Magnetic field strength 
angle between line perpendicular to surface and magnetic field lines 
D 
Magnetic flux linkage 
angle between line perpendicular to surface and magnetic field lines 


2. The units for B and Φ are:

B 
Φ 
A 
weber 
tesla m^{2} 
B 
tesla m^{2} 
tesla 
C 
tesla 
weber 
D 
tesla m^{2} 
weber 


3. A coil is placed perpendicular to a uniform magnetic field.
Which of the methods listed on the right will induce an emf in the coil?
 A. I only
 B. I and II
 C. II and III
 D. I, II and III

I. Rotate the coil.
II. Produce a varying magnetic field strength.
III. Move the coil backwards and forwards parallel to the field lines.


4+5. The diagrams here show a wire XY being moved through two magnetic fields, P and Q.
The wire is connected to an external circuit (not shown) so a current can flow.
4. Which of the answers below show the direction of the induced current in the wire in diagrams P and Q? 


field P 
field Q 
A 
X to Y 
X to Y 
B 
X to Y 
Y to X 
C 
Y to X 
X to Y 
D 
Y to X 
Y to X 


5. In the diagrams above, The magnitude of the induced emf can be varied in several ways. Which of these changes will have no effect on the magnitude of the induced emf?
 A. Increasing the length of the wire XY without increasing the dimensions of the magnetic field.
 B. Increasing the length and width of the magnetic field, without changing the field strength.
 C. Increasing the velocity of the wire through the field.
 D. Increasing the field strength without increasing the area of the field.


6. The north pole of a magnet is moved downwards at 1 ms^{1} past a stationary wire XY as shown in the diagram:
The magnetic field is uniform and perpendicular to the wire, of magnetic flux density 0.1 mT. The wire is completely within the field, and is 2 cm long. 

The induced emf magnitude and direction (high to low potential) in the wire is:
 A. 0.2 mV from X to Y
 B. 0.2 mV from Y to X
 C. 2 µV from X to Y
 D. 2 µV from Y to X


7+8. "The direction of the current induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes the initial changing magnetic field." * 
*(Wikipedia) 
7. This law is:
 A. Lenz's Law
 B. Malus' Law
 C. Faraday's Law
 D. Tesla's Law


8. A magnet is dropped towards a coil as shown here:


Due to the law stated above, the current flowing in the front section of the coil PQ will be:
 A. From P to Q so the magnet is repelled from the coil.
 B. From Q to P so the magnet is repelled from the coil.
 C. From P to Q so the magnet is attracted towards the coil.
 D. From Q to P so the magnet is attracted towards the coil.


9 & 10. A rectangular coil of 1000 turns and area 0.01 m^{2} is within a magnetic field of strength 0.1 T.
It is rotating with a frequency of 0.25 Hz. 

9. If the coil is initially perpendicular to the field, what is the minimum elapsed time before the flux linkage is zero?
 A. 4 seconds
 B. 2 seconds
 C. 1 second
 D. 0.5 seconds


10. What is the average emf induced in the coil during this time?
 A. 1 volt
 B. 0.1 volts
 C. 0.01 volts
 D. 0.001 volts


