A coil rotates in a uniform magnetic field. The graph shows the variation with time t of the magnetic flux φ through a coil.
Determine the times when the magnitude of the induced emf measured across the ends of the coil is at a minimum.
t1 only
t1 and t4
t2 and t3
t2 and t4
A length of conducting wire XY is moved downwards through the poles of a horseshoe magnet.
This will change the ends of the wire so that compared to end Y of the wire, end X will have
More electrons
Fewer electrons
More protons
Fewer protons
A square coil of conducting wire with sides of length W is moved at constant speed v left to right, through a uniform magnetic field which is directed into the page and has width W.
From the point where the coil enters the field until the point where it leaves it, which description best fits the direction of the current induced in the coil?
Anti-clockwise
Clockwise
Anti-clockwise then clockwise
Clockwise then anti-clockwise
Three loops of wire are arranged so that the current flowing in loop X in a clockwise direction induces a current in both in loops Y and Z. The three loops are all on the same plane.
What is the direction of the induced currents in loop Y and loop Z?
| Loop Y | Loop Z | |
| A. | clockwise | clockwise |
| B. | clockwise | anti-clockwise |
| C. | anti-clockwise | anti-clockwise |
| D. | anti-clockwise | clockwise |
A pendulum made from a flat disk of copper is suspended in a region of uniform magnetic field by an insulating rod connected to a horizontal support. The disk is pulled to one side of the field and then released.
The uniform magnetic field is directed into the plane of the paper.
Which of the following is true for both the direction of the induced current in the disk and the change in amplitude of the oscillations of the pendulum with time?
| Direction of induced current | Change in amplitude | |
| A. | changes | decreases |
| B. | changes | stays constant |
| C. | stays constant | decreases |
| D. | stays constant | stays constant |
A flat coil with N turns has a diameter d. The coil has a flux density of B in a direction of 90° to the plane of the coil.
A second coil has 3N turns and diameter 2d.
Select the correct ratio of 
The graph shows the variation with angle θ of the magnetic flux φ through a coil that is rotating in a uniform magnetic field. θ is measured between the coil and the plane of the magnetic field lines.
Select the graph which correctly shows the variation in emf, ε with angle θ for the same coil.
A coil of conducting wire having N turns is wrapped around a cardboard cylinder. The ends of the coil are connected using a straight piece of conducting wire. The coil is moved towards a permanent bar magnet fixed in position. The coil moves at velocity v.
The induced current in the straight section of wire is
Alternating
Zero
From X to Y
From Y to X
The solid line on the graph shows the variation with time of a magnetic flux passing through a loop of wire. Both the magnetic field strength and the area of the loop are increased but no other changes are made.
The new graph of magnetic flux and time can be represented by the dashed lines labelled
I only
I and II
III only
IV only
Two coils are arranged so that one fits inside the other with the axes parallel. The larger coil has 200 turns and cross-sectional area of 30 cm2. A changing current in the small coil causes the magnetic field to increase at a rate of 0.5 T s–1.
The induced emf in the large coil will be
300 n V
300 µ V
300 m V
300 V
