Induction (DP IB Physics: HL): Exam Questions

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.

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

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?

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?

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?

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

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

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

An ac generator produces a root mean squared emf ε at frequency f. The rotational speed of the coil in the generator is increased by a factor of three. Which of the following correctly identifies the new values of frequency and output emf_rms?

The graph shows the variation with time t of the output voltage V of an ac generator.

Which graph, with identical scales on the axes, shows the output when the speed of rotation is doubled?

An oscillating magnetic field, B, is applied perpendicular to the plane of a small flat coil of copper wire. The equation for the changing flux density is given by:

where B₀ is the amplitude and ω is the angular frequency of the oscillating magnetic field.

If the period of the oscillating magnetic field is T, at what time t, is the magnitude of the induced e.m.f in the coil a maximum?

The south pole of a bar magnet is pushed into one end of a coil of wire, which is connected to a sensitive galvanometer as shown: 

A galvanometer measures the amount of current through a moving coil, shown by a deflecting needle. A maximum deflection of the galvanometer needle of 7 units to the right is observed. 

Next, the north pole of the magnet is pushed into the other end of the coil at twice the speed.

What would be the maximum deflection of the galvanometer needle?

A coil is rotated in a uniform magnetic field. An alternating emf is induced in the coil.

What is a possible phase relationship between the magnetic flux through the coil and the induced emf in the coil when the variations of both coils are plotted with time?

Two circular coils, J and K, share a common axis and are parallel to each other. A constant direct current passes through coil J.

Coil K is moved towards coil J and then moved back to its original position. 

As coil K moves, what is the direction of the current induced in coil K relative to the current in coil J?

A bar magnet moves steadily from right to left through a very long solenoid.

A galvanometer is connected across the solenoid. A galvanometer measures the amount of current (and voltage) through a moving coil, shown by a deflecting needle.

Which graph shows the deflection of the galvanometer, θ with time, t?

A copper ring is suspended by a long, light rod pivoted at X so that it may swing as a pendulum, as shown in the diagram below:

An electromagnet is set up so that the ring can pass over it as it swings. The ring is then set into oscillation at time t = 0, with switch K open. It completes two full oscillations, at which point the switch K is closed at time t = t₀

Which graph correctly shows the variation of the displacement x with time t?   

The Olympic torch can be modelled as a 1.0 m long conducting rod. People jogging can be said to average between 6.4 – 9.7 km h⁻¹.

The torch is carried along streets in towns around the world. On which part of the route shown is the induced e.m.f. at a maximum, and what is the approximate motional e.m.f. induced in the metal of the torch when carried along this street by a brisk jogger?

Assume that the Earth’s field has magnetic flux density, B = 50 µT.

A coil, P, is connected to an alternating supply of potential difference. Another coil, Q, is placed nearby and connected to an oscilloscope. 

A thick iron loop is now introduced, such that it passes through the centre of coil P and the centre of coil Q. 

Which of the following shows the effect on the oscilloscope trace of introducing this new component?