[Maximum number: 4]

A6. This question is about electromagnetic induction.
(a) State Lenz's law.
(b) Two identical aluminium balls are dropped simultaneously from the same height. Ball P falls through a region with no magnetic field. Ball Q falls through a region of uniform horizontal magnetic flux density B.

Explain why ball Q takes longer than ball P to reach the ground.
This section consists of four questions: B1, B2, B3 and B4.

[Maximum number: 2]

There is a proposal to power a space satellite X as it orbits the Earth. In this model, X is connected by an electronically-conducting cable to another smaller satellite Y .

not to scale

(a)

The magnetic field strength of the Earth is $31 \mu \mathrm{~T}$ at the orbital radius of the satellites. The cable is 15 km in length. Calculate the emf induced in the cable.

[ 2 ]

[Maximum number: 2]

A lighting system consists of two long metal rods with a potential difference maintained between them. Identical lamps can be connected between the rods as required.

The following data are available for the lamps when at their working temperature.

(a)

A step-down transformer is used to transfer energy to the two rods. The primary coil of this transformer is connected to an alternating mains supply that has an emf of root mean square (rms) magnitude 240 V . The transformer is 95 % efficient.

[ 2 ]

(i)

Outline how eddy currents reduce transformer efficiency.

[ 2 ]

[Maximum number: 1]

A magnet oscillates above a solenoid as shown.

The magnet is displaced vertically and released from its highest position at time t=0. Which graph shows the variation with time t of the current I in the resistor?

[Maximum number: 1]

A flat coil with N turns has a cross-sectional area A. The coil has a flux density of B in a direction of $90^{\circ}$ to the plane of the coil.

What is the magnetic flux linkage?

B A

N B

N B A

[Maximum number: 1]

An aircraft with a wing span of 50 m flies horizontally at a speed of $200 \mathrm{~ms}^{-1}$ . The vertical component of the Earth's magnetic field at the plane's position is $10 \mu \mathrm{~T}$ .

What electromotive force (emf) is induced between points A and B on the aircraft?

$0.1 \mathrm{~V}$

$1 \mathrm{~V}$

10 V

100 V

[Maximum number: 1]

Faraday's law of electromagnetic induction states that the electromotive force (emf) induced in a conductor is proportional to

the change of magnetic flux density.

the change of magnetic flux linkage.

the rate of change of magnetic flux density.

the rate of change of magnetic flux linkage.

[Maximum number: 2]

A metal rod is pulled along two horizontal conducting rails X and Y so that it rolls to the right at a constant speed. The two rails are connected by a straight conducting wire of Length $L=0.60 \mathrm{~m}$ . The system is in a region of uniform magnetic field of magnitude $B=1.2 \mathrm{~T}$ directed into the page.

(a)

As a result of the motion, the metal rod experiences a magnetic force of 0.084 N .

[ 2 ]

(i)

Outline how Lenz's law applies to this system.

[ 2 ]

[Maximum number: 1]

The graph shows the variation with time of a magnetic flux passing through a loop of wire.

What is the magnitude of the emf induced in the coil?

The area between the graph and the time axis

The area between the graph and the magnetic flux axis

The gradient of the graph

The inverse of the gradient of the graph

[Maximum number: 4]

This question is about induced electromotive force (emf).

(a)

A loop of copper wire in a region of uniform magnetic field is rotated about a horizontal axis.

The magnitude of the magnetic field strength is B and the area of the loop is A.

[ 4 ]

(i)

State the minimum value and the maximum value of the magnetic flux linking the loop.

Minimum value:
Maximum value:

[ 1 ]

(ii)

Outline with reference to Faraday's law why, if the speed of rotation of the loop is increased, the maximum emf induced in the loop is increased.

[ 3 ]