Electromagnetic Induction (CIE A Level Physics)

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A solenoid has a coil C of wire wound tightly about its centre, as shown in Fig. 7.1.

Fig. 7.1

The coil C has 96 turns.
The uniform magnetic flux Φ, in Wb, in the solenoid is given by the expression

Φ = 6.8 × 10^–6 × I

where I is the current, in A, in the solenoid.

Calculate the average electromotive force (e.m.f.) induced in coil C when a current of 3.5 A is reversed in the solenoid in a time of 2.4 ms.

e.m.f. = ................................... V 

The d.c. supply in Fig. 7.1 is now replaced with a sinusoidal alternating supply.

Describe qualitatively the e.m.f. that is now induced in coil C.

A small solenoid of area of cross-section 1.2 × 10⁻³ m² is placed inside a larger solenoid of area of cross-section 7.8 × 10⁻³ m², as shown in FIg. 1.1

Fig. 1.1

The larger solenoid has 800 turns and is attached to a d.c. power supply to create a magnetic field.

The smaller solenoid has 2000 turns.

Compare the magnetic flux in the two solenoids.

Compare the magnetic flux linkage in the two solenoids.

State Lenz's Law of electromagnetic induction.

The terminals of the smaller solenoid are connected together. The smaller solenoid is then removed from the inside of the larger solenoid. 

With reference to magnetic fields, explain why a force is needed to remove the smaller solenoid. 

Define magnetic flux linkage. 

A square coil of wire of side length 10 cm consists of 5 insulated turns. The coil is stationary in a uniform magnetic field. The plane of the coil is perpendicular to the magnetic field, as shown in Fig. 1.1.

The procedure in (b) is repeated, but this time the terminals of the coil are connected together. 

State and explain the effect on the coil of connecting the terminals together during the change of magnetic flux density shown in Fig. 1.2.