# Module

## Module: Motors and Generators

### Question 4

Written Paper Section I Question 4 - 2001 HSC

Type of current produced by each generator illustrated when connected to an external resistance.

### Question 6

Section I Question 6 - 2002 HSC

Role of a transformer at an electrical power station.

### Question 7

Section I Question 7 - 2002 HSC

Magnitude (T) of the external magnetic field on a long current-carrying conductor placed perpendicular to an external magnetic field, given a graph showing how Force (N) varied with Current (A).

### Question 8

Section I Question 8 - 2002 HSC

Direction a single-turn coil of wire coil freely moves, due to the interaction between a uniform external magnetic field and the direction an electric current flows around the coil.

### Question 8

Written Paper Section I Question 8 - 2001 HSC

Condition causing a pendulum which has a coil of copper wire at the non-pivot end and which is swinging above a magnet to come to rest most quickly.

### Question 9

Section I Question 9 - 2002 HSC

Comparison of the time taken for identically oriented bar magnets to hit the floor when they are dropped through tubes of plastic and copper of the same length and diameter.

### Question 10

Section I Question 10 - 2002 HSC

Diagram representing the curve of induced electromagnetic field against position, given the direction of movement of the coil of an AC generator rotating at a constant rate in a magnetic field.

### Question 10

Written Paper Section I Question 10 - 2001 HSC

Graph showing how a current through an electric motor varies with speed, given that the power supply is of constant voltage and that the motor is allowed to run at different speeds by adjusting a brake.

### Question 11

Written Paper Section I Question 11 - 2001 HSC

Calculation of the secondary voltage to a transformer, given that the primary voltage is 110 V and the primary coil has 60 turns and the secondary coil has 2300 turns.

### Question 14

Written Paper Section I Question 14 - 2001 HSC

Forces acting on two straight metal rods of the same length, each pivoted at one end, each rotated with the same angular velocity so that they sweep out horizontal circular paths, and each with a constant current flowing along it.

### Question 21-23

Written Paper Section I Question 21-23 - 2001 HSC

Q21. Explain why no resistance is required when a large d.c. motor is running at high speed, but a substantial resistance is needed when the motor is starting up. Q22. Identify the direction of the force that exists between two parallel wires, each with a current flowing in the same direction along the wires. On a set of axes, sketch a graph that shows how the force between the two wires would vary if the length of the shorter wire were increased. Explain how these results demonstrate the moto-effect. Q23. Discuss the effects of the development of electrical generators on society and the environment. Outline the methods of X-ray diffraction used by the Braggs to determine the structure of crystals.

### Question 22

Section I Question 22 - 2002 HSC

(a) Identify the function of the brush in a generator. (b) Determine which of the generators illustrated is a DC generator and justify your choice. (c) Outline why AC generators are used in large-scale electrical power production.

### Question 23

Section I Question 23 - 2002 HSC

(a) State Lenzâ€™s law. (b) Determine which end of a metal rod is negative if an electromagnetic field is induced between the two ends when it is moved through an illustrated magnetic field. Explain how the emf is produced in the rod. (c) Explain how the principle of induction can be used to heat a conductor.

### Question 27

Section I Question 27 - 2002 HSC

Discuss how energy savings can be achieved by the use of superconductors in the areas of electricity generation and transmission, and transportation.