Unit 3 AOS 2 Electric Power Revision

A coil consisting of 20 loops with an area of 10 cm2 is placed in a uniform magnetic field B of strength 0.03 T so that

the plane of the coil is perpendicular to the field direction, as shown in the diagram below.

• 0 Wb

• 3.0 × 10^-5 Wb

• 6.0 × 10^-4 Wb

• 3.0 × 10^-1 Wb

A single loop of wire moves into a uniform magnetic field B of strength 3.5 × 10−4 T over time t = 0.20 s from

point X to point Y, as shown in the diagram below. The area A of the loop is 0.05 m2.

• 0 V

• 3.5 × 10^-6 V

• 8.8 × 10^-5 V

• 8.8 × 10³ V

An ideal transformer has an input DC voltage of 240 V, 2000 turns in the primary coil and 80 turns in the secondary

coil.

The output voltage is closest to

• 0V

• 9.6V

• 6.0 × 10³ V

• 3.8 × 10⁷ V

The mains voltage in a particular part of Australia is AC with a voltage of 240 VRMS.

Which one of the following is closest to the peak-to-peak voltage, Vp – p , for this mains voltage?

• 170V

• 340V

• 480V

• 680V

Electrical power stations are often situated far from the cities that require the power that they generate.

Which one of the following best describes the reason for the high-voltage transmission of electrical energy?

• Transformers can be used to increase the voltage in the cities.

• High voltages reduce the energy losses in the transmission lines.

• High voltages provide the large currents needed for efficient transmission.

• High voltages can reduce the overall total resistance in the transmission lines.

In the diagram to the left, the solid line represents the graph of output EMF, ε, versus time produced by an

AC generator. A single change is made to the AC generator and its operation, and the new graph of output

EMF, ε, versus time is shown as a dashed line.

Which one of the following best describes the change made to the AC generator?

• The area of the coil was doubled.

• The speed of rotation was halved.

• The speed of rotation was doubled

• The number of turns of the wire in the coil was doubled.

The diagram Left shows a bar magnet moving upward into a coil.

Which of the following correctly identifies the direction of the induced current, as viewed from the top of the

coil, and the direction of the magnetic field produced by the induced current inside the coil?

• Current direction:

  clockwise

  Magnetic field direction:

  ↓

• Current direction:

  clockwise

  Magnetic field direction:

  ↑

• Current direction:

  anticlockwise

  Magnetic field direction:

  ↑

• Current direction:

  anticlockwise

  Magnetic field direction:

  ↓

A simple DC generator consists of two magnets that produce a uniform magnetic field, in which a square

loop of wire of 100 turns rotates at constant speed, and a commutator, as shown in the diagram to the left.

Which one of the following best shows the display observed on the oscilloscope?

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• 

A step-down transformer is used to convert 240 VRMS AC to 16 VRMS AC.

Assume that the transformer is ideal.

The ratio of turns in the primary (input) to turns in the secondary (output) is best given by

• 15:1

• 1:15

• 24:1

• 1:24

An electrical generator is shown in the diagram to the left. The generator is turning clockwise.

The voltage between P and Q and the magnetic fl ux through the loop are both graphed as a function of time, with

voltage versus time shown as a solid line and magnetic fl ux versus time shown as a dashed line.

Which one of the following graphs best shows the relationships for this electrical generator?

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