4B Electromagnetic effects WB

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4B Core

1) Choose the correct answer. An e.m.f. is induced in a conductor when it:

1 point

A moves parallel to magnetic field lines

B moves across magnetic field lines

C is at rest in a magnetic field

D is heated in the absence of a magnetic field.

Clear selection

2) An electromagnet is constructed by winding a solenoid on a soft iron core. Give two ways by which the strength of the electromagnet could be increased.

2 points

smaller current

larger current

less turns on solenoid

more turns on solenoid

3) When a coil is rotated in a magnetic field, an e.m.f. is generated. Choose the incorrect answer.

1 point

A the speed of the coil increases

B the number of turns on the coil decreases

C the strength of the magnetic field increases.

Clear selection

4) Describe the field around a current-carrying straight wire, describing the direction of the current and of the field lines.

3 points

5) A current-carrying straight wire is placed between the poles of a magnet, as shown. The wire moves downwards when current flows.

5) a) State the direction in which the wire moves when the current direction is reversed.

1 point

Right

Left

Upwards

Downwards

Clear selection

5) b) State the direction in which the wire moves when the magnetic field direction is reversed.

1 point

Right

Left

Upwards

Downwards

Clear selection

6) Explain why electricity is distributed around the country using a.c. rather than d.c.

2 points

7) Choose the correct answer.The main function of a step-up transformer is to:

1 point

A increase power

B increase current

C increase voltage

D decrease resistance of a circuit.

Clear selection

8) 240V a.c. is applied to the primary coil of a transformer which has 600 turns. The secondary coil has 30 turns.

8) a) Calculate the p.d. across the secondary coil. Record your working.

3 points

8) b) State the type of transformer.

1 point

Step-up

Step-down

Clear selection

4B Supplement

9) A bar magnet is moved in and out of a coil that is connected to a sensitive centre-zero meter, as shown. The meter needle swings to the left when the magnet is moving towards the coil. State how the needle behaves when the bar magnet:

9) a) is at rest inside the coil

1 point

swings further to the left

swings to the left

does not move

swings to the right

swings further to the right

Clear selection

9) b) is moving back out of the coil

1 point

swings further to the left

swings to the left

does not move

swings to the right

swings further to the right

Clear selection

9) c) moves more quickly towards the coil

2 points

swings further to the left

swings to the left

does not move

swings to the right

swings further to the right

Clear selection

9) d) is at rest and the coil is moved away from the magnet.

2 points

swings further to the left

swings to the left

does not move

swings to the right

swings further to the right

Clear selection

10) A straight wire is moved upwards through a horizontal magnetic field. State the direction in which current will flow in the wire if it is connected to a complete circuit.

1 point

current flows to the left

current flows to the right

Clear selection

11) A bar magnet is moved towards a coil of wire connected to a meter, as shown. An e.m.f. is induced in the coil and current flows in the circuit making the coil act like a magnet. State the polarity of the end of the coil nearest the magnet when the N pole of the magnet:

11) a) approaches the coil

1 point

North pole

South pole

Clear selection

11) b) is pulled back from the coil

1 point

North pole

South pole

Clear selection

11) c) is at rest and the coil is moved towards the magnet.

1 point

North pole

South pole

Clear selection

12) Electricity transmission lines deliver 80kW of power to the consumer at a voltage of 400000V. The resistance of the transmission lines is 15Ω.

12) a) Calculate the current in the transmission lines. Record your working.

1 point

12) b) Calculate the rate of loss of energy from the transmission lines. Record your working.

1 point

13) The pattern of magnetic field lines in and around a solenoid is shown below.

13) a) A solenoid, like a bar magnet, has a N and a S pole.

13) a) i) Is position A or B nearest to the S pole of the solenoid?

1 point

Clear selection

13) a) ii) Explain how the polarity of the solenoid could be reversed.

1 point

13) a) iii) In which direction would the N pole of a plotting compass point if placed at A?

1 point

Left

Right

Clear selection

13) b) State where the magnetic field is:

13) b) i) strong

1 point

Inside the solenoid

Outside the solenoid

Clear selection

13) b) ii) weak

1 point

Inside the solenoid

Outside the solenoid

Clear selection

14) The current in the primary coil of a step-down transformer is 0.15A. The input to the primary coil is 240V and the output from the secondary coil is 12V. Calculate and record your working for the current that can be drawn from the secondary coil if the transformer is:

14) a) 100% efficient in transferring power

3 points

14) b) 90% efficient in transferring power.

2 points

15) A high-speed electron beam enters a region of uniform electric field, produced by a p.d. applied to two parallel metal plates, as shown. In which direction are the electrons deflected?

1 point