# 7.1 Magnetism and electromagnetism - Low demand - Qs 2019-05-10آ  Page 1 of 20 7.1 Magnetism and electromagnetism

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7.1 Magnetism and electromagnetism – Low demand – Questions

Q1. The left-hand rule can be used to identify the direction of the force acting on a current-carrying conductor in a magnetic field.

(a) Use words from the box to label Figure 1.

current field force potential difference

(3)

(b) Figure 2 shows an electric motor.

(i) Draw an arrow on Figure 2 to show the direction of the force acting on the wire AB.

(1)

(ii) Suggest two changes that would increase the force acting on the wire AB.

1. ____________________________________________________________

2. ____________________________________________________________ (2)

(iii) Suggest two changes that would reverse the direction of the force acting on

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the wire AB.

1. ____________________________________________________________

2. ____________________________________________________________ (2)

(c) A student used an electric motor to lift a mass. This is shown in Figure 3.

The student varied the electrical input power to the motor. For each different electrical input power, he recorded the time taken to lift the mass and calculated the output power of the motor.

The results are shown in the table.

Test Electrical

input power in watts

Work done lifting the

mass in joules

Time taken to lift the mass in seconds

Output power

in watts

A 20 24 2.4 10

B 40 24 1.2 20

C 60 24 0.8 30

D 80 24 0.2 120

The result for Test D is anomalous.

(i) Calculate the efficiency of the motor in Test D.

______________________________________________________________

______________________________________________________________

Efficiency = ____________________ (2)

______________________________________________________________

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______________________________________________________________ (1)

(iii) Suggest a reason for this anomalous result.

______________________________________________________________

______________________________________________________________ (1)

(Total 12 marks)

Q2. Figure 1 shows the magnetic field around a copper wire carrying a current.

Figure 1

(a) What do the arrows on the magnetic field line represent?

___________________________________________________________________

___________________________________________________________________ (1)

(b) Complete the sentence.

Choose the answer from the box.

decreases increases stays the same

As the distance from the copper wire increases, the

magnetic field strength ____________________ . (1)

(c) Suggest how the field lines on Figure 1 show the variation in field strength.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________ (2)

A student coiled the copper wire a different number of times to form a solenoid.

Each time the student measured the strength of the magnetic field inside the solenoid.

Figure 2 shows the results.

Figure 2

(d) Draw a line of best fit on Figure 2. (1)

(e) Determine the increase in strength of magnetic field when the number of turns on the coil is changed from 12 to 18

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

Increase in strength of magnetic field = ____________________ arbitrary units (2)

(f) How could the strength of the magnetic field be increased?

Tick two boxes.

Increase the current through the solenoid.

Increase the potential difference across the solenoid.

Increase the temperature of the solenoid.

Spread the turns of wire on the solenoid further apart.

Use wire with a higher resistance to make

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the solenoid.

(2)

(g) Figure 3 shows the north and south poles of a solenoid.

Figure 3

Draw field lines to show the magnetic field around the solenoid. (2)

(h) How can the solenoid be made into an electromagnet?

___________________________________________________________________

___________________________________________________________________ (1)

(Total 12 marks)

Q3. A magnetic toy uses ring-shaped magnets.

Look at Figure 1.

The magnets can move up and down the rod. Ring magnet B appears to float.

Figure 1

(a) The magnetic poles are labelled on ring magnet A.

Label the magnetic poles on ring magnet B. (1)

(b) What would happen if ring magnet B was turned upside down?

___________________________________________________________________

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___________________________________________________________________ (1)

(c) Figure 2 shows four plotting compasses arranged around a wire.

The needle of a compass is a magnet.

Figure 2

In Figure 2 the switch is open and there is no current in the wire.

Explain why the compass needles all point in the same direction.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(d) Figure 3 shows the switch closed.

Figure 3

There is now a current in the wire.

The compass needles change direction.

On Figure 3 draw arrowheads on the three incomplete compass needles to show

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their direction. (1)

(e) What would happen to the direction of the compass needles if the current was reversed?

___________________________________________________________________

___________________________________________________________________ (1)

(f) Figure 4 shows a coil of wire in a circuit.

Figure 4

On Figure 4 draw the magnetic field due to the current in the coil. (3)

(Total 9 marks)

Q4. The area around a magnet is called the magnetic field.

(a) The Earth has a magnetic field.

What causes the Earth’s magnetic field?

Tick one box.

The movement of liquid iron in the Earth’s outer core

The gravitational field of the Earth

The permanent magnet in the Earth’s core

(1)

(b) Look at Figure 1.

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Figure 1

Opposite poles brought together

Same poles brought together

What will happen in each case when the poles of two magnets are brought close together?

Opposite poles brought together _______________________________________

___________________________________________________________________

Same poles brought together __________________________________________

___________________________________________________________________ (2)

(c) Figure 2 shows an electromagnet being used to lift a car in a scrapyard.

Figure 2

An electromagnet is a solenoid.

Explain why it is better to use an electromagnet rather than a permanent magnet in a scrapyard.

You should include a comparison of the properties of electromagnets and permanent magnets in your answer.

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(Total 7 marks)

Q5. A student has made a simple electric motor. The diagram shows the electric motor.

(a) Complete the following sentence by drawing a ring around the correct line in the box.

the cell

Once the coil is spinning, one side of the coil is pushed by the coil and

a force

the other side is pulled, so the coil continues to spin. (1)

(b) Suggest two changes to the electric motor, each one of which would make the coil spin faster.

1. _________________________________________________________________

___________________________________________________________________

2. _________________________________________________________________

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