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GCSE Level Questions: Magnets and Electromagnets

Q5. (a) The diagram shows a bar magnet. Each yellow-filled circle represents a compass.

Both arrows need to be correct for you to get the mark. Remember a compass arrow points in the direction of the magnetic field lines and they flow from the north pole to the south pole.

See here for more details.

Draw an arrow inside each circle to show the direction that each compass would point.

[1 mark]

(b) The diagram below shows part of a coat. The coat has two magnets hidden inside the material. It indicates how the magnets are used to fasten the coat.

 

Explain why the magnets inside the coat must not have two south poles facing each other.

Like magnetic poles repel each other so two south poles would push the fabric pieces they were attached to apart and the coat would not be held together.

[2 marks]

(c) A coil of wire is connected to a battery. The current in the coil produces a magnetic field.

Which of the following diagrams correctly shows the magnetic field produced by the current in the coil?

[1 mark]

(d) A solid rod is placed inside the coil. Which of the following types of rod would make the magnetic field of the coil stronger? Tick your choice.

Glass rod  
Plastic rod  
Steel rod
Wooden rod  

[1 mark]

(e) Willow investigated how the strength of an electromagnet varied with the current flowing in the coil of the electromagnet. Here is a diagram of the equipment she used.

(i) Why does the spring get longer when the electromagnet is switched on?

The iron bar is attracted by the electromagnet exerts an attractive force on it and pulls at the spring.

[1 mark]

(ii) Willow measured how much further the spring extended with different values of current in the coil. Here is a graph of her results:

The current in the coil is increased from 0.6 A to 1.2 A

Determine the increase in the extension of the spring.

3.0 cm - 1.5 cm = 1.5 cm

[1 mark]

(iii) Calculate the increase in the force on the spring when the current in the coil increased from 0.6 A to 1.2 A - given that the spring constant = 0.18 N/cm.

spring constant = force/extension

0.18 = F/1.5

F = 0.18 x 1.5

F = 0.27 N

[2 marks]

(iv) Describe what happened to the strength of the electromagnet as the current in the coil increased from 1.2 A to 1.6 A

The strength of the electromagnet increases at a decreasing rate until and reaches a maximum steady value at 1.4 A.

[2 marks]

(TOTAL 11 marks)