Chapter 21 & 22 - Electromagnetism

Question 1

Name the type of transformer that converts a low-voltage supply into a high-voltage supply.

Answer 1

step up transformer

Question 2

True or false? Switch mode transformers use very little power when they are switched on but no load is applied.

Answer 2

True

Question 3

Does a step-down transformer increase or decrease the voltage?

Answer 3

Decrease

Question 4

This is the national grid. Label Part 1

Answer 4

Step up Transformer

Question 5

Use for electromagnets

Answer 5

Electromagnets are often used to lift iron and steel scrap in scrapyards.

Question 6

Are electromagnets a type of permenant magnet?

Question 7

A TV requires a potential difference of 11.5V and a current of 10A. It uses a transformer to produce the correct potential difference from the mains supply. If the mains supply is 230V, what current does it provide to the transformer?

Answer 7

0.5A

Question 8

Answer 8

• D
• A parallel field

Question 9

Explain how to produce a uniform magnetic field (3)

Answer 9

• Two permenant bar magnets
• Pole pieces arranged correctly e.g north facing south
• make sure magnets are the correct distance apart

Question 10

When a plastic rod is rubbed with a cloth, the plastic rod gains ……..

After the plastic rod has been rubbed with the cloth, the plastic rod has a …….. charge

Answer 10

electrons

negative

Question 11

Electrostatic charges can be useful during paint spraying.

The droplets of paint are given the same charge as they leave the sprayer.

Explain why this is an advantage (2)

Answer 11

• Repel each other
• Droplets spread out

Question 12

Droplets of paint are positivly charged.

The object being painted is given a negative charge.

Explain why this is an advantage. (2)

Answer 12

• Object attracts droplets
• Less paint wasted

Question 13

Give one hazard caused by electrostatic charges and state how the risk from this hazard can be reduced (2)

Answer 13

• risk of spark/shock/damage
• reduce the risk by using insulation/earthing

Question 15

Describe how a loudspeaker uses an electrical supply to produce sound waves [5 marks]

Answer 15

• There is current in the coil
• changing current produces magnetic field
• Interacts with field of permanent magnet
• Using Fleming’s LHR;
• Force on coil
• Making longitudinal waves

Question 16

State why a metal plate used in an electromagnet device is made of iron (1)

Answer 16

• iron loses its magnetism quickly (not a permenant magnet)

Question 17

Describe the construction of an electromagnet. You may draw a diagram to help your answer. (3)

Answer 17

• current carrying (insulated) wire
• wrapped into coil
• wrapped on iron core;

Question 18

Describe the changes that allow the electromagnet to release the door when the fire alarm sounds (2)

Answer 18

• current/ voltage reduces
• (magnetic) force holding the iron plate to the magnet no longer present