P3.3 Keeping things moving

Question 1

What happens when a current flows through a wire?

Answer 1

A magnetic field is produced around the wire

Question 2

Give three uses of electromagnets

Answer 2

Cranes to lift/drop iron/steel
Loudspeaker
Electric bell

Question 3

What is (are the principles of) the motor effect?

Answer 3

When a wire CARRYING A CURRENT in a magnetic field experiences a force

Question 4

How can the size of the force be increased?

Answer 4

Inc. strength of the magnetic field

Inc. the size of the current

Question 5

When will the conductor (wire) not experience a force?

Answer 5

If it is parallel to the magnetic field

Question 6

What are the two ways that you can reverse the force?

Answer 6

• Direction of the current is reversed

- Direction of the magnetic field is reversed

Question 7

What does each finger represent in Fleming’s left-hand rule?

Answer 7

thuMb=Movement/motion (force)
First Finger= Field
seCond finger= Current

Question 8

In what direction is a magnetic field in?

Answer 8

From the North to South poles

Question 9

What happens if an electrical conductor ‘cuts’ through a magnetic field?

Answer 9

A p.d. is induced across the ends of the CONDUCTOR

Question 10

What happens if a magnet is moved into a coil of wire?

Answer 10

A p.d. is induced across the ends of the COILS

Question 11

Describe the basic structure of a transformer

Answer 11

• Soft iron core
• Two coils of insulated wire wrapped separately around it
• Each coil has a different number of coils/turns/loops

Question 12

What is the primary coil connected to and what does it act as?

Answer 12

Connected to an A.C. supply

Acts as an ELECTROMAGNET

Question 13

What happens at the secondary coil?

Answer 13

-An alternating p.d. is induced

Question 14

How do transformers work? (5/6 mark question)

Answer 14

• A.C. through primary
• Makes a mag. field (that continuously changes direction)
• Core inc. field strength
• Secondary cuts through field
• Induces an alternating p.d. across the ends of the coil

Question 15

When does an a.c. flow?

Answer 15

When the circuit is connected to the secondary coil

Question 16

What is the core of a transformer made from?

Answer 16

It’s a soft iron core

Question 17

Why does the primary coil only work on an a.c. current?

Answer 17

Because a.c. causes a constantly changing mag. field which will induce a.c. in secondary

Question 18

If the primary has 6 coils and the secondary has 12, what type of transformer is it?

Answer 18

Step-UP

Question 19

What is the definition of a step-down transformer in terms of potential difference?

Answer 19

When the P.D. across SECONDARY is LESS THAN the p.d. across the PRIMARY

Question 20

How would a transformer be 100% efficient?

Answer 20

If the electrical POWER OUTPUT would EQUAL the electrical power INPUT

Question 21

At what frequency do switch-mode transformers work at?

Answer 21

Between 50 kHz and 200 kHz