6.11 Electromagnetism

Question 1

What is the role of transformers?

Answer 1

Change the size of voltage for an alternating current

Question 2

How do transformers work?

Answer 2

• AC flowing in primary coil induces an alternating magnetic field /flux
• The alternating magnetic field passes through thr iron core to the secondary coil
• The change in magnetic flux induces and alternating emf/voltage in the secondary coil of equal frequency

Question 3

How can the voltage and number of turns on each side of a transformer be derived? (Faradays law)

Answer 3

We know V1=-N1(dfeta/dt) and V2=-N2(dfeta/dt)
So for 100% efficiency
V1/V2=N1/N2

Question 4

How current and no of turns be linked for an ideal transformer?

Answer 4

Power in=power out
I1xV1=I2xV2
V1/V2=I2/I1

Question 5

What is a step up transformer?

Answer 5

Transformer with more turns on secondary coil to increase voltage

Question 6

What is a step down transformer?

Answer 6

Transformer with fewer turns on secondary coil to decrease voltage

Question 7

How can the efficiency of a transformer be increased (two ways)?

Answer 7

Laminations in iron core to reduce efefct of eddy currents

Thick copper wires as have low resistance so less heat transfered through wires

Question 8

What are eddy currents?

Answer 8

Tiny currents induced by changing magnetic flux in iron core

Question 9

What direction do flux lines go.?

Answer 9

North to south