Transformers

Question 1

What are the two main types of transformers?

Answer 1

Step up and step down

Question 2

What do both types of transformer have?

Answer 2

À primary coil and a secondary coil joined with an iron core

Question 3

What is a step up transformer?

Answer 3

It steps the voltage up

They have more turns on the secondary coil than the primary coil

Question 4

What does a step down transformer do?

Answer 4

Step the voltage down

They have more turns on the primary coil than the secondary

Question 5

What does the primary coil produce?

Answer 5

An electromagnetic field which stays within the iron core meaning nearly all of it passes into the secondary coil without being lost

Question 6

What type of current is there in the primary coil and How does this affect the iron core?

Answer 6

Alternating current

Means the field in the iron core is constantly changing direction (it’s a changing magnetic field)

Question 7

Once the rapidly changing magnetic field is felt by the secondary coil what happens?

Answer 7

The changing field induces an alternating potential difference across the secondary coil (same frequency as AC in primary)

Electromagnetic induction of a potential difference

Question 8

What determines whether the potential difference induced in the secondary coil is greater or less than the potential difference in the primary coil?

Answer 8

The number of relative turns on the two coils

Question 9

In a step up transformer where is the PD greater?

Answer 9

PD across the secondary coil is greater

Question 10

In a step down transformer where is the PD greater?

Answer 10

Across the primary coil

Question 11

What type of current has to be used for transformers to work?

Answer 11

Alternating current

Question 12

What would happen if you supplied DC do the primary coil?

Answer 12

You’d get nothing out of the secondary coil
The magnetic field would not be constantly changing so there would be no induction in the secondary coil because you need a changing field to induce potential difference

Question 13

What does the iron core carry?

Answer 13

Magnetic field

NOT CURRENT

Question 14

What is the iron cores job?

Answer 14

To transfer the changing magnetic field from the primary coil to the secondary

No electricity flows round the iron core

Question 15

How can you calculate the output pd/ the input pd/ the number of turns?

Answer 15

PD across primary coil / PD across secondary coil = number of turns on primary coil / number of turns on secondary coil

Question 16

If transformers are nearly 100% efficient what does this mean?

Answer 16

Power in = power out

Power = current x PD

Question 17

Electrical power input = electrical power output how is this written?

Answer 17

V(P)I(P) = V(S) I(S)

Question 18

What are switch mode transformers?

Answer 18

Transformers that operates at higher frequencies that traditional transformers

Question 19

What frequency do they usually operate at?

Answer 19

between 50kHz and 200 kHz

Question 20

What is the advantage of switch mode transformers operating at a higher frequency?

Answer 20

They can be made much lighter and smaller than traditional transformers that work from a 50Hz mains supply

Question 21

What are they used for?

Answer 21

Mobile phone chargers

Power supplies for laptops

Question 22

Why are switch mode transformers more efficient than other types of transformer?

Answer 22

They use very little power when switched on but ‘ no load’ ( the thing you’re charging) is also applied e.g. Left you’re phone charger plugged in but haven’t attached your phone, very little energy is used