Transformers

Question 1

What do transformers use to change potential difference?

Answer 1

Electromagnetic induction

Question 2

Because transformers use electromagnetic induction to change potential difference, which type of current do they only work with?

Answer 2

AC

alternating current

Question 3

Describe the makeup of a transformer

(4 points)

Answer 3

1. Primary coil on left
2. Secondary coil on right
3. Iron core joining the two coils
4. Magnetic field in the iron core

Question 4

What does a step-up transformer do to the voltage?

Answer 4

It steps it up

(increases it)

Question 5

What do step-down transformers do to the voltage?

Answer 5

They step it down

(decrease it)

Question 6

Which of the coils in a step-up transformer has more turns?

Answer 6

The secondary coil has more turns than the primary

Question 7

Which of the coils in a step-down transformer has more turns?

Answer 7

The primary coil has more turns than the secondary

Question 8

The primary coil produces a ____ ____ which stays within the ____ ____ . This means that nearly all of it passes through the ____ ____ and hardly any is ____ .

Answer 8

The primary coil produces a magnetic field which stays within the iron core. This means that nearly all of it passes through the secondary coil and hardly any is lost.

Question 9

What does the AC in the primary coil do to the magnetic field?

Answer 9

Causes it to constantly change direction - it is a changing magnetic field

Question 10

How many times a second does the magnetic field change direction if the current is at 50Hz?

Answer 10

100 times a second

Question 11

What feels the rapidly changing magnetic field?

Answer 11

The secondary coil

Question 12

What does the changing field induce across the secondary coil?

Answer 12

Alternating potential difference

Question 13

The frequency of the alternating potential difference across the secondary coil is equal to what?

Answer 13

The alternating current across the primary coil

Question 14

What is the only role of the iron core?

Answer 14

Transferring the changing magnetic field from the primary coil to the secondary

Question 15

What is the iron core NOT part of?

Answer 15

The flow of electricity

Question 16

What is voltage a measure of?

Answer 16

Potential difference

Question 17

As voltage measures potential difference, what happens to the potential diffence in a step-up transformer?

Answer 17

The p.d. across the primary coil is less than p.d. across the secondary coil

Question 18

As voltage measures potential difference, what happens to the potential diffence in a step-down transformer?

Answer 18

The p.d. across the primary coil is greater than p.d. across the secondary coil

Question 19

Why wouldn’t you get anything out of a secondary coil if you put direct current into the primary?

Answer 19

The magnetic field in the core would not be constantly changing, so there’d be no induction in the secondary because you need a changing magnetic field to induce a potential difference

Question 20

What is the formula for working out calculating the output potential difference from knowing the input potential difference and the number of turns on each coil?

Answer 20

p.d. across P coil number of turns on P coil

_____________ = ____________________

p.d. across S coil number of turns on S coil

Question 21

What is the algebra formula for working out potential difference/ number of coils etc?

Work it out with the S coil the subject and then with the P coil as the subject

Answer 21

V_s n_p

_{__=__}

V_p n_s

or

V_p n_s

_{__=__}

V_s n_p

Question 22

Work out the output p.d. for a transformer with:

40 turns on primary coil

800 on secondary coil

Input p.d. 1000 V

Answer 22

V_s / V_p = n_s / n_p

V_s / 1000 = 800 / 40

V_s = 1000 x (800/40)

20,000 V