Induction and Transformers

Question 1

What do transformers do?

Answer 1

They use electromagnetic induction to change voltage by using an alternating current.

Question 2

What does a transformer look like and what is a rule for its power?

Answer 2

power in = power out

Therefore, V_PI_P = V_SI_S

Question 3

How does a step-up transformer work?

Answer 3

• A step-up transformer increases the number of turns on the secondary (output) side.
• This increases the voltage on the output side and so decreases the current.
• Less heat is produced ⇒ less energy wasted (and dissipated into the atmosphere).

Question 4

How does a step-down transformer work?

Answer 4

• A step down tranformer increases the number of turns on the primary (input) side.
• This decreases the voltage on the output side so increases the current.
• Voltage is reduced and therefore safer to use.

Question 5

What is the transformer equation linking the number of turns and voltage?

Answer 5

N = number of turns

V = voltage

_P = primary side

_S = secondary side

• N_p÷N_S = V_P÷V_S

Question 6

Why are step-down transformers useful?

Answer 6

They reduce the voltage when electricity is entering homes and factories so it is safer to use.

Question 7

Why are step-up transformers useful?

Answer 7

They reduce the current, so reduce the amount of energy lost as heat and make transmitting mains electricity more efficient.

Question 8

How is electricity generated by the rotation of a magnet in a coil of wire?

Answer 8

• When a magnet moves into a coil, there is an increase in the number of magnetic field lines cutting through the coil.
• This change causes voltage to be induced across the ends of the coil.
• As the coil forms a complete circuit, there is also a current induced.

Question 9

Which factors affect the size of induced voltage when a magnet is rotated within a coil?

Answer 9

• A stronger magnet means more field lines and hence a larger voltage is induced.
• If there are more turns of wire around the coil then there will be a greater change in the number of magnetic field lines and a larger voltage is induced.
• If the magnet moves into the coil more quickly, then this will induce a larger voltage.