Transformer

Question 1

A transformer is used to change the:

Accepted Answer

voltage of an AC supply — A transformer raises or lowers the voltage of alternating current.

Question 2

A transformer will NOT work with:

Accepted Answer

steady direct current — Steady DC produces no changing field, so no voltage is induced in the secondary coil.

Question 3

In a step-up transformer, the secondary coil has:

Accepted Answer

more turns than the primary — More secondary turns give a higher output voltage, so the transformer steps up.

Question 4

The core of a transformer is usually made of:

Accepted Answer

soft iron — A soft iron core links the changing magnetic field between the two coils.

Question 5

Which equation is correct for an ideal transformer?

Accepted Answer

Vs ÷ Vp = Ns ÷ Np — For an ideal transformer the voltage ratio equals the turns ratio.

Question 6

A transformer has Vp = 240 V, Np = 1200 turns and Ns = 100 turns. Vs is:

Accepted Answer

20 V — Vs = 240 × (100 ÷ 1200) = 20 V.

Question 7

For an ideal transformer, the power in the primary coil compared with the secondary coil is:

Accepted Answer

equal — An ideal transformer wastes no energy, so power in equals power out.

Question 8

When a step-up transformer raises the voltage, the output current is:

Accepted Answer

lower than the input — Because power is conserved, raising voltage lowers the current by the same factor.

Question 9

The coil that receives the input voltage is called the:

Accepted Answer

primary coil — The primary coil receives the input; the secondary gives the output.

Question 10

A step-down transformer is used to:

Accepted Answer

decrease the voltage — A step-down transformer has fewer secondary turns, so it lowers the voltage.