4.7.3.4 Transformers

Question 1

What does a basic transformer consist of?

Answer 1

a primary coil and a secondary coil wound on an iron core

Question 2

Why is iron used as a core in transformers?

Answer 2

as it is easily magnetised

Question 3

What does the ratio of p.d. across the primary and secondary coil in a transformer depend on?

Answer 3

ratio of p.d. across primary and secondary coils of a transformer depends on the ratio of the number of turns on each coil

Question 4

What would happen if transformers were 100% efficient?

Answer 4

if transformers were 100% efficient the electrical power output would equal the electrical power input

Question 5

Transformer diagram:

Answer 5

have same number of turns in primary and secondary coil so if transformer is 100% efficient then the p.d. in the primary coil will equal the p.d. in the secondary coil

Question 6

What is the relationship between the primary and secondary coils in a transformer?

Answer 6

• the 2 coils are completely separate
• there is no way that electrical current can pass directly from one col to another

Question 7

How do transformers work?

Answer 7

• the primary coil is connected to AC supply
• as the current flows through the primary coil it generates a changing magnetic field
• the magnetic field is transmitted along the iron core and passes through the secondary coil
• when the changing magnetic field passes through the secondary coil it induces a p.d.

Question 8

What do iron cores do in transformers?

Answer 8

increases the strength of the magnetic field

Question 9

What do transformers only work with?

Answer 9

• transformers only work with AC as a changing magnetic field is needed to induce a p.d.
• a direct current produces a constant magnetic field and therefore it doesn’t work in transformers

Question 10

Step-up transformer:

Answer 10

Vs > Vp

Question 11

Step-down transformer:

Answer 11

Vp > Vs

Question 12

What does a transformer with more turns in the secondary coil than the primary coil do?

Answer 12

• step-up transformer
• more turns in secondary coil than primary coil so p.d. induced in secondary coil will be greater than the p.d. in the primary coil

Question 13

What does a transformer with fewer turns in the secondary coil than the primary coil do?

Answer 13

• step-down transformer
• fewer turns in secondary coil than primary coil so p.d. induced in secondary coil is less than p.d. in primary coil