magnetism - transformers

Question 1

how are transformers used to change the potential difference of an electricity supply?

Answer 1

• primary coil is connected to an alternating current. as current flows through the primary coil, it generates a changing magnetic field.
• this magnetic field is transmitted along the iron core and passes through the secondary coil. when changing magnetic field passes through secondary coil, it induces a potential difference

Question 2

what is the structure of a transformer?

Answer 2

consists of 2 coils of wire. on the left, the primary coil and on the right the secondary coil. these are separate and there is no way electrical current can pass directly from one coil to another. 2 coils are wrapped around an iron core. iron is used as it is easily magnetised

Question 3

what does the iron core in a transformer do?

Answer 3

iron core increases the strength of the magnetic field

Question 4

when do transformers only work?

Answer 4

with alternating current. That is because we need a changing magnetic field to induce a potential difference. A direct current produces a constant magnetic field and therefore it does not work in transformers

Question 5

what does it mean when a transformer coils (primary and secondary) have the same number of coils?

Answer 5

the potential difference in the secondary coil will be the same as the p.d in the primary coil. This is only the case if the transformer is 100% efficient (no energy wasted). In practice transformers aren’t 100% efficient

Question 6

step up transformer

Answer 6

• more turns in the secondary coil than in primary. this means p.d induced in secondary coil will be greater than primary coil
• known as ‘step up’ transformer as it ‘steps up’ the p.d
• depending on transformer the secondary coil can have twice the number of turns to primary coil which means the p.d in the secondary coil will be twice the p.d in the primary coil

Question 7

step down transformer

Answer 7

• fewer turns in secondary coil compared to primary coil
• p.d in the secondary coil is less than the p.d in the primary coil
• if in the example, the secondary coil has half the number of turns as the primary coil then the secondary coil will be half the p.d in the primary coil