P7: TRANSFORMERS

Question 1

What is a transformer?

Answer 1

a device that can change the pd/voltage of an alternating current

Question 2

What does a step-up transformer do?

Answer 2

-increases voltage, decreases current
(-to reduce energy being lost as heat)

Question 3

What does a step-down transformer do?

Answer 3

-decreases voltage, increases current
-for safety reasons

Question 4

How do transformers work?

Answer 4

-primary voltage drives an alternating current through the primary coil
-the primary coil current produces a magnetic field, which changes as the current changes
-the iron core increases the strength of the magnetic field
-the changing magnetic field induces a changing potential difference in the secondary coil
-the induced potential difference produces an alternating current in the external circuit

Question 5

How do step-up transformers increase pd?

Answer 5

more turns on secondary coil (compared to primary coil)

Question 6

How do step-down transformers decrease pd?

Answer 6

more turns on primary coil (compared to secondary coil)

Question 7

What is the equation linking pd in primary coil, pd in secondary coil, no. of coils in primary coil and no. of coils in secondary coil?

Answer 7

pd in primary coil (V) / pd in secondary coil(V) = no. of coils in primary coil / no. of coils in secondary coil (Vp/Vs = Np/Ns)

Question 8

Why does Vp/Vs = Np/Ns?

Answer 8

because the ratio between the primary and the secondary pds is the same as the ratio between the no. of turns on the primary and secondary coils