P15 - Transformers

Question 1

transformer

Answer 1

changes size of alternating PD from 230 v to battery pd

Question 2

step up -

Answer 2

increases size of alternating PD

Question 3

step down

Answer 3

decreases size of alternating PD

Question 4

how it works

Answer 4

2 coils of insulated wire
-both wound aorund iron core

Question 5

why is iron used

Answer 5

easily magnetised /demagnetised

Question 6

primary coil

Answer 6

connected to ac supply

Question 7

secondary coil

Answer 7

as ac passes - alternating pd is induced here

Question 8

why is alternating pd induced

Answer 8

ac passes through primary coil
- generates alternating mg field in iron core
- lines of alternating mg field in core pass through secondary coil
- mg in secondary induces alternating pd

Question 9

if secondary coil is attached to bulb in a complete circuit

Answer 9

• induced pd
  = ac so bulb lights up

Question 10

energy is transferred from

Answer 10

primary to secondary
-despite not being electrically connected

Question 11

practical transformers

Answer 11

only works with ac
- with dc - no change in mg field so secondary ac is 0

Question 12

step up - coils

Answer 12

more turns in secondary than primary

Question 13

step down - coils

Answer 13

• more in primary than secondary

Question 14

formula for Vp/Vs =

Answer 14

Np/Ns

Question 15

if 100% efficient formula

Answer 15

P PD x P I = S PD x S I

Question 16

step up transformer - pd

Answer 16

pd is raised
-current is lowered

Question 17

why is current lowered

Answer 17

heating effect is smaller
-less power is wasted

Question 18

if pd increases and current decreases

Answer 18

same amount of power
-less wasted due to heating effect
-more efficient

Question 19

heating effect is directly proportional to

Answer 19

I^2
current ^2