Electromagnetic Induction In Transformers

Question 1

what is electromagnetic induction

Answer 1

the induction of a potential difference (and current if there is a complete circuit) in a wire which is experiencing a change in magnetic field

Question 2

what is the first situation in which you can get electromagnetic induction

Answer 2

if an electric conductor and a magnetic field move relative to each other

Question 3

how can you make an electric conductor (coil of wire) and a magnetic field move relative to each other

Answer 3

• by rotating or moving a magnet in a coil of wire

- or moving a conductor in a magnetic field

Question 4

what is the effect of moving a magnet or conductor in the opposite direction to where it was originally rotating or moving in the presence of the other

Answer 4

the potential difference and current will be reversed

Question 5

how do you produce an alternating current when moving an electric conductor and magnetic field relative to each other

Answer 5

• by keeping the magnet moving backwards and forwards

- or keeping it rotating in the same direction

Question 6

how can you get an induced potential difference

Answer 6

when the magnetic field through an electrical conductor changes (gets bigger, smaller or reverses)

Question 7

what are the three ways that you can increase the size of an induced potential difference

Answer 7

• by increasing the strength of the magnetic field
• increasing the speed of movement or change of the field
• or having more turns per unit of length on the coil of wire

Question 8

why does an induced pd or current always oppose the change that made it

Answer 8

• when a current is induced in a wire, the current produces its own magnetic field
• the magnetic field created by an induced current always acts against the change that made it
• its basically trying to return things to the way they were

Question 9

why do transformers use induction

Answer 9

to change the size of a potential difference in an alternating current

Question 10

what do all transformers have

Answer 10

• two coils of wire
• a primary and a secondary coil
• joined with an iron core

Question 11

what happens when an alternating potential difference is produced across the primary coils in a transformer

Answer 11

the primary coils produce an alternating magnetic field

Question 12

what is the iron core of a transformer

Answer 12

a core of magnetic material that is easily magnetised and demagnetised

Question 13

what is the effect of the primary coils producing an alternating magnetic field when next to the iron core

Answer 13

• the magnetisation of the iron core also alternates

- and the changing magnetic field induces a pd in the secondary coil

Question 14

what do step up transformers do and what do they have

Answer 14

• they step the potential difference up

- they have more turns in the secondary coil than in the primary coil

Question 15

what do step down transformers do and what do they have

Answer 15

• they step the potential difference down

- they have more turns in the primary coil than in the secondary coil

Question 16

what is the efficiency of a transformer and what does it allow you to assume

Answer 16

• their efficiency is 100%

- which allows you to assume that the input power is equal to the output power

Question 17

what is the equation for working out the input and output power of transformers and why does it make sense

Answer 17

• Vp x Ip = Vs x Is
• potential difference across primary coil x current through primary coil = potential difference across secondary coil x current through secondary coil
• it makes sense as the efficiency of transformers is 100%
• so you can assume that the input and output power is the same
• and P = IV so all you’re saying is IV of primary coil = IV of secondary coil