Electromagnetism

Question 1

why is an alternating pd required for a transformer to work

Answer 1

alternating pd produces an alternating magnetic field. Transformers won’t work with a direct pd as the magnetic field lines won’t change direction

Question 2

why is the core of a transformer made of iron

Answer 2

it’s magnetic

Question 3

describe how a transformer works

Answer 3

• Alternating pd or current is needed in PC
• This induces a changing magnetic field
• this in turn gives a changing magnetic field in SC
• This induces an alternating pd in the SC

Question 4

describe the motor effect

Answer 4

a wire with a current flowing through it has a magnetic field around it. when in a permanent magnetic field, the two fields interact and a force results. a wire parallel to the permanent field lines will experience

Question 5

2 ways of increasing force in motor effect

Answer 5

increase the current

increase strength of magnet

Question 6

how is the motor effect reversed

Answer 6

change the direction of the current or reverse the polarity

Question 7

lighter smaller transformer

Answer 7

switch mode

Question 8

2 advantages of a switch mode transformer

Answer 8

• lighter, smaller and more portable

* draws little power when no load is applied

Question 9

material that make up a transformer

Answer 9

iron core
copper wire (insulated)

Question 10

difference between step up and step down transformers

Answer 10

step up- more turns on the SC creating a bigger output

step down- more turns on PC creating a small output

Question 11

where can you find a switch mode transformer

Answer 11

in mobile phone chargers etc

Question 12

how do you find the direction of a force in the motor effect

Answer 12

use Flemings left hand rule:
•first finger=magnetic field
•second finger= current
•thumb=direction of the force

Question 13

how is PD induced across a conductor

Answer 13

if the conductor (the coil) cuts through a magnetic field

Question 14

when power output and input of a transformer are the same, what can we say about the transformer

Answer 14

it is 100% efficient

Question 15

frequency of a switch mode transformer

Answer 15

between 50kHz and 200kHz

Question 16

why is the wire in a coil wrought core of a transformer coated in plastic

Answer 16

plastic is an insulator, preventing current flowing through the core. this prevents a short circuit