P14. Electromagnetic effects

Question 1

structure of a transformer

Answer 1

primary coil
secondary coil
iron core

Question 2

Wire passed across a magnetic field:

Answer 2

a small EMF is induced

➫ EMF causes current

Question 3

“step up” transformer?

Answer 3

Vp < Vs

Question 4

define motor effect (basic)

Answer 4

A (current-carrying) wire or coil can exert a force on a permanent magnet.

Question 5

A.C is applied from a source passes thr primary coil induces A.C in secondary coil

Answer 5

The iron core gets magnetize by the incoming current and this magnetism then creates a current in the leaving wire.

Question 6

left hand rule

Answer 6

first finger : field
second finger : current
thumb: movement

Question 7

describe the motor effects with dc

Answer 7

➫ A DC motor runs on a direct current.

➫ The coil is made of insulated copper wire and is free to rotate between the poles of the magnet.

➫ commutator is fixed to the coil n rotates with it.

➫ When the coil overshoots the vertical, the commutator changes direction of the current through it, so the forces change direction and keep the coil turning.

➫ The brushes are two contacts which rub against the commutator and keep the coil connected to battery, usually made of carbon

➫The maximum turning effect is when the coil is horizontal.

➫There is no force when the coil is vertical but it always overshoots this position

Question 8

COMMUTER

left hand rule related

Answer 8

Speakers
permanent magnet +electromagnet
* two poles of the permanent magnet remain the same,
✳✳when direction of electric current reverses
➫ poles of electromagnet reverse

1 same end of the electromagnet becomes N poles
➫ electromagnet N pole 💓 permanent S pole
pulls electromagnet toward permanent magnet

2.commuter changes current direction,
➫same end of electromagnet becomes N pole.
➫electromagnet is repelled by the S pole of permanent ➫ moves away

➫ speaker cone is connected to the electromagnet
➫ speaker moves
➫ creates vibrations in the air

Question 9

define motor effects

Answer 9

If a wire carrying a current is placed in a magnetic field a force is produced.

Question 10

State the two main ways to generate electricity.

Answer 10

moving a magnet in a coil of wire

moving a wire in a magnetic field