Magnetism

Question 1

Describe 2 ways you can find the shape of a magnetic field

Answer 1

Iron filings
Plotting compasses

Question 2

Name 2 electrical devices that use magnets

Answer 2

Motors
Loudspeakers

Question 3

Magnetic field lines point from ——— to ———- ?

Answer 3

North to south

Question 4

Where is the field strongest

Answer 4

Where the lines are closest together

Question 5

Name 3 magnetic elements

Answer 5

Iron cobalt nickel

Question 6

What is an induced magnet

Answer 6

A magnet which is only a magnet because it is in the field of another magnet

Question 7

What is a solenoid

Answer 7

A coil with a current flowing through it

Question 8

Name the 3 things that affect the strength of an electromagnet

Answer 8

Number of turns on coil
Size of electric current through coil
Material of core

Question 9

What shape is a magnetic field around a wire with a current flowing through it

Answer 9

Circular

Question 10

Where is the field strongest on an electromagnet

Answer 10

Down the middle
(It is also uniform down the middle)

Question 11

What rule gives the direction of the magnetic field around the wire

Answer 11

The right hand thumb rule
(Thumb being direction of current)

Question 12

What rule gives the direction of force felt

Answer 12

Flemings left hand rule
(Third finger is current and thumb is force)

Question 13

What are the 3 elements other than the magnet needed for an electric motor

Answer 13

Dc supply
Commutator
Brushes

Question 14

How does an electric motor change the polarity of the electromagnet

Answer 14

When the brushes pass from one plate on the commutator to the other (gaps) this causes a polarity switch

Question 15

Describe method using plotting compass to find the magnetic field of a magnet

Answer 15

1. Place plotting compasses near the magnet on a piece of paper
2. Mark the direction the compass needle points
3. Move the plotting compass to many different positions in the magnetic field, marking the direction of the needle each time
4. Join the points to show field lines

Question 16

Describe the motor effect

Answer 16

A wire carrying a current creates a magnetic field.
This can interact with another magnetic field, causing a force that pushes the wire at right angles.
This is called the motor effect

Question 17

When does the force on a given length of wire increase when in a magnetic field

Answer 17

Current in the wire increases
Strength of the magnetic field increases

Question 18

What is a permanent magnet

Answer 18

Poles which are north and south all the time

Question 19

How does a microphone depend on sound and electrical energy

Answer 19

A microphone transfers sound waves into an electrical signal

Question 20

How does a loudspeaker depend on sound and electrical energy

Answer 20

A loudspeaker converts an electrical signal into sound waves

Question 21

How does a microphone work

Answer 21

As the diaphragm moves in and out a varying pd is induced across the ends of the wire, producing a varying electric current
The varying electrical current then travels through the wires until it reaches the loudspeaker

Question 22

How does the diaphragm move in and out in a microphone

Answer 22

The sound wave is made up of areas of high and low pressure
The high pressure areas push the diaphragm in and the low pressure areas cause it to move outwards