Electromagnets

Question 1

in terms of magnetism what occurs when a current flows through a wire and the properties of the occurrence

Answer 1

it creates a circular magnetic field around the wire. The magnetic field can deflect the needle of a magnetic compass

Question 2

How is the magnetic field generated by current’s strength increased

Answer 2

move it closer to the wire

if the current is increased

Question 3

solenoid

Answer 3

A solenoid consists of a wire coiled up into a spiral shape.

Question 4

The motor effect

Answer 4

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.

Question 5

Calculating the motor force force = magnetic flux density × current × length

READ IT AND UNDERSTAND

Answer 5

force = magnetic flux density × current × length

Question 6

F is force in newtons (N)

B is magnetic flux density (magnetic field strength) in
tesla (T)

I is current in amperes - also

referred to as amps (A)
is length in metres (m)

Answer 6

force = magnetic flux density × current × length

Question 7

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

Answer 7

the current in the wire increases

the strength of the magnetic field increases

Question 8

what is the motor effect when current and magnetic field are parallel with each other

Answer 8

non existant

Question 9

How can an electric motor be created

Answer 9

A coil of wire carrying a current in a magnetic field experiences a force that tends to make it rotate. This effect can be used to make an electric motor.

Question 10

What two features of a DC motor allow the coil to continue rotating even though it moves parallel to the magnetic field

Answer 10

the momentum of the motor carries it on round a little

a split ring commutator changes the current direction every half turn

Question 11

What happens once the conducting brushes reconnect with the commutator after a half turn

Answer 11

current flows in the opposite direction through the wire in the coil

each side of the coil is now near the opposite magnetic pole

Question 12

How does alternating current supplied to a loudspeaker create sound waves through a speaker

Answer 12

1. a current in the coil creates an electromagnetic field
2. the electromagnetic field interacts with the permanent magnet generating a force, which pushes the cone outwards
3. the current is made to flow in the opposite direction
4. the direction of the electromagnetic field reverses
5. the force on the cone now pulls it back in
6. repeatedly alternating the current direction makes the cone vibrate in and out
7. the cone vibrations cause pressure variations in the air, which are sound waves