7.2 the motor effect

Question 1

What is produced when current flows
through a conducting wire?

Answer 1

A magnetic field is produced around the
wire

Question 2

What determines the strength of the
magnetic field around a current-carrying
wire?

Answer 2

● The magnitude of the current flowing
through the wire
● The distance from the wire

Question 3

What is a solenoid?

Answer 3

A coil of wire which when current passes
through creates a strong magnetic field

Question 4

Describe the magnetic field found inside
a solenoid

Answer 4

Strong and uniform.

Question 5

What is an electromagnet?

Answer 5

A solenoid with an added iron core
● Adding the iron core increases the
strength of the magnetic field

Question 6

What is the motor effect?

Answer 6

When a force is exerted between a
magnetic field and a current-carrying
conductor placed in that field.

Question 7

What factors affect the size of the force on a
current-carrying wire in a magnetic field?

Answer 7

The magnitude of the current flowing
through the conductor
● The strength of the magnetic field that
the conductor is placed in

Question 8

If the direction of current in a
current-carrying wire placed in a uniform
magnetic field is reversed, what happens
to the force?

Answer 8

The direction of the force is reversed.

Question 9

What criteria must be met for the equation linking
force, magnetic flux density, current and length to
hold?

Answer 9

The conductor must be at right-angles to
the magnetic field it is placed in.

Question 10

How does an electric motor work?

Answer 10

● A coil of wire, carrying a current, is placed
in a magnetic field
● The forces on the two sides perpendicular
to the field experience forces in opposite
directions
● This causes a rotational effect

Question 11

How do loudspeakers make use of the
motor effect?

Answer 11

The motor effect is used to convert
variations in the current of an electrical
circuit into the pressure variations which
produce audible sound.

Question 12

Explain how a loudspeaker works.

Answer 12

● A cone with a wire wrapped around it is connected to an
a.c power supply and is placed in a permanent
magnetic field
● When current flows through the wire, it creates a
second magnetic field, which interacts with the
permanent field
● This produces a force which causes the cone to vibrate

Question 13

How is the pitch of the sound from a loudspeaker
changed?

Answer 13

● The frequency of the a.c current is
altered
● This creates a different frequency of
vibration in the cone