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 is a solenoid?

Answer 2

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

Question 2

describe the magnetic field found inside a solenoid.

Answer 2

strong and uniform.

Question 3

when using Fleming’s left hand rule what does the forefinger represent?

Answer 3

the forefinger points in the direction of the magnetic field.

Question 4

what is the motor effect?`

Answer 4

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

Question 4

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

Answer 4

• the magnitude of the current flowing through the wire
• the distance from the wire

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 5

what rule is used to determine the force experienced due to the motor effect?

Answer 5

Fleming’s left-hand rule

Question 5

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

Answer 5

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

Question 5

when using Fleming’s left hand rule what does the second finger represent?

Answer 5

the second finger points in the direction of current flow in the conductor.

Question 5

if the strength of the current in a current-carying wire placed in a uniform magnetic field is increased, what happens to the force?

Answer 5

the strength of the force is increased.

Question 6

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

Answer 6

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

Question 7

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

Answer 7

the direction of the force is reversed.

Question 8

what is the unit used for magnetic flux density?

Answer 8

tesla, T

Question 8

how do loudspeakers make use of the motor effect?

Answer 8

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

Question 8

how does an electric motor work?

Answer 8

• 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 8

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

Answer 8

• the frequency of the a.c current is altered
• this created a different frequency of vibration in the cone

Question 9

explain how a loudspeaker works.

Answer 9

• 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