Electromagnetic Induction

Question 1

What is electromagnetic induction used for?

Answer 1

used to generate electricity

Question 2

When does electromagnetic induction happen?

Answer 2

when a voltage is induced in a conductor or a coil when it moves through a magnetic field or when a magnetic field changes through it

Question 3

What causes electromagnetic induction?

Answer 3

-by a conductor
-coil cutting through the magnetic field lines of the magnetic field

Question 4

What is the opposite of the generator effect?

Answer 4

the motor effect

Question 5

Explain the motor effect?

Answer 5

a wire already 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 6

Explain the generator effect?

Answer 6

when there is no initial current in the electrical conductor but one is induced when it moves through a magnetic field (as a result potential difference is induced across the conductor)

Question 7

How can potential difference be induced into a wire?

Answer 7

by moving the electrical conductor in a fixed magnetic field

-when a the wire is moved through a magnetic field, the wire cuts through the field lines
-this induces a potential difference in the wire

Question 8

What happens when a magnet enters a coil?

Answer 8

(the field lines cut through the turns, inducing a potential difference)

as the magnet moves through the coil, the field lines cut through the turns on the coil, inducing a potential difference in the coil

Question 9

What factors can be changed to increase induced potential difference?

Answer 9

-the speed at which the wire, coil or magnet is moved

-the number of turns on the coils in the wire

-the size of the coils

-the strength of the magnetic field

-the orientation of the poles of the magnet

Question 10

How is induced potential difference increased when increasing the speed of which the wire, coil or magnet is moved?

Answer 10

increasing the speed will increase the rate at which the magnetic field lines are cut

Question 11

How is induced potential difference increased when increasing the number of turns on the coils in the wire?

Answer 11

increasing the number of turns on the coils in the wire will increase induced potential difference because each coil will cut through the magnetic field lines and the total potential difference induced will be the result of all of the coils cutting the magnetic field lines

Question 12

How is induced potential difference increased when increasing the size of the coils?

Answer 12

increasing the area of the coils will increase potential difference induced because there will be more wire to cut through the magnetic field lines

Question 13

How is induced potential difference increased when increasing the strength of the magnetic field?

Answer 13

increasing the strength of the magnetic field will increase the potential difference induced

Question 14

How is induced potential difference increased when changing the orientation of the poles of the magnet?

Answer 14

reversing the direction in which the wire, coil or magnet is moved will increase induced potential difference

Question 15

What is the motor effect a result of?

Answer 15

two interacting magnetic fields

-one is produced around the wire due to the current flowing through it
-the second is the magnetic field into which the wire is placed, for example, between two magnets

Question 16

What happens when no current is passed through a conductor in a magnetic field?

Answer 16

it will experience no force

Question 17

What can the motor effect be used to create?

Answer 17

a simple D.C. electric motor

(the force on a current-carrying coil is used to make it rotate in a single direction)

Question 18

What is the model answer for a generator 6 marker (with a rotating coil)?

Answer 18

coil is rotated within a magnetic field

as it turns the coil cuts the magnetic field lines.

this induces a voltage (or current) in the coil.

this can then be connected to an existing circuit.

in a generator, energy is being converted from kinetic (mechanical) energy into electrical energy.

the size of the induced voltage (or current) can be increased by:

using a stronger magnet

having more turns in the coil

spinning/moving the coil faster

Question 19

What is the model answer for a generator 6 marker (with a rotating magnet)?

Answer 19

magnet is rotated within a coil

as it turns the coil cuts the constantly changing magnetic field lines from the magnet.

this induces a voltage (or current) in the coil.

this can then be connected to an existing circuit.

in a generator, energy is being converted from kinetic (mechanical) energy into electrical energy.

the size of the induced voltage (or current) can be increased by:

using a stronger magnet

having more turns in the coil

spinning/moving the magnet faster

Question 20

When the coil in a D.C. motor is horizontal are there forces acting upon it?

Answer 20

YES
current flowing through the coil produces a magnetic field (this magnetic field interacts with the uniform external field, so a force is exerted on the wire)

forces act in opposite directions on each side of the coil, causing it to rotate (using Fleming’s left-hand rule)

Question 21

When the coil in a D.C. motor is vertical are there forces acting upon it?

Answer 21

NO
no forces act on the coil when vertical, as the split ring is not in contact with the brushes

Question 22

Even through there are no forces acting on the coil in a D.C. motor when it is in a vertical position, why can the coil continue to rotate slightly?

Answer 22

even though no force acts, the momentum of the coil causes the coil to continue to rotate slightly

the split ring is used to reverse the coil’s current direction. the coil’s current must be reversed in order for it to continue rotating in the same direction. as a result, the direction of the couple rotating the coil remains the same after every half rotation, and the coil continues to rotate in the same direction.

Question 23

What factors can increase the speed at which the coil rotates?

Answer 23

-increasing the current

-increasing the strength of the magnetic field

Question 24

How can the direction of rotation of the coil in a D.C. motor be changed?

Answer 24

-reversing the direction of the current

-reversing the direction of the magnetic field by reversing the poles of the magnet

Question 25

What factors can increase the force supplied by the motor?

Answer 25

-increasing the current in the coil -increasing the strength of the magnetic field -adding more turns to the coil

Question 26

What kind of current passes through the coil of the loudspeaker and what does it create?

Answer 26

an alternating current that creates a changing magnetic field around the coil

Question 27

How are the sound waves created in a loudspeaker?

Answer 27

as the magnetic field is constantly changing direction (due to the alternating current), the force exerted on the coil will constantly change direction which will make the coil oscillate the oscillating coil causes the speaker cone to oscillate this makes the air oscillate, creating sound waves

Question 28

What is a transformer?

Answer 28

a device used to change the value of an alternating potential difference or current (it is achieved using the generator effect)

Question 29

What does a basic transformer consist of?

Answer 29

-a primary coil -a secondary coil -an iron core

Question 30

Why is an IRON core used in a transformer?

Answer 30

iron is used because it is easily magnetised

Question 31

How does a transformer work?

Answer 31

an alternating current is supplied to the primary coil the current is continually changing direction (this means it will produces a changing magnetic field around the primary coil) the iron core is easily magnetised, so the changing magnetic field passes through it as a result there is now a changing magnetic field inside the secondary coil, this changing field cuts through the secondary coil and induced a potential difference as the magnetic field is continually changing the potential difference induced will be alternating if the secondary coil is part of a complete circuit it will cause an alternating current to flow

Question 32

Can a transformer change the size of an alternating voltage?

Answer 32

YES

Question 33

What 3 other roles does a transformer have?

Answer 33

1) to increase the potential difference of electricity before it is transmitted across the national grid 2) to lower the high voltage electricity used in power lines to the lower voltages using in houses 3) used in adapters to lower mains voltage to the lower voltages used by many electronic devices

Question 34

What is a step-up transformer and how does it work?

Answer 34

a step-up transformer increases the potential difference of a power source, it has more turns on the secondary coil than on the primary coil

Question 35

What is a step-down transformer and how does it work?

Answer 35

a step-down transformer decreases the potential difference of a power source, it has fewer turns on the secondary coil than on the primary coil

Question 36

What does a step-up transformer do in electricity transmission?

Answer 36

-when electricity is transmitted over large distances, the current in the wires heats them, resulting in energy loss -the electrical energy is transferred at high voltages from power stations -it is then transferred at lower voltages in each locality for domestic uses the voltage must be stepped up by a STEP-UP transformer-these are places after the power station

Question 37

What does a step-down transformer do in electricity transmission?

Answer 37

for domestic use of electricity, the voltage must be much lower this is done by stepping down by the voltage using a STEP-DOWN transformer-these are places before buildings

Question 38

What is the equation that shows the relationship between input (primary) and output (secondary) voltages and the turns ratio for a transformer?

Answer 38

input (primary) voltage / output (secondary voltage = primary turns / secondary turns

Question 39

What factors does the output potential difference depend on?

Answer 39

-the number of turns on the primary and secondary coils -the input potential difference (voltage)

Question 40

What is input power equal to?

Answer 40

input power = output power (for 100% efficiency)