P7 - Electromagnetic effects (to be continued)

Question 1

An electromotive force (e.m.f) is needed for a

Answer 1

current to flow

Question 2

What are the two ways to increase the magnitude of an induced e.m.f

Answer 2

1. increase the field strength

2. Increase the speed at which the wire is moved

Question 3

What is the motor effect

Answer 3

when a wire carrying an electric current passes through a magnetic field perpendicularly and experiences a force for both the field and wire

Question 4

What does the size of the force depend on in the motor effect

Answer 4

The magnitude of the current and strength of the field

Question 5

What is the use of Fleming’s left hand rule

Answer 5

it predicts the direction of the force

Question 6

What does the thumb represent in Fleming’s left hand rule

Answer 6

force

Question 7

what does the index finger in Fleming’s left hand rule

Answer 7

field

Question 8

what does the third finger in Fleming’s left hand rule

Answer 8

current

Question 9

An electric motor transfers electrical energy to

Answer 9

kinetic energy

Question 10

What is an electric motor made from

Answer 10

a coil of wire positioned between the poles of two permanent magnets

Question 11

In an electric motor what happens

Answer 11

The current passing through the wire creates a magnetic field which interacts with the magnetic field produced by the two magnets exerting a force on the sides of the coil

Question 12

What is the job of a split ring commutator in a d.c motor

Answer 12

ensure that a motor continues to spin by reversing the direction of the current so the forces on the coil are reversed and continue rotating

Question 13

In a d.c motor what does the motor coil experience

Answer 13

one side feels a force upwards and the other side feels a force downward creating a spin

Question 14

Without a commutator what would happen to the motor

Answer 14

It would rotate 90 degrees and then just stop making it useless

Question 15

3 ways to make the motor spin faster

Answer 15

Increase the current
Increase the strength of the magnetic field
Increase number of turns of wire in the coil

Question 16

If you change the direction of current or reverse magnetic field what direction does the motor spin in

Answer 16

the opposite direction

Question 17

An e.m.f is induced in a wire in a complete circuit when

Answer 17

The wire is moved through a magnetic field
or
Magnetic field is moved past the wire
or
Magnetic field around the wire changes strength

Question 18

A direct current (d.c) is produced when

Answer 18

a steady current is produced by a battery that passes from the negative to positive terminal of the battery

Question 19

In a (d.c)

Answer 19

voltage stays constant throughout the circuit

Question 20

What is current where the electrons in a circuit move back and forth

Answer 20

alternating current (a.c)

Question 21

Electricity generated at power stations is

Answer 21

a.c

Question 22

What is a dynamo

Answer 22

a simple current generator

Question 23

Turning the permanent magnet inside a coil

Answer 23

reverses its magnetic field every time the magnet is rotated 180 degrees

Question 24

The dynamo induces a

Answer 24

alternating current in the wires of the coil.

Question 25

Power stations use rotating electromagnets instead of

Answer 25

permanent magnets to create a magnetic field

Question 26

The frequency in a dynamo depends on

Answer 26

how fast it’s spinning

Question 27

What does a transformer consist of

Answer 27

two coils of insulated wire on a piece of iron

Question 28

When alternating voltage is applied to the first (primary) coil it produces a

Answer 28

changing magnetic field in the core which induces an alternating e.m.f in the secondary coil

Question 29

Why is the strength of a magnetic field increased in the transformer

Answer 29

because the iron is soft and easily magnetized

Question 30

What happens when there are more turns on the secondary coil than the primary coil

Answer 30

the voltage across the secondary coil will be greater than the voltage across the primary coil

Question 31

What is the term for when a secondary coil has more turns than the primary coil

Answer 31

step up transformer

Question 32

A transformer with fewer turns on the secondary coil than the primary coil is called

Answer 32

a step down transformer

Question 33

The voltage and turns are _________ in a transformer

Answer 33

proportional

Question 34

If the primary coil has 100 turns and input is 12V and the secondary coil has 500 turns how many V is the output

Answer 34

6V

Question 35

If the primary coil has 1000 turns and input is 12V and the secondary coil has 4000 turns how many volts does it produce

Answer 35

48V

Question 36

Formula for turns and voltage in transformer

Answer 36

primary coil voltage/secondary coil voltage = number of primary turns/number of secondary turns