Electromagnetism

Question 1

What 2 things happens when an electric current flows through a wire?

Answer 1

Heats up

Creates a magnetic field

Question 2

Give 3 rules of electromagnetic fields caused by wires?

Answer 2

As current increases, magnetic field gets stronger
Magnetic field gets weaker further away from wire
Direction of lines can be found using compass

Question 3

Give 2 rules about magnetic fields created by coils?

Answer 3

In a coil, the magnetic field can be made stronger by increasing the current
The magnetic field can be made stronger by increasing the number of turns in a coil

Question 4

What is a solenoid?

Answer 4

A wire that is wrapped in to a coil, and has current passed through it creating a magnetic field

Question 5

Give 3 ways the strength of a magnetic field created by a solenoid can be increased?

Answer 5

Using larger current
Using more turns in wire
Putting soft iron rod in to middle of solenoid

Question 6

What does putting a soft iron rod in to the middle of a solenoid turn the coil in to?

Answer 6

A simple electromagnet

Question 7

Give advantages of electromagnets over magnets?

Answer 7

Strength of an electromagnet can be varied

The electromagnet can be switched off

Question 8

Why is steel not a suitable core for an electromagnet? And why is a soft iron rod better?

Answer 8

Steel would be permanently magnetised after current passed through the coil. Soft iron is easily magnetised and demagnetised

Question 9

Give 2 uses of electromagnets?

Answer 9

Separate metals from non metallic materials

To lift magnetic materials in scrapyards

Question 10

What is the motor effect when a magnetic force acts on a current carrying wire?

Answer 10

A copper wire placed between 2 magnets of opposite poles has no force acting upon it as it is not magnetic. But when current passes through, a force is acted upon the wire

Question 11

Explain the motor effect?

Answer 11

When current passes through the non magnetic wire, it creates its own magnetic field, which distorts the magnetic field of the 2 magnets. The distorted magnetic field usually then straightens, pushing against the magnetic field around the wire, and causing the wire to move

Question 12

How can the direction of the wire in the motor effect be predicted?

Answer 12

Flemings left hand rule

Question 13

In Flemings left hand rule, what does the;
Thumb represent
Index finger represent
Middle finger represent?

Answer 13

Thumb is motion of wire
Index is magnetic field of magnets
Middle is current in wire

Question 14

Give 3 ways force of motor effect can be increased?

Answer 14

Current in wire increased
Stronger magnets
Length of wire exposed to magnetic field increased

Question 15

What direction to magnetic field lines go?

Answer 15

From north to south

Question 16

What direction does current flow in a circuit?

Answer 16

From the positive to the negative

Question 17

What is the turning effect?

Answer 17

Basically the motor effect, but with a loop of wire between the 2 magnets. Opposite directions of current on either side of the loop cause one side of the loop to go up, and the other to go down, causing the loop to turn

Question 18

Give 3 ways the turning effect can be increased?

Answer 18

Increasing the number of turns in the loop, to form a coil
Increasing current in loop
Increasing area of loop

Question 19

Give 1 application of the turning effect?

Answer 19

The d.c. Electric motor

Question 20

What is d.c.?

Answer 20

Direct current

Question 21

What is electromagnetic induction?

Answer 21

When a conductor moves through a magnetic field, producing current

Question 22

Give 4 factors that affect the current produced through electromagnetic induction?

Answer 22

Direction of movement
Speed of movement
Magnet strength
Creating loops of a conductor to make a coil

Question 23

Explain how direction of movement can affect electromagnetic induction?

Answer 23

The conductor must cross the magnetic field lines, and so moving it vertically produces current, but laterally will not

Question 24

Apart from moving a conductor through a magnetic field, how else can electromagnetic induction be caused?

Answer 24

By keeping the conductor stationary and moving the magnetic field

Question 25

Why is current produced through electromagnetic induction?

Answer 25

The work done/ energy used when moving the conductor or the magnetic field, creates current.

Question 26

Give an application of electromagnetic induction?

Answer 26

The a.c. generator, AKA the alternator

Question 27

What are magnets?

Answer 27

These are materials which attract magnetic substances, such as iron, which is ferromagnetic

Question 28

How is electricity generally generated and transmitted?

Answer 28

It's generated at power stations, which use generators. This electricity is then fed to a huge step - up transformer which transfers power to overhead cables at a greatly increased voltage. These cables feed power to the grid, which is then distributed to substations. These contain step - down transformers which reduce the voltage. This power is then fed in to the homes

Question 29

Why are step up transformers used to increase the voltage of the electricity generated in power stations?

Answer 29

They are used to reduce the current flowing in the cables, so as to waste less energy. This is because when current flows through a conductor ( the cables ) some energy is lost due to resistance

Question 30

Describe the number of primary and secondary coils in a step up transformer? Why is this?

Answer 30

Primary coil has very few turns, but secondary coil has many turns. This is because of the transformer equation. So the more turns on the secondary coil than on the primary coil, the higher the voltage will have to be

Question 31

Describe the number of turns in the primary and secondary coils in a step down transformer?

Answer 31

Primary has many turns, secondary has few turns

Question 32

What core is often used in transformers? How does it work?

Answer 32

Laminated iron core, connects the coils magnetically

Question 33

Why does current get lower as the voltage increases?

Answer 33

This is due to the law of conservation of energy, so the power entering the transformer, must equal the power leaving it

Question 34

Give the transformer equation?

Answer 34

V(Primary) V ( Secondary ) ------------------------- = ------------------------ No. Turns in coil (Primary) No. Turns in coil ( secondary )

Question 35

How do transformers work?

Answer 35

Alternating current in primary coil converts coil in to electromagnet, which produces an alternating magnetic field. Core transports alternating field to secondary coil. Secondary coil is a conductor in changing magnetic field, so electricity is produced through electromagnetic induction.

Question 36

What is the electromagnetic induction in transformers also known as?

Answer 36

Mutual induction

Question 37

What type of current is the only current transformers work with?

Answer 37

a.c. Alternating current

Question 38

Why do transformers not work with direct current?

Answer 38

No alternating current in primary coil, means no alternating magnetic field. This means no electromagnetic induction, and therefore no output voltage in secondary coil

Question 39

Give 2 equations to calculate how much electrical power is lost due to the heating effect in resistors?

Answer 39

``` Power = Current2 X Resistance P = I2 X R ``` Power = Voltage2 -------- Resistance P = V2 --- R