Magnetism and Electromagnetism

Question 1

Define Magnetic field

Answer 1

Region where magnetic materials experience a force

Question 2

In which direction do the magnetic field lines go?

Answer 2

From north to south

Question 3

Define uniform field

Answer 3

Where the field strength (or the force experienced by an object) is the same at every point in the field.

Question 4

Practical with magnetic fields

Answer 4

Place a magnet underneath a piece of paper and scatter iron filings on top to reveal a magnetic field pattern. Tap the paper gently.
Place compass needles tip-to-tail near a magnet. Record their orientations, to plot the magnet’s field as continuous field lines.

Question 5

How can magnetism be induced?

Answer 5

If a magnetic material is brought near a magnet, it will act as a magnet. The closer they are, the stronger the induced magnetism will be.

Question 6

Does electricity create magnetism?

Answer 6

Yes. When an electric current flows through wire it will be magnetic.

Question 7

2 facts about currents in wires

Answer 7

-The larger the electric current, the stronger the magnetic field
-The direction of the magnetic field depends on the direction of the current.

Question 8

Magnetism in a straight wire

Answer 8

Concentric circles

Question 9

Magnetic field around a flat circular coil.

Answer 9

-The magnetic field in the centre is similar to a bar magnet
-Concentric ellipses of magnetic field lines around the coil.

Question 10

Magnetic field around a solenoid

Answer 10

-Strong and uniform
-Outside of the coil, the field is like the one around a bar magnet.
-The ends of a solenoid act like the north pole and south pole.
-Electromagnet.

Question 11

What makes a magnetic material soft or hard?

Answer 11

Soft- loses its induced magnetism quickly
Hard- keeps it permanently
-You can increase the strength of a magnetic field around a solenoid by adding a magnetically soft iron core through the middle of the coil.

Question 12

Define the motor effect

Answer 12

It can happen when you put a current-carrying wire in a magnetic field.

Question 13

Why does the motor effect occur?

Answer 13

When a current-carrying wire is put between magnetic poles, the two magnetic fields affect one another. The result is a force on a wire (it may move. The charged particles moving through a magnetic field will experience a force, as long as they’re not moving parallel to the filed lines.

Question 14

What happens when you reverse the direction of the current or magnetic field?

Answer 14

It reverses the direction of the force.

Question 15

In the left hand rule, what does each finger represent

Answer 15

Thumb=Direction of force
Index=Field
Middle=Current

Question 16

Define Electromagnetic induction

Answer 16

Creation of voltage in a wire which is experiencing a change in magnetic field

Question 17

Define the dynamo effect

Answer 17

Using electromagnetic induction to generate electricity using energy from kinetic energy stores.

Question 18

What are 2 ways in which you can get EM induction?

Answer 18

1. Electrical conductor moves through magnetic field.
2. Magnetic field through an electrical field changes.

Question 19

What does each part of the hand represent in the right-hand rule

Answer 19

Thumb=Direction of current
Hand= Magnetic field

Question 20

What ‘types’ of energy does the chemical energy stores in Power Stations.

Answer 20

Chemical energy store→Thermal energy store→Kinetic energy store→Kinetic energy store. Then transferred away electrically.

Question 21

Explain the process of creating electricity in power stations.

Answer 21

1. Fossil fuel burns in oxygen.
2. The energy in its chemical energy store is transferred to the thermal energy store of the water by heating.
3. Water boils and forms steam, turns the turbine, transferring energy mechanically to the kinetic energy store of the turbine.
4. Turbine revolves, so does the generator. Produces an electric current. The generator transfers energy electrically away from the station via the national grid.

Question 22

What type of current do transformers use?

Answer 22

Alternating current, so it is constant.

Question 23

Describe a transformer

Answer 23

They have two coils, the primary and the secondary, joined with an iron core.

Question 24

Describe the ratio between the voltages and the number of turns

Answer 24

The ratio between the primary and secondary voltages is the same as the ratio between the number of turns on the primary and secondary coils.

Question 25

What are step up transformers like? What do they do?

Answer 25

They increase the voltage. They have more turns on the secondary coil that the primary coil.

Question 26

What are step down transformers like? What do they do?

Answer 26

Decrease the voltage. They have more turns on the primary than the secondary.

Question 27

What’s the difference between the primary and secondary coils.

Answer 27

Primary= Connected to power source
Secondary= Induced electromagnetism.

Question 28

Transformer equation

Answer 28

V1/V2=N1/N2
(Input Prim voltage/Output sec voltage = number of turns on prim/Number of turns on sec).

Question 29

Power supply formula

Answer 29

P=IV

Question 30

Input power=Outfut power formula.

Answer 30

V1I1=V2I2

Question 31

What happens to the electricity before reaching your house?

Answer 31

A step down transformer reduce voltage so its more useful and safer.

Question 32

What is a hard magnet?

Answer 32

They get magnetised when an external magnetic field is applied and stay magnetised permanently when the external field is removed

Question 33

What is soft magnetic material?

Answer 33

They get magnetised when an external magnetic field is applied but they get demagnetised when the external field is removed

Question 34

What is the relationshin (directionwise), between current, magnetic field and force?

Answer 34

They all act perpendicular to eachother

Question 35

How do loudspeakers work?

Answer 35

-Coil inside a magnet
-AC is in the coil causes a magnetic field
-When the field interacts with the magnet, the motor effect happens
-Force pushes and pulled the wire/cone of the speaker, causing it to move in diff directions
-Due to AC, the force causes the cone to vibrate
-This causes pressure variations in the air

Question 36

How do microphones convert sound into electrical signals?

Answer 36

-When sound is produced, the pressure vibrations in the waves cause the diaphragm to vibrate
-A coil of wire is connected to the diaphragm, so as the diaphragm moves, so does the coil of the wire
-The coil of wire is in a magnet so when it moves a voltage is induced.
-As there is a complete circuit a current is also created

Question 37

How are electric motors kept rotating

Answer 37

Commutator. Switches the direction every half turn which ensures that the coil keeps spinning.

Question 38

How is electromagnetic induction used in alternators to generate alternating current?

Answer 38

A coil of wire rotates in a magnetic field. The end of this coil is connected to slip rings which will cause the current to change direction while rotating. This means ac is produced.

Question 39

What is a solenoid

Answer 39

A coil of wire which turns into an electromagnet when there is a current flowing through it

Question 40

How can you make a magnetic field in a solenoid stronger

Answer 40

-Increase current
-More turns of wire
-Use iron core

Question 41

Importance of step up transformers

Answer 41

Increase efficiency as it decreases the head loss in transmission lines. This is because for the same power, a higher voltage will lead to a lower current (P=IV). The lover the current, the less energy that is lost since P=IR