Electricity and magnetism

Question 1

How do you work out power?

Answer 1

Power=current X voltage

Question 2

How do you work out I?

Answer 2

I means current

Current = power/voltage

Question 3

What is the units for charge

Answer 3

Coulombs C

Question 4

How to work out resistance?

Answer 4

Resistance= voltage/current

Question 5

What is the units for resistance?

Answer 5

Ohms

Question 6

How do you work out energy in circuits?

Answer 6

Energy= power X time (s)

Question 7

What is current measured in?

Answer 7

Amps

Question 8

What is a fuse and why is it important?

Answer 8

A fuse is a thin piece of wire which is designed to melt if the current flows for it is too high

A fault in a circuit might cause a large current

This may damage the device or start a fire

A fuse is to prevent this from happening

Question 9

What is a magnet

Answer 9

Magnets have a magnetic field that exert a force onto another body that has magnetic properties

Question 10

What are the types of magnets

Answer 10

Permanent magnet- always has a magnetic field

Temporary magnet- becomes magnetic under domain influence. Under influence of another magnet

Question 11

What are the types of magnetic material?

Answer 11

Ferromagnetic- e.g iron, retains magnetism

Paramagnetic- e.g copper, low permeability
Gadolinium is used in MRI to improve images

Dramagnetic- No magnetism

Question 12

What is domain theory?

Answer 12

Domains are areas in the magnet that align in order for the substance to be magnetic

So in substances that don’t have domains aligned they aren’t magnetic
-however some substances can have their domains with other magnets.

Question 13

What affects the magnitude of force?

Answer 13

Propertional- strength of the magnets

Inversely proportional to the distance squared (the further away the weaker the force)

Question 14

What are the units of magnetic field strength or magnetic flux density?

Answer 14

Measured in Gauss (G) (Not SI units)

Or Tesla (T) (SI units)

Question 15

How many Gauss’s equal 1 Tesla

Answer 15

1 Tesla= 10,000 Gauss

Question 16

How can magnetic fields arise?

Answer 16

Magnetic fields can arise due to current carrying conductors

As electrons flow a magnetic field will be generated around a electric wire

Question 17

What is Lenz’s law?

And what can it cause?

Answer 17

The induced EMF is in the opposite direction to what caused it

This leads to power loses as the current generated is inhibited by the magnetic field as it opposes it

Question 18

What does EMF stand for?

Answer 18

EMF- electromotive force is similar to potential difference

Question 19

What are the principals of magnetive?

Answer 19

Generator effect

Motor effect

Question 20

What are the electromagnetic laws?

Answer 20

Faraday’s laws

Question 21

What is the generator effect?

Answer 21

…..

Similar to motor effect execpt in reverse

Question 22

What is the motor effect?

Example

Answer 22

Coil of wire placed in a magnetic field, so when the current flows it creates a MF that opposes the first MF, which causes the coil to rotate. The rotation/movement can drive devices.

For Example, an induction motor spins the anode on the x-ray tube.

Question 23

What are the Faraday’s laws?

Answer 23

….

Question 24

What the influence of sharp objects on electric field?

And how to prevent it?

Answer 24

Charge collect around the surface of a object and sharp edges will have a higher concentration of charge.
This can result in electrical shock

To prevent this -earth them, no sharp edges

Question 25

What does current mean?

Answer 25

The number of electrons

Question 26

What's another word for voltage?

Answer 26

Potential difference

Question 27

What does resistance mean and factors that effect it?

Answer 27

Resistance means that electrons are prevented from flowing Heat increases resistance Thin wires have more resistance And thick wires have less resistance as electrons can flow more easily and heat up less quickly

Question 28

What does potential difference mean?

Answer 28

``` Potential difference (voltage) is the driving force, However current is the flow of electrons so in none circuits there is potential difference ``` But in circuits there is a flow of electrons

Question 29

What measure of current would you use in rad?

Answer 29

In rad milliamps (1mA=0.001Amp

Question 30

What is a semi- conductor

Answer 30

Semi-conductors permit the flow of electrons in one direction only (used to regulate flow in a circuit) e.g silicon

Question 31

What's the units for power?

Answer 31

Watts

Question 32

What's the units for energy?

Answer 32

Joules

Question 33

What is a solenoid?

Answer 33

Solenoid refers to a soft iron being used in the coil to strengthen the magnetic field Current creates a magnetic field in the wire and the soft iron enhances it

Question 34

Why is electricity needed in an x-ray tube?

Answer 34

To cause electrons to be released from the cathode To drive electrons to the anode for photon production

Question 35

What are the types of electrical current?

Answer 35

``` Direct current (D.C) Alternating current (A.C) ```

Question 36

What does direct current mean?

Answer 36

Flows in one direction does not change in direction when it reaches its peak

Question 37

What does alternating current mean?

Answer 37

Changes in direction but it reaches it's peak

Question 38

What does Faraday's law of electromagnetic induction mean?

Answer 38

When a conductor is placed in an changing magnetic field EMF is induced and if the conductor circuit is closed current is also induced. Changing magnetic field induces alternating current.

Question 39

What device is used to get direct current from alternating current

Answer 39

Commutator (split ring) is used

Question 40

How does a step-up transformer work

Answer 40

If there is more coils in the secondary coil than the primary coil it steps up the voltage.

Question 41

How does a step-down transformer work?

Answer 41

If there is less coils in the secondary coil than the primary coil it steps down the voltage.

Question 42

What does a rectifier do?

Answer 42

Converts alternating current to direct current.

Question 43

How does a transformer work

Answer 43

It steps up or step downs the voltages The changing magnetic field induces in the secondary coil This is mutual induction