Electricity & Magnetism

Question 1

Define Electricity

Answer 1

A form of energy associated with stationary or moving electrons or other charged particles

Question 2

Electric charges exert …

Answer 2

forces on one another

Question 3

Like charges…

Answer 3

repel

Question 4

Opposite charges…

Answer 4

attract

Question 5

The magnitude if the force between the charges depends upon…

Answer 5

the medium in which they lie and its maximum in a vacuum

Question 6

The magnitude of force is inversely proportional to…

Answer 6

the distance between the charges, the smaller the distance, the greater the force

Question 7

Coulomb’s Law

Answer 7

F is inversely proportional to q1xq2 / d2
F = force (newtons)
q1 and q2 = 2 charges (coulombs)
d = distance apart (metres)

Question 8

Describe a photon and give an example

Answer 8

a small bundle of energy with no charge and no mass, x-rays and gamma rays are photons

Question 9

Describe charge

Answer 9

measured in coulombs, a single charge can exist in isolation, 1 coulomb is the charge carried by 6.25 x 10 to the power 18 electrons

Question 10

1 coulomb is …

Answer 10

the amount of charge that flows during 1 second if there is a current of 1 ampere

Question 11

Define Field and give an example

Answer 11

A field is any region in space where a particular entity exerts its influence - e.g. electric, magnetic, gravitational
(Always remember fields are 3D)

Question 12

The direction the lines point in an electric charge diagram show …

Answer 12

the direction in which an isolated POSITIVE charge would move if placed at any point in the field

Question 13

The strength of a field is indicated by…

Answer 13

how close the lines are together

Question 14

When an electric field is associated with 2 parallel plates, the direction of the electric field is …

Answer 14

postive to negative

Question 15

A postive electrode is called …

Answer 15

anode

Question 16

A negative electrode is called …

Answer 16

cathode

Question 17

When does an electron move

Answer 17

when there is a difference in the electrical potential or ‘potential difference’ (p.d.)

Question 18

What is the unit of p.d.

Answer 18

volts (V)

Question 19

Why can we measure energy in electronvolts (eV)

Answer 19

because an electron moves when placed in an electric field - as it moves it gains kinetic energy, the higher the voltage, the more kinetic energy it gains

Question 20

Describe the electronvolt (eV)

Answer 20

This is the amount of energy gained by an electron when it moves through a p.d. of 1 volt

Question 21

Describe an electric current

Answer 21

whenever a charged particle moves (A)

Question 22

Material through which a current flows is called a …

Answer 22

conductor

Question 23

Electric currents can flow through

Answer 23

solid, gases and vacuums

Question 24

To have a circuits there must be …

Answer 24

a potential difference and no gaps

Question 25

How are Voltage, Current and Resistance in a circuit related?

Answer 25

By Ohm's Law

Question 26

Describe Ohm's Law

Answer 26

``` The current (I) flowing through a metallic conductor is proportional to the potential difference (V) across it, provided that all its physical conditions (e.g. its temperature) remains constant I is proportional V ```

Question 27

Describe resistance

Answer 27

the opposition a material presents to a flow of electrons - measured in ohms

Question 28

Describe an insulator

Answer 28

a material whose electrical resistance is so high that current cannot normally flow through it (e.g. rubber, plastic, wood)

Question 29

The resistance of a conductor can be introduced to Ohm's Law and rewritten ...

Answer 29

I = V/R

Question 30

Definition of the Ohm

Answer 30

A conductor is said to have an electrical resistance of 1 ohm if a potential difference of 1 volt across it produces an electrical current of 1 ampere through it

Question 31

Transformers

Answer 31

increase or decrease voltage

Question 32

There are 2 types of magnetic pole ...

Answer 32

north & south, like poles = repel, opposite poles = attract

Question 33

Main/Only difference between electricity and magnetism

Answer 33

A single magnetic pole cannot exist in isolation but a single charge can exist in isolation

Question 34

Magnetic Flux Density

Answer 34

the number of lines in a given area of space, measured in Tesla

Question 35

A magnetic field is only present when ...

Answer 35

the current is on

Question 36

Formula to find the force between two magnetic poles

Answer 36

F is proportional to m1 x m2 / d2

Question 37

The lines of force are ...

Answer 37

circular and concentric with the long axis of the wire

Question 38

The direction of the field depends on ..

Answer 38

the direction of the current

Question 39

Name the 3 factors affecting the strength of the magnetic field in a current-carrying solenoid

Answer 39

The number of turns - as number increases, the number of lines of magnetic flux increase in proportion Current - as it increases through the coiled wire, the magnetic field strength increases up to a maximum presence of ferromagnetic (soft iron) core - inserting a care through the centre of the wire greatly increases the magnetic field

Question 40

If a current is flowing through a resistance (e.g. wire) it causes ...

Answer 40

heat to be generated and therefore wastes energy

Question 41

Most MRI systems use ... explain ...

Answer 41

a superconducting magnet - consists of many coils of wire through which an electric current is passed creating a magnetic field of up to 2.0 Tesla

Question 42

Maintaining such a large magnetic field consumes energy, explain how this is minimised ...

Answer 42

minimised by reducing the resistance in the wire to almost zero by continually bathing them in liquid helium 269.1 below zero Celsius - insulated by a vacuum

Question 43

A strong magnetic field allows for ... and superconductivity allows for ...

Answer 43

high quality images, the system to operate economically