Electricity

Question 1

What does a simple electrical circuit require?

Answer 1

• a conductor for current to flow
• a source of potential difference

Question 2

What is the definition of electric current?

Answer 2

The rate of flow of electric charge

Question 3

What is the unit for current?

Answer 3

Amperes or amps

Question 4

What is 1 amp equivalent to?

Answer 4

1 coulomb per second

Question 5

What is the equation to find current?

Answer 5

I=Q/t

Question 6

When does current flow?

Answer 6

When a conductor such as a wire connects two oppositely charged terminals

Question 7

In Electric circuits, what is the current a flow of?

Answer 7

Electrons

Question 8

Which direction do electrons flow?

Answer 8

Negative to positive

Question 9

How is current measured?

Answer 9

Using an ammeter

Question 10

How must an ammeter be connected in a circuit?

Answer 10

In series with the component that is being measured?

Question 11

What is the definition of potential difference?

Answer 11

The electrical work done per unit charge flowing between two points

Question 12

What is p.d. Measured in?

Answer 12

Volts

Question 13

What is 1 volt equivalent to?

Answer 13

The transfer of 1 joule of electrical energy by 1 column of charge, 1 joule/coulomb

Question 14

What is the equation that describes potential difference?

Answer 14

V=W/Q

Question 15

How does a simple cell create a potential difference?

Answer 15

Through separation of charge:
- one terminal positive charge other is negative
- electrons repelled by -ve terminal and attract to +ve terminal
- the potential difference causes a flow of electrons

Question 16

What happens to the energy of an electron as they flow through a cell vs through a circuit?

Answer 16

Cell: gain energy
Circuit: lose

Question 17

How can p.d be measured?

Answer 17

Voltmeter

Question 18

How must a voltmeter be set up?

Answer 18

In parallel to the component

Question 19

What is the definition of resistance?

Answer 19

The opposition of a component to the flow of electric current through it.
The ratio of potential difference in a conductor to the current in it

Question 20

What is resistance measured in

Answer 20

Ohms

Question 21

What is the equation to describe resistance?

Answer 21

R=V/I

Question 22

What does the resistance of a component control the size of?

Answer 22

The current in a circuit

Question 23

For a given p.d, if you increase resistance what happens to the current?

Answer 23

It decreases

Question 24

Why are copper wires known to be good conductors?

Answer 24

The have low electrical resistance

Question 25

What is ohm’s law?

Answer 25

For a conductor at a constant temperature, the current through it is proportional to the potential difference across it

Question 26

What does constant temperature in ohms law suggest about resistance?

Answer 26

Resistance is constant

Question 27

What is the equation that represents ohms law?

Answer 27

V=IR

Question 28

How can you calculate resistance using an IV graph that investigates ohms law?

Answer 28

1/gradient

Question 29

What does An I-V graph show?

Answer 29

The relationship between current and voltage for different components

Question 30

For an ohmic conductor, what does the I-V graph look like?

Answer 30

A straight line through the origin

Question 31

For a semiconductor diode what is the I-V graph shape?

Answer 31

A horizontal line that sharply inclines

Question 32

For a filament lamp what is the shape of the I-V graph?

Answer 32

Has an ‘S’ shape

Question 33

What is forward bias in a semiconductor diode? And how is this shown by the graph?

Answer 33

When the current is in the direction of the arrowhead symbol of the diode. It is shown on the graph as the re is a sharp increase in p.d and current

Question 34

What is reverse bias in a diode and how is this shown on an I-V graph?

Answer 34

When diode is switched around and doesn’t conduct. Graph reads zero in the negative x quadrant

Question 35

Why does current in a filament lamp increase at a proportionally slower rate?

Answer 35

The resistance in the filament increases as the temperature increases due to more current

Question 36

Why do all materials have some resistance to the flow of charge?

Answer 36

The electrons collide with metal ions in a wire, they transfer kinetic energy and causes electrical heating. This resists the flow of charge

Question 37

What does resistance depend on?

Answer 37

The length of the wire The cross sectional area The resistivity of the material

Question 38

What is the equation of resistance?

Answer 38

R=(Length x resistivity)/cross sectional area

Question 39

If you increase the length of the wire what happens to the resistance

Answer 39

Increases

Question 40

If you increase the thickness of the wire what happens to the resistance?

Answer 40

Smaller resistance

Question 41

What is the definition of resistivity

Answer 41

The extent to which a material opposes the flow of electric current through it

Question 42

What is resistivity dependent on?

Answer 42

The temperature

Question 43

What happens to the resistance in a thermistor if the temperature increases?

Answer 43

Decreases

Question 44

Are thermistors ohmic conductors?

Answer 44

No

Question 45

What are the applications of a thermistor?

Answer 45

Fire alarms, circuits in ovens and digital thermometers

Question 46

How is a superconductor created?

Answer 46

A material is cooled below the critical temperature and there is no resistivity?

Question 47

What is the definition of a superconductor

Answer 47

A material with no resistance below a critical temperature

Question 48

Give 1 example of a common superconducting material

Answer 48

Mercury

Question 49

In which situations are superconductors useful?

Answer 49

When a large current is required: - produce strong magnetic fields - reduce energy loss E.g. MRI scanners, motors, maglev trains, fusion reactors

Question 51

What is the combined resistance in a series circuit equal to?

Answer 51

The sum of the individual resistances

Question 53

What is the reciprocal of the combined resistance of a parallel circuit equal to?

Answer 53

The sum of the reciprocals of the individual resistances

Question 54

In a parallel circuit, if you add more resistors, what happens to the combined resistance?

Answer 54

It is lower