Electricity

Question 1

Current

Answer 1

Flow of electric charge round a circuit
Unit: ampere A

Size of current is rate of flow of charge

Question 2

Potential difference

Answer 2

The driving force that pushes the current around
Unit: volt V

Energy transferred per unit charge

Question 3

Resistance

Answer 3

Anything which slows the current down

Unit: ohm

Question 4

Which direction does conventional current flow

Answer 4

Positive to negative

Question 5

Charge (Q)

Answer 5

Coulombs C

Question 6

Ammeter

Answer 6

Placed in series

Question 7

Voltmeter

Answer 7

Placed in parallel around the component being measured (not battery or variable resistor)

Question 8

Resistors IV graph

Answer 8

Current is directly proportional to the voltage

Question 9

Filament lamp IV graph

Answer 9

Like an x2 curve as temp increases so does resistance

Question 10

Diode IV graph

Answer 10

Current only flows in one direction so current is 0 in x < 0

Question 11

Why does resistance increase with temp

Answer 11

Ions are vibrating more as they have more energy

This makes it more difficult for the electrons to flow through as they are moving more and ‘getting in the way’

Question 12

Why are LED useful

Answer 12

Used as lighting as they use less current than most forms

They indicate presence of a current so can be used to show devices are switched on

Question 13

Use of diodes

Answer 13

Can rectify ac surrender through half wave recirfication to turn it into dc

Question 14

Uses of LDRs

Answer 14

In bright light resistance falls
In low light resistance increases
Used in automatic night lights (become bright when it is dark)
Used in burglar detectors
(If burglar breaks a beam of light resistance shoots up and turns on bright light)

Question 15

Resistance in thermistors

Answer 15

Decreases in hot temp
Increases in low temp
Used as temperature sensors and thermostats

Question 16

In a series circuit

Answer 16

PD is shared i.e. PDs add together to make the source voltage

Current is the same everywhere

Resistance adds up to make total resistance (larger the resistance of each component the more PD is takes up)

Cell voltages add up to make total

Question 17

Parallel circuits

Answer 17

PD is the same across all components

Current is shared between branches

Question 18

Mains supply

Answer 18

AC current or 230V

Frequency is 50Hz

Question 19

Oscilloscope traces

Answer 19

In DC voltage is always the same so it is a straight line

In AC it is always changing so the line is wavy (vertical height at any point shows voltage then)

Question 20

Frequency =

Answer 20

1/time period

Question 21

Brown wire

Answer 21

Live wire which alternates between high positive and low negative voltage

Question 22

Blue wire

Answer 22

Neutral wire stays at 0V

Question 23

Green and yellow wire

Answer 23

Earth wire is for safety and is attached to metal casing of appliance and carries electricity to the earth if the live or neutral wires touch the metal casing

Question 24

features of 3 pin plug

Answer 24

Plastic casing of plug
Wires covered in plastic
Order is blue yellow and green brown
Thicker cables have less resistance
Brass and copper and good conductors so used for pins

Question 25

Advantages of circuit breakers

Answer 25

Can be reused
Faster
Work for even small current changes
But expensive

Question 26

RCCB

Answer 26

Normally same current flows through live and neutral wires
If someone touches the live wire a current flows through them meaning neutral wire carries less current than live wire
RCCB detects this difference and cuts off a switch

Question 27

National grid

Answer 27

In order to transfer large amounts of electricity (power) current or voltage must be v high

High current loses lists of energy through heating wires so voltage is increased to
400,000 V using a transformer
Step down transformers in towns take it down to a safe level of 230V