2 Electricity

Question 1

Double Insulation

Answer 1

Class 2 appliances have metal cases
Plastic is an insulator so no earth wire
Example: hairdryer

Question 2

Fuses and Circuit Breakers

Answer 2

1. Fault occurs (live wire touches metal case)
2. Large current flows down to earth wire and melts fuse
3. Fuse breaks, disconnecting the live supply

Question 3

Current

Answer 3

The rate of flow of charge

Question 4

What is the conventional current?

Answer 4

• Opposite of ACTUAL current
• Goes from + to -

Question 5

Voltage

Answer 5

energy lost or gained by each Coulomb as it moves around the circuit

Question 6

Kirchoff’s Law

Answer 6

Total current entering a junction = Total current leaving a junction

Question 7

Different types of circuit

Answer 7

• Series
• Parallel

Question 8

Series Circuit

Answer 8

Current is the same throughout
Voltage is shared between components

Single Loop

Question 9

Parallel Circuit

Answer 9

Share of current for each loop
Voltage is same throughout (for each loop)

Multiple Loops

Question 10

Advantages of Parallel Circuit

Answer 10

If one component fails, other components are unaffected
Individual control over each component or loop/components work independently

Question 11

Disadvantages of Series Circuit

Answer 11

If one component fails, whole circuit is disconnected

Question 12

Resistance

Answer 12

Opposition to the flow of charge due to collisions between electrons (moving) and nuclei (stationary)

Question 13

How can the resistance of a conductor be increased?

Answer 13

• Reduce cross-sectional area
• Increase length

Question 14

What can be used to indicate the presence of a current in a circuit?

Answer 14

Lamp or LED

Question 15

Relationship with voltage and current in a resistor(Ohms Law)

Answer 15

The current is directly proportional to the voltage, provided that the temperature is constant

Question 16

Relationship between voltage and current in a filament lamp

Answer 16

As voltage + current increase, so does resistance.
Due to nuclei vibrating more making it more difficult for electrons to pass through.

Question 17

Diode

Answer 17

Electrical equivalent of a 1 way valve (only lets current flow in 1 direction)

Question 18

Graph for Diode (Voltage and current)

Answer 18

Peaks as soon as voltage is positive

Question 19

LDR graph (brightness and resistance)

Answer 19

Inversely proportional

Question 20

Uses of LDR

Answer 20

Screen brightness on electronic devices

Question 21

Thermistor graph (temperature and resistance)

Answer 21

Inversely proportional

Question 22

Alternating Current (a.c)

Answer 22

Voltage continuously changes from + to -

Question 23

Example of alternating current

Answer 23

Mains electricity

Question 24

Direct Current (d.c)

Answer 24

Voltage is always positive

Question 25

Example of Direct Current

Answer 25

Cell

Question 26

Wires in a plug

Answer 26

* Live * Neutral * Earth

Question 27

Colours of wires in plug: Live

Answer 27

Brown

Question 28

Colours of wires in plug: Neutral

Answer 28

Blue

Question 29

Colours of wires in plug: Earth

Answer 29

Green/yellow

Question 30

Plugs: Live

Answer 30

Alternates between + and - voltages, as electrons are pushed around the circuit

Question 31

Plugs: Neutral

Answer 31

Stays at 0V, but carries same current as live

Question 32

Plugs: Earth

Answer 32

Stays at 0V, and doesn't carry a current unless there is a fault

Question 33

Examples of electrical hazards

Answer 33

Frayed cables Water around plugs Damaged plugs

Question 34

Voltage of Mains electricity

Answer 34

230V

Question 35

Practical: investigate how insulating materials can be charged by friction

Answer 35

Rub duster on polythene rod Polythene rod becomes positive Duster becomes negative Due to transfer of electrons

Question 36

Uses of electrostatic charges

Answer 36

* Photocopiers * Inkjet printers

Question 37

Uses of electrostatic charges: Photocopiers

Answer 37

1. A copying plate is electrically charges 2. An image of the page wanting to be copied is projected on the plate 3. Where light falls on the plate, electrical charge leaks away 4. The parts charges attract a black powder 5. The powder is transferred to paper 6. Paper is heated to make powder stick

Question 38

Dangers of electrostatics

Answer 38

* Lightning * Fuelling

Question 39

Dangers of electrostatics: Lightning

Answer 39

1. Negative cloud with excess electrons 2. Excess electrons flow to Earth as lightning 3. Building have lightning conductors to carry this to the ground to avoid damage to building

Question 40

Dangers of electrostatics: Refuelling

Answer 40

1. As fuel rubs against the hose, a static charge can build up. 2. If these excess electrons spark across the gap, an explosion can result 3. Bending wire allows the electrons to safely cross the gap