Electricity

Question 1

What causes static electricity?

Answer 1

Friction causes the negative electrons to move from your hair to the balloon. Materials that gain electrons become negatively charged (the balloon), materials that lose electrons become positively charged (your hair)

Question 2

How do materials become electrically charged?

Answer 2

When insulating materials are rubbed against each other (using friction) they become electrically charged e.g. rubbing a balloon against your hair.

Question 3

What is current?

Answer 3

Current is the flow of charged particles, usually through a metal wire.

Question 4

What is potential difference?

Answer 4

Potential difference is how much energy is transferred by each charged particle

Question 5

What is resistance?

Answer 5

Resistance causes the battery’s chemical energy to be converted into thermal energy

Question 6

Charge equation

Answer 6

Charge(coulomb)= current(amps) X time(s)

Question 7

Energy transferred equation

Answer 7

Energy transferred(Joules)= potential difference(volts) X charge(coulomb)

Question 8

Potential difference equation

Answer 8

Potential difference(volts)= current(amps) X resistance(ohms)

Question 9

What is a filament lamp?

Answer 9

A filament lamp is an example of a non-ohmic conductor I.e. the current and potential difference are not directly proportional (unlike a resistor). The current passing through the filament causes the temperature to increase causing it to glow and further increase its resistance. As the temperature increases the resistance also increases I.e. it is more difficult for the electrons to get through the filament

Question 10

What is a diode?

Answer 10

Current will only flow through a diode in one direction. The diode has very high resistance in the reverse direction.

Question 11

What is an ohmic conductor?

Answer 11

The current through an ohmic conductor (at constant temperature) is directly proportional to potential difference so you get a straight line. Ohmic conductor- e.g. resistor

Question 12

What is a light dependent resistor?

Answer 12

An LDR is a resistor that is dependent on the intensity of light.
In bright light the resistance falls, in darkness the resistance is highest.
They have lots of applications including automatic night lights, outdoor lighting and burglar detectors.

Question 13

What is a thermistor?

Answer 13

A thermistor is a temperature dependent resistor. In hot countries, the resistance drops. I’m cool countries, the resistance goes up.
Thermistors make useful temperature detectors, e.g. car engine temperature sensors.

Question 14

What are the properties in a series circuit?

Answer 14

Battery p.d is SHARED around the circuit
Total current is the SAME all around the circuit
Current is measured using ammeters that are placed in series in the circuit
In series circuits there is only one route for the electrons to travel around the circuit

Question 15

What are the properties in a parallel circuit?

Answer 15

Battery p.d is the SAME for all components
Total current is SHARED between all branches in the circuit
The total resistance of the circuit is LESS THAN the smallest resistance
Potential difference is measured in voltmeters that are placed in parallel circuit
In parallel circuits there are two or more routes for the electron to travel around the circuit
The total resistance of the circuit is the SUM of each of the resistances

Question 16

What is a Direct Current?

Answer 16

One that always flows around the circuit in the same direction. Cells and Batteries are sources of direct current because their voltages remain constant over time

Question 17

Uses of a direct current:

Answer 17

Remote control, phone, cells and batteries are sources of DC because their voltages remain constant over time.

Question 18

What is an alternating current?

Answer 18

One that is constantly changing direction. Mains electricity is a source of alternating current because its voltage alternates (changes) over time.

Question 19

What is the voltage and frequency of the mains electricity in the UK?

Answer 19

In the UK the mains electricity supply has a voltage of about 230V and a frequency of 50Herts

Question 20

What does oscilloscope mean?

Answer 20

To look at the direct and alternating current

Question 21

What does power mean?

Answer 21

The amount of energy transferred every second

Question 22

Power equation

Answer 22

Power(W)= energy transferred divided(J) divided by time(S)

Question 23

Power equation

Answer 23

Power(W)= current(A) X potential difference(V)

Question 24

Power equation

Answer 24

Power(W)=current(Asquared) X resistance(ohms)

Question 25

What is the difference between UK and European plugs?

Answer 25

UK plugs have 3 pins but European plugs only have 2. This is because the European plugs don’t have an earth wire because they’ve got double insulation so you can’t get electrocuted so there is no need for an earth wire in European plugs.

Question 26

How do large amounts of electricity not melt the cable?

Answer 26

An appliance that needs more power will have a thicker cable (to stop it from melting!!)

Question 27

What colour and position is the earth wire?

Answer 27

The earth wire is positioned at the top of the plug. Safety wire, sends current to ground if a fault occurs. Green and yellow

Question 28

What colour and position is the live wire?

Answer 28

Positioned to the right of the plug. Provides alternating potential difference. Provides 230V. Brown.

Question 29

What colour and position is the neutral wire?

Answer 29

Positioned at the left of the plug. Completes the circuit and carries away the current. Has almost 0V. Blue

Question 30

What is the national grid?

Answer 30

A giant system of cables and transformers that covers the UK and connects power stations to consumers.

Question 31

What does a step-up transformer do?

Answer 31

Increases voltage, decreases current, reduces energy lost due to resistance in cables.

Question 32

What is the voltage of the cables?

Answer 32

40,000V

Question 33

What does the step-down transformer do?

Answer 33

Reduces voltage to 230V so it’s safe to use in our homes

Question 34

Why is underground cables more safe than the overhead system?

Answer 34

Because all distribution wiring is placed underground and there are little chances of any hazard.

Question 35

Does the underground or overhead system have more initial costs?

Answer 35

The underground system is more expensive due to the high cost of trenching, conduits cables, manholes and other special equipment.

Question 36

Which system is harder to repair and more likely to suffer accidental damage?

Answer 36

Underground system because if a fault occurs in the underground system, it is difficult to locate and repair. Also suffer more frequent accidental damage from construction projects and other digging activities.

Question 37

Why do electrical appliances waste energy?

Answer 37

Because the electrical components inside them have a small resistance- this causes a small heating effect.
Electrical devices with motors (e.g. hairdryers) also waste energy due to friction between the moving parts- this heat is transferred to the surroundings.

Question 38

Efficiency equation

Answer 38

Efficiency= useful power output divided by total power input X100

Question 39

Why does the national grid use a high PD and a low current?

Answer 39

To transmit the huge amount of power needed, you need either a high potential difference or a high current. The problem with a high current is that you lose loads of energy as the wires heat up and energy is transferred to the thermal energy store of the surroundings. It’s much cheaper to boost the PD up really high and keep the current as low as possible. This makes the national grid an efficient way of transferring energy.