Topic 2- Electricity

Question 1

What is electric current?

Answer 1

The flow of electrical charge

Question 2

What can be said abut current at any point in a single closed loop?

Answer 2

It is the same al every point in the circuit

Question 3

What 2 factors does current in a circuit depend on?

Answer 3

1. Potential difference

2. Resistance

Question 4

What is an ohmic conductor?

Answer 4

A conductor for which potential difference and current are directly proportional.
Resistance remains the same as current changes
Temperature must be constant

Question 5

List 4 components for which resistance is not constant as current changes (non-ohmic conductor)

Answer 5

1. Lamp
2. Diode
3. Thermistor
4. Light dependent resistor

Question 6

What happens to resistance of filament lamp as temp increases and why?

Answer 6

Resistance increases.
Ions in metal have more energy- vibrate more- more collisions with electrons as flow through metal- greater resistance to current flow

Question 7

What is different about current flow through a diode?

Answer 7

Current only flows in one direction. This is because resistance is high in other direction and prevents current flow

Question 8

What happens to resistance of thermistor as temperature increases?

Answer 8

Resistance decreases

Question 9

Give 2 examples of when a thermistor may be used

Answer 9

1. Thermostat to turn heater on below certain temperature

2. Freezer to turn cooler on when temperature becomes to high

Question 10

What happens to the resistance of an LDR as light intensity increases?

Answer 10

Resistance increases

Question 11

State a use of an LDR

Answer 11

Street lights- when light level becomes too low, light gains sufficient current to turn on

Question 12

What are 2 ways for a component to be connected to a circuit?

Answer 12

In series and in parallel

Question 13

How does PD vary when connected in series and in parallel?

Answer 13

Series; total PD shared between component

Parallel; PD across each component is the same

Question 14

If 2 resistors are in parallel, what can be said about their combined total resistance?

Answer 14

Total resistance is less than the resistance of the smallest resistor

Question 15

If 2 resistors are in series, what can be said about their combined total resistance?

Answer 15

Total resistance is equal to the sum of the individual resistances

Question 16

Describe the current in a series circuit?

Answer 16

Same at every point as it only has on path to follow

Question 17

Describe current in a parallel circuit

Answer 17

Current shared between different branches. Charge splits when it reaches a junction

Question 18

How should you connect an ammeter in a circuit?

Answer 18

Connect in series with component they are messing current through

Question 19

How should you connect a voltmeter in a circuit?

Answer 19

Connect in parallel to component they are measuring PD of

Question 20

Why is it better to connect lamps in parallel?

Answer 20

If one lamp blows, the rest will remain unaffected and can still receive current (circuit still complete)

Question 21

Is mains AC or DC?

Answer 21

Alternating current (AC)

Question 22

Define alternating and direct current.

Answer 22

AC: current that continuously changes direction at a specific frequency
DC: one directional current flow

Question 23

What is the frequency and voltage of the UK mains supply?

Answer 23

230V, 50Hz

Question 24

What are the wires in the cables that connect electrical appliances to the mains?

Answer 24

1. Earth wire
2. Live wire
3. Neutral wire

Question 25

What is insulation colour used on earth wire?

Answer 25

Green and yellow stripes

Question 26

What is the insulation colour used on the live wire?

Answer 26

Brown

Question 27

What is the insulation colour used on the neutral wire?

Answer 27

Blue

Question 28

When doesn’t the earth wire carry a current?

Answer 28

Under normal circumstances- doesn’t carry current

If fault occurs in appliance (casing becoming live) current will flow to ground

Question 29

What potential is the neutral wire?

Answer 29

0V

Question 30

What is PD between earth and live wires?

Answer 30

230 V

Question 31

What is the purpose of the neutral wire?

Answer 31

Completes circuit by connecting it back to mains supply

Question 32

For metal appliances, where is the earth metal connected to?

Answer 32

Metal casing of appliance

If live wire becomes lose and touches casing, current will flow through to prevent electrocution

Question 33

What factors does the amount of energy transferred by an appliance depend on?

Answer 33

1. How long appliance is being used for

2. Power of the appliance

Question 34

Describe energy transfers in a battery powered torch?

Answer 34

Battery converts Chemical energy converted into electrical energy
Bulb converts electrical energy into light (and heat- watse)

Question 35

What 3 things determine power of a circuit device?

Answer 35

1. PD across circuit
2. Current through circuit
3. Amount of energy transferred in a given time

Question 36

What is purpose of the national grid?

Answer 36

Link power statins to consumers so they have an electricity source

Question 37

What are the function of step up transformers?

Answer 37

Increase PD from power station to transmission cables

Question 38

What is the function of step down transformers?

Answer 38

Decrease PD from transmission cables to domestic buildings

Question 39

Why is PD raised?

Answer 39

High PD= low current

Lower the current, less energy is wasted as heat, so more efficient

Question 40

Why does PD then need to be decreased?

Answer 40

Safer- reduces risk of electrocution- appliances only designed for 230 V