Paper 1 Electricity

Question 1

A direct current flows in how many directions?

Answer 1

A direct current flows in ONE direction only
eg car batteries, solar cells

On a Voltage-time graph is would appear as a STRAIGHT HORIZONTAL line

Question 2

What direction does an ALTERNATING CURRENT flow>

Answer 2

An ALTERNATING CURRENT regularly CHANGES direction

On a Voltage-time graph is would appear as a CURVE alternating between + and - line

Eg

Question 3

What wires are good conductors?

Answer 3

Copper wires are good conductors

Question 4

What is a good insulator?

Answer 4

Plastic is a good insulator

Question 5

BROWN wire

Answer 5

. LIVE - to right
. Carries 230V
. Brown wire

Question 6

Blue wire

Answer 6

. NEUTRAL wire
. Blue wire
. It completes the circuit at 0v

Question 7

Yellow & Green

Answer 7

. Yellow & Green is earth wire
. O v
. There for safety
. Does not form part of the normal circuit

Question 8

What could happen if no earth wire?

Answer 8

Without an earth wire … ELECTROCUTED

Question 9

ENERGY =

Answer 9

ENERGY = P x t
(J)             = (W) (s)

Question 10

POWER =

Answer 10

POWER = V x I
(W)         = (potential difference) x (current in Amps)

Question 11

What is the MAINS VOLTAGE in this country?

Answer 11

. The MAINS VOLTAGE in this country voltage in this
country is 230 V.

. The current ALTERNATES will a FREQUENCY of 50 hertz (Hz)
. ac supply (alternating current

Question 12

Which wire does the fuse connect to?

Answer 12

The fuse connects to the LIVE wire

Question 13

What power is transmitted by a 5 A current through a 10 Ω resistor?

Answer 13

250 W is the power transmitted. P = I²R, P = 25 × 10 = 250 W. Don’t forget to square the current.

Question 14

What is a step down transformer?

Answer 14

A step down transformer…

A step down transformer INCREASES the current and LOWERS the voltage.

Question 15

Electrical appliances - type of energy

Answer 15

Electrical appliances - type of energy
. CHEMICAL (from power stations)
. KINETIC - to start the fan or oven

Question 16

energy = power × time

Answer 16

Energy = POWER x TIME

(s)

Question 17

P = V x I

Answer 17

P = V x I

Power (P) is measured in watts (W)
potential difference (V) is measured in volts (V)
current (I) is measured in amps (A)

Question 18

What are TRANSFORMERS used for?

Answer 18

Transformers are used to CHANGE VOLTAGES & CURRENTS in transmission lines.

Question 19

How can the power transferred be kept the same?

Answer 19

As the power transferred must stay the same:

. increasing voltage decreases current
. decreasing voltage increases current

Question 20

Transmission through thick cables held up by pylons

Answer 20

power = current2 × resistance

P - I2 x R

power (P) is measured in watts (W)
current (I) is measured in amps (A)
resistance (R) is measured in ohms (Ω)

Question 21

Electric current created chemically is always …

Answer 21

Electric current created chemically is always DIRECT.

Question 22

Alternating current is generated using …

Answer 22

Alternating current is generated using MAGNETS

Question 23

The earth wire provides …..

Answer 23

The earth wire provides a LOW RESISTANCE path to ground. A high resistance path would not cause the fuse to melt.

Question 24

Power =

Answer 24

Power = E/t

Question 25

Efficiency =

Answer 25

useful energy transfer/total energy transfer

Question 26

or Efficiency =

Answer 26

useful power output/total power input

Question 27

An efficiency of 0.5 or 50% means …

Answer 27

50% efficiency = half the energy is useful but half is wasted.

Question 28

Neutral/blue wire does what?

Answer 28

Neutral wire carried the current away from the appliance.

Question 29

Definition of National Grid

Answer 29

Links power to homes and business by cables and transformers transferring Electrical Power

Question 30

Power Station

Answer 30

Transfers the energy supply into electrical energy 25,000V

Question 31

Step up transformer

Answer 31

Step up transformers INCREASE the VOLTAGE from the POWER STATION to the TRANSMISSION CABLES

Question 32

Transmission cables

Answer 32

Transmission cables - TRANSFER the electricity

Question 33

Step down transformers

Answer 33

Step down transformers - reduce the voltage from the TRANSMISSION CABLES for DOMESTIC USE (houses & shops) to 230V