electricity

Question 1

what is current

Answer 1

The rate of flow of charge

Question 2

What equation links charge, current and time?

Answer 2

charge = current x time    
(Q = I x t)

Question 3

What is potential difference?

Answer 3

The energy transferred per coulomb of charge between two points.

Question 4

Where should an ammeter and voltmeter be placed in a circuit?

Answer 4

Ammeter in series with the component

Voltmeter in parallel with the component

Question 5

What is resistance?

Answer 5

Resistance makes it harder for the current to flow.

Question 6

What equation links current, potential difference and resistance?

Answer 6

potential difference = current x resistance

V = I x R

Question 7

What is the relationship between pd and current through a fixed resistor?

Answer 7

They are directly proportional.

Question 8

Why does the resistance through a filament lamp increase as the pd increases?

Answer 8

As pd increases, current increases.
When current increases, more electrons flow.
When electrons flow, they collide with ions and other electrons.
This transfers energy to the ions, increasing the temperature.
As the temperature increases, the ions vibrate more.
This causes more collisions between the electrons and the ions, making it harder for the electrons to flow.

Question 9

What is a thermistor?

Answer 9

A resistor that decreases in resistance as the temperature increases.

Question 10

What is an LDR?

Answer 10

A resistor that decreases in resistance as the light intensity increases.

Question 11

Compare series and parallel circuits.

Answer 11

Series circuits
Current same at every point

pd shared between components
(Component with bigger resistance has bigger share of pd)
Total resistance is the sum of the individual resistors

Parallel circuits
Current shared between branches
(Branch with less resistance has bigger share of current)
pd across each branch is the same as the pd across the cells

Total resistance is less than the smallest resistor

Question 12

What is a diode?

Answer 12

A component that only allows current to flow in one direction because the resistance is so high in the opposite direction

Question 13

What equation links charge, energy transferred and potential difference?

Answer 13

energy = charge x pd

E = Q x V

Question 14

What equation links current, potential difference and power?

Answer 14

power = current x pd

P = I x V

Question 15

What equation links current, power and resistance?

Answer 15

power = current2 x resistance

P = I2 x R

Question 16

What is the difference between a direct current and an alternating current?

Answer 16

Direct current flows in one direction only

Alternating current constantly changing direction

Question 17

What is the voltage and frequency of UK mains electricity?

Answer 17

230V, 50Hz

Question 18

What colour are each of the three wires in a plug?

Answer 18

Live wire is brown
Neutral wire is blue
Earth wire is yellow and green

Question 19

What is the role of the three wires in the plug?

Answer 19

Live wire brings electricity into the appliance at 230V
Neutral wire completes the circuit, electricity at 0V
Earth wire takes current away from the appliance if there is a fault.

Question 20

How do the earth wire and fuse work together?

Answer 20

Earth wire has low resistance so in event of the live wire becoming loose, current surges down the earth wire.
This blows the fuse, breaking the circuit.
This prevents appliance fires

Question 21

Why do some appliances only have two wires?

Answer 21

Appliances with a plastic case (double insulated) don’t need an earth wire because the case doesn’t conduct electricity so can’t become live.

Question 22

What is the National Grid?

Answer 22

The network of power lines connecting the power stations to homes and industry.

Question 23

Describe the role of step-up transformers in the National Grid.

Answer 23

Step-up transformers increase the voltage
This decreases the current flowing
This reduces energy losses due to heating of the power lines
Increasing the efficiency

Question 24

Describe the role of step- down transformers in the National Grid.

Answer 24

Step-down transformers decrease the voltage

Making it safer to use in our homes

Question 25

What causes an object to become charged?

Answer 25

When two insulating materials are rubbed together
Friction causes electrons to be transferred from one object to the other
The object gaining electrons becomes negatively charged
The object losing electrons becomes positively charged

Question 26

What happens when objects with the same or opposite charges are brought together?

Answer 26

Objects with the same charge repel each other

Objects with opposite charges attract each other

Question 27

What is an electric field?

Answer 27

The area around a charged object where a force will be exerted?

Question 28

what causes charged objects to spark?

Answer 28

If charge builds up the potential difference between the object and earth becomes great enough for the charge to jump, pulling electrons off air particles.