Electricity

Question 1

Equation for charge flow?

Answer 1

Charge = current x time

Question 2

Resistance and current relationship?

Answer 2

Greater resistance means lower current

Question 3

Equation for potential difference?

Answer 3

PD = current x resistance

Question 4

Examples of ohmic conductors?

Answer 4

Wires and resistors

Question 5

What is special about an ohmic conductor?

Answer 5

Resistance doesn’t change with current

Question 6

Relationship between current flowing through an ohmic conductor and PD at constant temperature?

Answer 6

Directly proportional

Question 7

Relationship between temperature and resistance?

Answer 7

Higher temperature = higher resistance

Question 8

How does resistance in a filament lamp work?

Answer 8

1. When charge flows through a filament lamp, energy is transferred to the lamp’s thermal energy store
2. Resistance increases with current in a filament lamp

Question 9

How does resistance in a diode work?

Answer 9

1. They will let current flow in one direction
2. They have very high resistance when current is reversed

Question 10

How do light dependant resistors change?

Answer 10

1. In bright light, resistance falls
2. In darkness, resistance increases

Question 11

2 uses of light dependant resistors

Answer 11

1. Burglar detectors
2. Automatic night lights

Question 12

How do thermistors change?

Answer 12

1. In hot conditions, resistance drops
2. In cool conditions, resistance increases

Question 13

2 uses of thermistors?

Answer 13

1. Thermostats
2. Car engine temperature sensors

Question 14

How do automatic lights work?

Answer 14

1. A bulb and an LDR are connected in parallel, so the pd across both will be high when its dark and the LDRs resistance is high
2. The greater the pd across a component, the more energy it gets
3. So a bulb connected in parallel to an LDR would get brighter as the room gets darker

Question 15

How does PD work in a series circuit?

Answer 15

The total pd is shared across all the components - all components’ pd adds to make the source pd

Question 16

How does current work in a series circuit?

Answer 16

Current is the same across all components

Question 17

How does resistance work in a series circuit?

Answer 17

Resistance adds up across components

Question 18

How does pd work across parallel circuits?

Answer 18

All components receive the full source pd

Question 19

How does current work in parallel?

Answer 19

Current is shared across branches - total current going in must = total current coming out

Question 20

How does resistance work in parallel?

Answer 20

1. Two resistors in parallel have a resistance less than the smallest resistor
2. Resistors in parallel have the same pd
3. Adding another loop gives current more directions to go, increasing total current flow in a circuit
4. Using V =IR resistance decreases

Question 21

What is the UK’s mains supply pd?

Answer 21

230V

Question 22

What is the frequency of the mains supply?

Answer 22

50Hz

Question 23

What is the brown wire and its function?

Answer 23

1. Live wire
2. Provides the alternating pd from the mains supply at 230V

Question 24

What is the blue wire and its function?

Answer 24

1. Neutral wire
2. Completes the circuit and carries current away - it has 0V

Question 25

What is the green and yellow wire?

Answer 25

1. Earth wire 2. Stops the appliance from becoming live by carrying current back to Earth when there's a fault

Question 26

How does an electric shock happen?

Answer 26

1. Your body is at 0V - so touching the live wire causes a large pd produced across your body and current flows through you 2. This is because your body provide a link between the supply and the earth and current flows through you

Question 27

How do kettles transfer energy?

Answer 27

Electrically from the mains supply to the kettle's thermal store

Question 28

How does a hand held fan transfer energy?

Answer 28

Electrically from the battery's chemical store to the kinetic energy store

Question 29

Equation for energy transferred and power?

Answer 29

Energy transferred = power x time

Question 30

What does the power rating of an appliance tell you?

Answer 30

Maximum amount of energy transfer per second

Question 31

Equation for energy transferred and charge flow?

Answer 31

Energy transferred = charge x pd

Question 32

Equation for power using pd?

Answer 32

Power = pd x current

Question 33

Equation for power using current?

Answer 33

P = I^2 x resistance

Question 34

2 ways power stations can meet high demand?

Answer 34

1. They run well below their maximum power output 2. Lots of small power stations which can be set up quickly

Question 35

Purpose of a step up transformer?

Answer 35

1. To increase pd and decrease current to minimise energy loss when the current moves along the wires

Question 36

Purpose of a step down transformer?

Answer 36

To decrease pd and increase current For maximum current to get to a home

Question 37

How does a cloth become positively charged when rubbed against a polyethene rod?

Answer 37

1. Negatively charged electrons are scraped off of the cloth and dumped onto the rod 2. This leaves the cloth with less electrons and a positive charge, and the rod with a negative charge

Question 38

How does too much static cause a spark?

Answer 38

1. As electric charge build on an object, the pd between the object and the earth increases 2. If the pd gets large enough, electrons can jump across the gap between the charged object and the earth

Question 39

How can electrostatic attraction/ repulsionbe shown?

Answer 39

Suspend a rod with a known charge from a string and hold another object with the same charge near the rod will repel the rod. Opposite charges will attract.

Question 40

3 points for drawing an electric field.

Answer 40

1. Positive to negative 2. Right angle to the surface 3. Closer lines = stronger field

Question 41

What causes electrostatic forces?

Answer 41

Electric fields interacting

Question 42

Explain sparks in terms of electric fields?

Answer 42

1. When pd is big enough, electrons jump across the gap between earth and the charged object 2. High pd causes a strong electric field between the two 3. Strong electric fields cause electrons to be removed from air particles 4. Ionized air is a great conductor so a current flows through it