Electricity

Question 1

what is the unit of current?

Answer 1

amperes

Question 2

what is current?

Answer 2

rate of flow of electrical charge

Question 3

What is the pd in a circuit?

Answer 3

driving force the pushes charge around

Question 4

What is the unit of pd?

Answer 4

volts

Question 5

What is resistance?

Answer 5

anything that slows the flow of the current down

Question 6

What is the unit for resistance?

Answer 6

ohms

Question 7

what is the unit for charge flow?

Answer 7

coulombs

Question 8

What factors affect resistance?

Answer 8

• whether the components are in series or parallel
• length of wire used

Question 9

what is an ammeter?

Answer 9

• measures current
• must be placed in series

Question 10

What is a voltmeter?

Answer 10

• measures pd
• must be placed in parallel

Question 11

Why does the resistance change through a diode or filament lamp?

Answer 11

• filament lamp- some energy is transferred to thermal energy stores and resistance increases with temperature so the higher the current the higher the resistance
• diode- depends on direction of current- high resistance if not flowing the right way

Question 12

What does the term ‘I-V characteristic’ mean?

Answer 12

a graph which shows how the current flowing through a component changes as the pd across it increases

Question 13

What is an ohmic conductor?

Answer 13

a resistor at a constant temperature

Question 14

What does LDR stand for?

Answer 14

light dependent resistor

Question 15

What is an LDR and what is it used for?

Answer 15

a resistor that depends on the intensity of light- bright light resistance falls
- automatic night lights, outdoor lighting and burglar detectors

Question 16

What is a thermistor and what is it used for?

Answer 16

a resistor that depends on temperature- in hot conditions the resistance falls
- useful temperature detectors (electronic thermostats)

Question 17

What is a series circuit?

Answer 17

a circuit where all the components are connected in a line, end to end- besides voltmeters

Question 18

What are the rules of a series circuit?

Answer 18

• pd is shared between all components
• current is the same everywhere
• resistance adds up
• cell pd adds up

Question 19

What are the rules of a parallel circuit?

Answer 19

• pd is the same across all components
• current is shared between branches
• adding a resistor reduces total resistance

Question 20

what is an ac supply?

Answer 20

has an alternating current produced by an alternating voltage in which the positive and negative ends keep alternating

Question 21

What is the UK mains supply?

Answer 21

an ac supply at around 230V

Question 22

What is the frequency of the ac mains supply?

Answer 22

50 Hz

Question 23

What supply dc?

Answer 23

cells and batteries supply direct current

Question 24

What are the three wires in a cable, what do they do and what is their voltage?

Answer 24

• Live wire- brown and provides alternating pd at 230V from mains supply
• Neutral wire- blue and it completes the circuit with current running through it at 0V
• Earth wire- green and yellow, for protecting the wiring and for safety- stops appliance casing from becoming live- doesn’t carry a current so is 0V

Question 25

Why can the live wire give you an electric shock?

Answer 25

your body is at 0V so if you touch the live wire a large pd is produced across your body and a current flows through you causing an electric shock

Question 26

what is the national grid?

Answer 26

a giant system of cables and transformers that covers the UK and connects power systems to consumers

Question 27

Is a high pd or high current better for the national grid?

Answer 27

You need a high pd or current for the high power output but higher current is expensive and inefficient due to losing so much energy to thermal energy stores SO increasing the pd is better as it decreases the current and therefore wasted energy and thus is more efficient

Question 28

How are transformers used in the national grid?

Answer 28

- STEP UP TRANSFORMER- used to increase the pd to 400,000V and decrease the current as it travels through the wires from the power stations - STEP DOWN TRANSFORMER- used to decrease pd and increase current to a safe level so it can be used by consumers

Question 29

What is static caused by?

Answer 29

when certain insulating materials are rubbed together, negatively charged electrons will be scraped off one and dumped on the other. This will leave the material electrically charged with a positive static charge on one and an equal negative static on the other

Question 30

Why can static cause sparks?

Answer 30

increased pd between object and earth so electrons can jump across the charged object and the earth

Question 31

What are the rules of drawing field lines?

Answer 31

- go from positive to negative - always at a right angle to the surface - closer together the lines are the stronger the field is