Electricity

Question 1

What is current?

Answer 1

Flow of electrical charge

Question 2

What is potential difference?

Answer 2

The driving force that pushes charge around

Question 3

What is resistance?

Answer 3

Anything that slows charge down - ohms

Question 4

What two factors does the current in a component depend on?

Answer 4

• resistance (greater resistance = smaller current)
• potential difference (for a fixed resistance the greater the potential difference the larger the current

Question 5

What is the equation for charge flow?

Answer 5

Charge flow = current x time
Q = It
Q is measured in coulombs

Question 6

What is the size of the current equal to?

Answer 6

The rate of flow of charge

Question 7

What is the equation for potential difference?

Answer 7

V = IR

Question 8

What is the I-V characteristics of an ohmic conductor (resistor) at a constant temperature?

Answer 8

Current is directly proportional to the potential difference so the resistance does not change
The graph is linear

Question 9

What are the components with changing resistance when current through them varies?

Answer 9

• Filament lamp
• Diode
• LDR (light dependent resistor)
• thermistor

Question 10

What are the I-V characteristics for the filament lamp?

Answer 10

Current increases so temperature of the filament increases so resistance increases

Question 11

What are the IV characteristics of a diode?

Answer 11

High resistance in one direction so current only flows in the other direction

Question 12

What does resistance depend on in a light dependent resistor?

Answer 12

Light intensity
Has a lower resistance in brighter light
Used in automatic night lights

Question 13

What does the resistance in a thermistor depend on?

Answer 13

Temperature
Has a lower resistance in higher temperatures
Used in thermostats

Question 14

What is the current like in a series circuit?

Answer 14

The same everywhere

Question 15

What is the potential difference like in a series circuit?

Answer 15

The total p.d is shared across components

Question 16

What is the resistance like in a series circuit?

Answer 16

Sum of the resistance of the components

Question 17

What is the current like in a parallel circuit?

Answer 17

The total current is the sum of the current in each branch

Question 18

What is the p.d like in a parallel circuit?

Answer 18

The total p.d is the same throughout the circuit

Question 19

What is the resistance like in a parallel circuit?

Answer 19

The total resistance is smaller than the smallest resistor

Question 20

What does adding a resistor do in a series circuit?

Answer 20

increases total resistance

Question 21

What does adding a resistor do in a parallel circuit?

Answer 21

decreases total resistance

Question 22

What is alternating current?

Answer 22

Current that constantly changes direction and is produced by alternating voltage.
Supplied by mains

Question 23

What is direct current?

Answer 23

Current that always flows in the same direction and is produced by a direct voltage
supplied by batteries

Question 24

What are three facts about the UK mains?

Answer 24

• ac current
• frequency of 50 Hz
• voltage of around 230V

Question 25

What is the live wire?

Answer 25

Brown Has a p.d of 230V Provides alternating p.d from mains

Question 26

What is the neutral wire?

Answer 26

Blue Has a p.d of around 0 Completes the circuit

Question 27

What is the earth wire?

Answer 27

Green and yellow striped Has a p.d of 0 Stops appliance casing from becoming live - current only flows through earth wire when there is a fault

Question 28

How does an electric shock happen?

Answer 28

When coming in contact with a wire there is a large potential difference (body = 0V and wire - 230V) Large potential difference is produced across body Current flows through body Can cause injury or death A plug still may cause harm when turned off

Question 29

What happens when a live and earth wire come into contact?

Answer 29

Dangerous - may cause a fire

Question 30

What are the two equations for energy transferred?

Answer 30

Energy transferred = charge flow x p.d E = QV Energy transferred = power x time E = Pt

Question 31

What happens when charge flows?

Answer 31

Work is done and therefore, energy is transferred

Question 32

What does the amount of energy depend on in an appliance?

Answer 32

- Appliance's power - How long an appliance is on for

Question 33

What is power?

Answer 33

energy transferred per second

Question 34

What is a power rating?

Answer 34

Maximum safe power that an appliance can operate at

Question 35

What are the two equations involving current for power?

Answer 35

P = VI P = I2R power = current squared x r

Question 36

What is the national grid?

Answer 36

A system of cables and transformers that connect power stations to consumers

Question 37

Why is transferring a high current not efficient?

Answer 37

It would increase resistance and lead to a temperature increase. Heat loss to the surrounding (energy loss)

Question 38

What do step up transformers do and why?

Answer 38

They increase the potential difference so that there is a low current and therefore low resistance in the wire.

Question 39

What do step down transformers do and why?

Answer 39

They decrease the p.d to 230V so that it is safer in the mains.

Question 40

How does static electricity work?

Answer 40

Rub two insulating materials together Electrons move from one to the other Both materials have become electrically charged - equal and opposite charge on each Only electrons move (positive charge doesnt move)

Question 41

What is an electric spark?

Answer 41

The passage of electrons across a gap between a charged object and the earth (or earthed conductor) Gap is usually small

Question 42

How does an electric spark occur?

Answer 42

- Electric charge builds on an object - Potential difference between object and earth increases - When p.d is large enough there is a spark

Question 43

What is an electric field?

Answer 43

A region in which another charged object feels a force Created around any electrically charged object

Question 44

What do strong electric fields do?

Answer 44

They ionise air particles which can cause sparks

Question 45

What does it mean when field lines are close together?

Answer 45

The electric field is strong

Question 46

What happens when a charged object is placed in an electric field?

Answer 46

They experience a force - attraction or repulsion non contact force As distance between them decreases the force acting on them increases