Electricity

Question 1

Circuit symbol for An LDR

Question 2

What is electric current?

Answer 2

the flow of electrical charge

Question 3

Equation that links charge, time and current. Give units.

Answer 3

charge = time x current
Q = t x I
charge = coulombs
current = Amp meters
Time = seconds

Question 4

Value of the current in a series circuit

Answer 4

current is the same all the way around the circuit

Question 5

What factors does the current in a circuit depend upon?

Answer 5

Resistance = R
potential difference = V

Question 6

Calculation for potential difference

Answer 6

potential difference = current x resistance
V = I X R

Question 7

What is the ohmic conductor

Answer 7

When the potential difference is directly proportional to the Current (as the p.d increases so does the current) To keep this constant they need the same constant temperature

Question 8

can resistance change?

Answer 8

In some resistors the value of R remains constant, while in others the value can change as the current changes e.g ohmic conductors

Question 9

do components in a circuit affect resistance?

Answer 9

The resistance of components such as lamps, diodes, thermistors
and LDRs is not constant; it changes with the current through the
component.

Question 10

What happens to the resistance of a filament lamp as the temperature increases?

Answer 10

The filament of the lamp increases, producing more metal ions which creates resistance.

Question 11

what happens to a thermistor as temperature increases?

Answer 11

Thermistor (a type of resistor that is reliant on temperature) resistance will decrease

Question 12

two examples of when a thermistor may be used

Answer 12

In a thermostat, to turn on heat when below a certain temperature
In a freezer to turn on the cooler when temperature becomes too high

Question 13

what happens to an LDR when light intensity decreases?

Answer 13

LDR’s resistance increases

Question 14

Applications for LDR

Answer 14

Street lights - turn on when it gets too dark
When there are low enough light levels it gains enough current to turn on

Question 15

How does potential difference vary across series and parralell?

Answer 15

Series - P.D Is shared between components
Parallel- P.D across components is the same

Question 16

current in a series circuit

Answer 16

Current is the same all the way around as there is only one path

Question 17

How to connect an ammeter into a circuit to measure current?

Answer 17

In series to the component they are measuring

Question 18

How should you connect a voltmeter to a circuit to measure potential difference?

Answer 18

In parallel to the component they are measuring

Question 19

In series what is the total resistance?

Answer 19

Total resistance is equal to the
resistance of the two components
Rtotal = R2 + R 1

Question 20

Is main’s electricity an A.C or D.C supply ?

Answer 20

Main’s electricity is an A.C
A.C = alternating current
D.C = Direct current

Question 21

what is a.c and d.c?

Answer 21

Alternating current = current that continuously changes direction
Direct current = one directional flow of current

Question 22

What is the frequency and voltage of the U.K mains electricity supply?

Answer 22

Frequency =50Hz
Voltage = 230V

Question 23

Which wires are used to connect appliances to the main electrcity supply?

Answer 23

Live
Neutral
Earth wires

Question 24

colour of earth wire

Answer 24

green and yellow

Question 25

colour of live wire

Answer 25

brown, used to complete the circuit, around 0 V

Question 26

colour of neutral wire

Answer 26

blue

Question 27

Why doesn’t the earth wire carry current?

Answer 27

so it an accident occurs current will flow to the ground instead of the appliance preventing electrocution

Question 28

Defintion of the live wire

Answer 28

carries A.C from the supply (usually at 230v ) Is connected to a fuse in the plug

Question 29

Equations for calculations of power in a circuit

Answer 29

P = I X V or P = I2 x R

power = watts
I= Amps
V= volts

Question 30

equation that links energy transferred, power and time

Answer 30

E = P XT
energy transferred = Joules
Power = watts
time = seconds

Question 31

equation that links energy transferred , charge flow and potential difference

Answer 31

energy transferred = charge flow × potential difference

charge flow = coulombs

Question 32

what are the factors that affect the amount of energy transferred to an appliance

Answer 32

1. the power of the appliance
2. how long the appliance is being used for

Question 33

describe the energy transfers in a torch

Answer 33

battery of the torch converts the chemical energy into electrical energy,
Lights transfers it into the light energy and also wasted thermal energy

Question 34

what things affect the power of a circuit

Answer 34

1. the potential difference in a circuit
2. the amount of energy transferred
3. the amount of current

Question 35

Purpose of the national grid

Answer 35

to link power stations to houses

Question 36

the two types of transformers used in the national grid

Answer 36

1. step up transformers
2. step down transformers

Question 37

what do step up transformers do?

Answer 37

Used to connect power stations to the transmission cables,
they also increase the potential difference and decrease the current

Question 38

what do step down transformers do?

Answer 38

connect tranformers to domestic houses and decreases potential difference so the electricity doesn’t blow up the house

Question 39

why do the transmission lines transfer electricity at high potentials

Answer 39

at high potential there is less current, less current means less energy is wasted as heat = more efficent