Electricity

Question 1

Does a circuit need to be opened or closed for an electrical charge to flow through?

Answer 1

Closed

Question 2

What is electric current?

Answer 2

Flow of electrical charge

Question 3

Equation for charge flow

Answer 3

charge flow= current x time

Question 4

What does the current depend on?

Answer 4

Resistance and Potential difference

Question 5

Equation for potential difference, current and resistance

Answer 5

potential difference = current x resistance

Question 6

How to investigate factors affecting resistance

Resistance in wires required practical

Answer 6

Attach crocodile clip to wire level with 0cm on ruler
Attach 2nd crocodile clip the wire e.g. 10cm away from first clip. Write down length
Close switch, record current and pd
Open switch, move 2nd cc 10 cm, record length, current, pd
Repeat
Calculate resistance R=V/I
Plot graph
should be straight line

Question 7

What are Ohmic Conductors

Answer 7

The resistance doesn’t change with the current. At a constant temp the current flowing through an ohmic conductir is directly proportional to the pd

Question 8

When is the resistance not constant?

Answer 8

Lamps, diodes, thermistors and LDRs, changes with the current through component

Question 9

What is the resistance of a filament lamp like?

Answer 9

Increases as the temperature of the filament increases

Question 10

Diode

Answer 10

The current through a diode flows in one direction flows in one direction only. The diode has a very high resistance in the reverse direction

Question 11

Thermistor

Answer 11

The resistance of. thermistor decreases as the temp increase

The applications of thermistors in circuited eg thermostat required

Question 12

LDR

Answer 12

resistance decreases as light intensity increase

Application of LDRs in circuits eg switching lights on when it gets dark is required

Question 13

For components connected in series…

Answer 13

There is the same current through each component
Total potential difference of the power supply is shared between the components
Total resistance of two components is the sum of the resistance of each component

Resistance= R1 + R2

Question 14

For components connected in parallel…

Answer 14

The potential difference across each component is the same
The total current through the whole circuit is the sum of the currents through the separate components
The total resistance of two resistors is less than the resistance of the smallest individual resistor

Question 15

If mains electricity ac or dc?

Answer 15

AC

Question 16

What is the frequency and voltage in the UK

Answer 16

50 Hz

230V

Question 17

What is ac?

Answer 17

The current is constantly changing direction. Positive and negative ends keep alternating

Question 18

What is dc?

Answer 18

Current flowing in the same direction

Direct voltage

Question 19

What colour is the live wire?

Answer 19

brown

Question 20

what colour is the neutral wire?

Answer 20

Blue

Question 21

What colour is the earth wire?

Answer 21

green and yellow stripes

Question 22

Explain the uses of the wire

Answer 22

live wire carries the alternating potential difference from supply. Neutral wire completes circuit. Earth wire is safety wire to stop applicants becoming live

Question 23

What is the pd between the live wire and earth?

Answer 23

230 V

Question 24

What is the pd of an earth wire?

Answer 24

0V only carries current if there is a fault

Question 25

Why can a live wire be dangerous?

Answer 25

Your body is at 0V so there would be a huge potential difference between you and the live wire causing an electric shock

Question 26

Equation for power

Answer 26

potential difference x current

current squared x resistance

Question 27

Equation for energy transferred

Answer 27

power x time

charge flow x pd

Question 28

What does the energy transfer depend on?

Answer 28

How long the appliance is switched on for and the leaker

Question 29

How is the potential difference related to energy transfer

Answer 29

when change in pd, energy transferred
Energy supplied to charge at power source to raise it through potential
Charge give up energy when it falls through any potential drop in component elsewhere in the circuit

Question 30

What is the national grid?

Answer 30

System of cables and transformers linking power stations to consumers.
Electrical power is transferred from power stations to consumers using national grid

Question 31

What are step up transformers?

Answer 31

Used to increase pd from power station to transmission cables for efficient transmission

Question 32

What are step down transformers?

Answer 32

Decrease the pd for domestic use at a save usable level

Question 33

How does static charge work?

Answer 33

When insulating materials rubbed against each other become electrically charged. Negatively charged electrons rubbed off one material onto other. Material gains electrons becomes negatively charged. Material loses electrons left with equal positive charge. When brought close together exert force on each other. Charge repel. Attraction and repulsion between 2 charged objects are examples of non contact force

Question 34

What is an electric field?

Answer 34

A charged object creates an electric field around itself. Electric field strongest close to charged object. Further away from charged object, weaker the field

Second charged object placed in field experienced a force. Force gets stronger as distance between object decrease

Question 35

I/V graph required practical

Answer 35

Set up the test circuit- look on camera roll
Begin to vary the variable resistor. Alters current flowing through circuit and potential difference across component
Take several pairs of readings from ammeter and voltmeter to see how potential difference across component varies as current changes. Repeat each reading twice more to get an average pd at each current
Swap over wires connected to cell, direction of current is reversed.
Plot a graph of current against voltage for component
I-V characteristics you get for an ohmic
conductor, filament lamp and diode.

Calculate resistance at any point on I-V characteristics by calculating R=V/I