2.3 And 2.4

Question 1

What is electrical resistance?

Answer 1

Electrical resistance is when a component resists or tries to stop the current flowing through it, the bigger the resistance the smaller the current produced by a particular voltage

Question 2

How do you get the total resistance in a series circuit?

Answer 2

To get the total resistance of a circuit you add the individual resistances of each component together

Question 3

How do you find the total resistance of in a parallel circuit If the resistors are equal

Answer 3

If 2 resistors of the same value are in parallel, then the total resistance is half of the value of one them, if three resistors have the same value in parallel then the total resistance is one third of them

Question 5

How do you find the total resistance in a parallel circuit if the resistors are unequal?

Answer 5

1/R1 + 1/R2 + 1/R3 then flip it

Question 6

What are the factors affecting resistance?

Answer 6

1. The metal or substance used (type of material )
2. The length of the wire ‘L’
3. The cross-sectional area of the wire ‘A’
4. Temperature of the wire

Question 7

Describe how you would investigate how the resistance of a metallic conductor at a constant temperature depends on length ?

Answer 7

• Firstly you would set up the circuit
• Use 10cm of wire and make sure the variable resistor is set to 1V
• Record the voltage and current
• Calculate the resistance using ohms law (V=IR)
• change the length by 10cm
• let the wire cool in between length changes to keep the temperature constant
• Repeat for 20,30,40 and 50 cm

Question 8

What is the power of an appliance

Answer 8

The power of an appliance is the rate at which the energy is transferred from one form to another and it is measured in watts. W

Question 9

What is the equation for energy ?

Answer 9

Energy (J) = Power (W) x Time (S)

Question 10

What is the equation for calculating power ?

Answer 10

P (W) = I (A) x V (V)

Question 11

What is a useful equation for energy?

Answer 11

Energy = Voltage X Current x Time

Question 12

What is direct current ?

Answer 12

Direct current is when current only flows in one direction, batteries and cells supply this

Question 13

How is direct current drawn ?

Answer 13

As a straight horizontal line

Question 14

What is alternating current

Answer 14

Alternating current is when current flows backwards and forwards constantly changing direction, mains electricity is a type of supply

Question 15

Give an example of alternating current ?

Answer 15

Mains electricity

Question 16

Why do mains provide an alternating current

Answer 16

Every mains has a live wire and a neutral wire.
The current through a mains appliance alternates.
The mains supply provides an alternating voltage between the two wires

Question 17

What does the mains voltage change from and what is the average value ?

Answer 17

The mains voltage changes from -320 to +320 V.
The average value of this voltage is 230 V

Question 19

What does an oscilloscope measure ?

Answer 19

An oscilloscope can be used to display the voltage of both alternating and direct current

Question 20

How is electricity in the home measured ?

Answer 20

Units used are kilowatt hours (kWh) sometimes known as ‘units’

Question 21

How many joules is one kWh ?

Answer 21

1kWh = 3 600 000J

Question 22

What is the energy equation for electricity in the home

Answer 22

E is in kWh =P is in kW x T but time is in hours

Question 25

What is a one-way switch ?

Answer 25

A one way switch is a basic electrical device used to operate household electrical or electronic equipment and it can connect one point to the electrical circuit and disconnect the other at the same time

Question 29

How does a one way switch work ?

Answer 29

- Two switches are controlling one light - Turning or flicking a switch changes the branch - If they are on the same branch the bulb is on - If they are not on the same branch the bulb is off

Question 30

What is the UK mains supply in volts ?

Answer 30

The UK mains supply is about 230 volts

Question 31

What colour is the earth wire ?

Answer 31

Yellow and green striped

Question 32

What colour is the Live wire

Answer 32

Brown

Question 33

What colour is the neutral wire?

Answer 33

Blue

Question 34

Where is the neutral wire located in the plug ?

Answer 34

Left

Question 35

Where is the live wire located in the plug ?

Answer 35

Right

Question 36

Where is the earth wire located in the plug?

Answer 36

At the top

Question 37

What is the cable made up of ?

Answer 37

Two or three inner cores of copper as copper is a good conductor - Outer layers of plastic because it is a good insulator - Two core cables are used for appliances that have plastic cases (no earth wire)

Question 38

What does the plug have ?

Answer 38

- A plastic or rubber case as these are good insulators - Pins that are made of brass as this is a good conductor and doesn't rust or oxidise - A fuse - An earth pin - A cable

Question 39

Why is the longest pin of the plug designed for ?

Answer 39

The longest pin of the plug is designed to make contact with the earth wire of the wall socket so that an appliance is automatically earthed when you plug it in

Question 40

What is the fuse ?

Answer 40

The fuse is a thin piece of wire which melts (blows) when a certain amount of current flows through it. (Has a low melting point) It protects the device by cutting the current.

Question 41

Why must a fuse which allows too much current not be placed in the plug ?

Answer 41

A fuse which allows too much current to flow must not be placed in the plug as this could cause an electrical fire and the fuse doesn't protect the user of the appliance as it takes 1 or 2 seconds for the fuse to melt

Question 42

What should the fuse always be ?

Answer 42

The fuse should always be just above the normal working current

Question 43

Why is the earth wire installed

Answer 43

This is installed if a fault occurs in the wiring and is connected to the ground of your home so if a live wire comes loose and touches the metal surface of an electrical advice, a current will flow. The current will flow through the earth wire and cause an overload. the excess current will flow through the fuse causing it to melt

Question 44

What does the earth wire prevent?

Answer 44

The earth wire prevents electricity from the live wire being conducted through the surface

Question 45

What is meant if an appliance is double insulated?

Answer 45

Appliances which are double insulated are encased in plastic and connected only to a cable with a live and neutral wire. Any metal attachments that a user might touch are fitted into a plastic case so they do not make a connection to the motor or any other electrical parts