Electricity

Question 1

Ring main circuits consist of 3 types of wires:

Answer 1

• Live wire
• Neutral wire
• Earth wire

Question 2

Advantage of ring main circuits:

Answer 2

Reduces the amount of wiring needed

Several applications in different parts of the same room can be connected to the mains with minimum wiring

Question 3

How does a fuse work?

Answer 3

A fuse has a thin wire with a low melting point. So, if a large current passes through it, the wire melts breaking the circuit and stopping the flow of current to the device preventing an electric shock or fire

Question 4

How does a circuit breaker/ trip switch work?

Answer 4

If too large a current passes through it the switch automatically opens breaking the circuit. Once the fault has been corrected, the switch is reset

Question 5

How does earth wiring prevent an electric shock?

Answer 5

It is attached to the metal casing of an appliance so that if there is a break/ damage in the live wire, it provides a low resistance path for the current

Question 6

Do double insulated appliances need earth wiring?

Answer 6

NO

Question 7

Why should the switch be placed in the live wire?

Answer 7

So that when the switch is open, electricity is not passed through the wire to the appliance

Question 8

How is the heating effect of a current used in appliances?

Answer 8

The wires of a heating element have high resistance so current builds up in the wires and energy is transferred and the element heats up

Question 9

Write the equation relating to power, voltage, and current

Answer 9

P = I x V

Question 10

How to calculate the total energy transferred by an appliance?

Answer 10

E = P x T

E = I x V x T

Question 11

What is an alternating voltage?

Answer 11

A voltage that is continuously changing its value and direction

Question 12

What type of voltage do cells and batteries use?

Answer 12

Direct current

Question 13

What is an electric current?

Answer 13

The flow of charge carried by electrons

Question 14

The direction of flow of charge in a conventional current:

Answer 14

From +ve terminal to the -ve terminal

Question 15

One coulomb is equal to the charge carried by ________ electrons

Answer 15

6 x 10¹⁸

Question 16

Current is measured using ______ in units called ______

Answer 16

Ammeter

Amperes (A)

Question 17

What is the relationship between the electric charge, current, and time

Answer 17

Q = I x t

Question 18

What is voltage?

Answer 18

The amount of energy supplied to each coulomb of charge

Question 19

What does the voltage across a component indicate?

Answer 19

It indicates the energy transferred by the component (as a coulomb passes through it)

Question 20

Write the equation for the relationship between energy transferred, charge, and voltage

Answer 20

E = Q x V

E = I x t x V

Question 21

Draw circuit symbols for:

a) Diode
b) Variable resistor
c) Thermistor
d) LDR

Answer 21

(a) —ⅼ◀—
(b) ↗
(d) ↘↘

Question 22

What are the features of a series circuit?

Answer 22

• One switch placed anywhere in the circuit can turn all the bulbs on and off
• If any one bulb breaks, causes the circuit to become incomplete and others will also not work
• The voltage is shared between the bulbs so their brightness reduces if a bulb is added
• The current is the same throughout the circuit

Question 23

What are the features of a parallel circuit?

Answer 23

• A switch can be placed in different parts of the circuit to turn the bulbs on and off individually or all together
• If one bulb breaks, only the bulbs on the same circuit will not work
• The voltage is equal in all the branches so the bulbs’ brightness remains the same if a bulb is added
• The current is not the same throughout the circuit. The current entering a junction is equal to the current leaving the junction

Question 24

Voltage, current, and resistance are related as follows:

Unit of resistance:

Answer 24

V = I x R

Ohms Ὼ

Question 25

What is the function of fixed resistors in a circuit?

Answer 25

It controls the sizes of currents and voltages in a circuit

Question 26

What is the function of variable resistors in a circuit?

Answer 26

Allow you to alter the resistance

Can be used as a dimmer switch, to control the speed of a motor

Question 27

Where are thermistors used?

Answer 27

In fire alarms, freezers, and computers

Question 28

Where are LDRs used?

Answer 28

In photographic exposure equipment, automatic lighting controls, and burglar alarms

Question 29

How does a Diode work?

*LEDs

Answer 29

A type of resistor that has a low resistance when current is flowing in one direction but a high resistance if the current is flowing through it in another direction

*These diodes light up when charges flow through them

Question 30

Where are diodes used?

Answer 30

In rectifier circuits which convert a.c to d.c

Question 31

What should be the electrical conductivity of two objects that gain an electric charge by friction?

Answer 31

They should be electrical insulators

Question 32

How does electrostatic spray painting work?

Answer 32

The metal nozzle of the spray is going to be +vely charged and so as the pant particles leave, they will repel and form a thin spray.

The bicycle frame is connected to a wire that gives it the opposite charge (-ve)

They’ll be attracted to the bicycle frame’s surface

Question 33

How do inkjet printers work?

Answer 33

Each drop of ink is given a charge so that as it falls between a pair of deflecting plates, electrostatic forces direct it to the correct position on the paper.

The charges on these plates change 100s of times per second to direct each drop of ink to its specific position, forming pics and texts.

Question 34

How do photocopiers work?

Answer 34

+ve charge is sprayed onto a turning drum covered in selenium. A bright light is shone on the paper to be copied. The white parts of the paper reflect light onto the drum, the selenium loses charges in places where light is reflected.

A -vely charged toner is blown across the drum and attaches to the +vely charged parts of the drum.

The paper is pressed against the drum and picks up the pattern of the toner. The toner is permanently fixed in place by heating the paper

Question 35

How do electrostatic precipitators work?

Answer 35

As the smoke rises up the chimney, it passes through a mesh of highly charged wires.

A -ve charge is induced on the dust and ash particles, as these particles rise they are attracted to large metal earthed plates

Question 36

Problems with static electricity:

Answer 36

• The risk of electrocution (from lightning)

- The risk of a fire or explosion (due to a spark close to flammable gas or liquid).