Topic 2- Electricity

Question 1

What are the hazards of frayed cables?

Answer 1

They can give an electric shock if the live wire is exposed.

Question 2

What are the hazards of long cables?

Answer 2

They are a trip hazard

Question 3

What are the hazards of damaged plugs?

Answer 3

They can expose people to high voltages.

Question 4

What are the hazards of having water around sockets?

Answer 4

Water conducts so it can give electric shocks.

Question 5

What are the hazards that come with pushing metals into objects?

Answer 5

They can give electric shocks.

Question 6

What is the use of insulation?

Answer 6

It provides a protective layer around electrical wires to prevent the conduction of electricity in an electric field.

Question 7

What is double insulation and what is the use it?

Answer 7

This is when the actual product is placed in an insulated case (e.g.plastic) so that if current/electricity comes into contact with the object, there’ll be no hazards.

Question 8

Why are electrical appliances earthed?

Answer 8

It creates a safe route for current to flow through when it is in excess. It flows through the live wire, through the case and out down to the earth wire to disperse the excess current.

Question 9

What is the purpose of having a fuse in electrical circuits ?

Answer 9

When there is excess current, the excess heat from the current melts the fuse. This cuts off the live supply, isolating the appliance so it is impossible to get an electrical shock.

Question 10

What is the purpose of having a circuit breaker in electrical circuits?

Answer 10

When there is excess current, they switch off, breaking the circuit and preventing any more current from flowing.

Question 11

What are the differences between fuses and circuit breakers?

Answer 11

• Fuses melt when there is too much current, but circuit breakers detect the surge and switch off.
• Fuses have to be replaced if they melt, but circuit breakers can be reset after they have turned off.
• Fuses melt when there is too much current but circuit breakers break the circuit as soon as there is a current surge.

Question 12

What happens when current is flowing through a resistor and whah time of appliances use this theory?

Answer 12

When there is current flowing in a resistor, heat is produced. As a result of this energy transfer, the resistor is heated. This heating effect can be used in domestic appliances such as heaters/ hair dryers.

Question 13

Equation for electrical power?

Answer 13

Power= current X voltage

Question 14

Equation for electrical energy transferred

Answer 14

Energy transferred= current X voltage X time.

Question 15

What is the UK’s mains supply?

Answer 15

240 V

Question 16

What is A.C. current?

Answer 16

Alternating current. This means that the directing of the current keeps changing and its current can be increased or decreased by using a transformer.

Question 17

What is D.C. supply?

Answer 17

Direct current. This means that the current only flows in one direction.

Question 18

What are parallel circuits suitable for and why?

Answer 18

Lighting in houses.
Components in parallel circuits can be independently controlled and if one component breaks, the others can still work. The voltage is the same throughout whilst the current is shared.

Question 19

What are series circuits suitable for and why?

Answer 19

Very rarely used in items…e.g. Fairy lights.
Components in series circuits cannot be independently controlled and if one component breaks, the circuit will stop working.
As there are less wires in series, the product is cheaper.

Question 20

How is current distributed in series circuits?

Answer 20

The current in series circuits is the same throughout. This means that if you divide the total voltage of the components by the resistance of them all, you get the current.
I= V/R

Question 21

Describe and explain the shape of an I-V graph for a filament lamp.

Answer 21

As current is passed through the metal lamp, the temperature of it increases. This means that particles have more kinetic energy, so they collide more. This creates a high resistance.
The gradient of the line is the reciprocal of its resistance, so the line is curved and flattens out towards the end.

Question 22

Describe and explain the I-V graph for a piece of wire.

Answer 22

The current through a wire is proportional to the voltage provided that the temperature is constant. (Line through the origin)

Question 23

Describe and explain the I-V graph for resistors in general.

Answer 23

The current through a resistor is proportional to the voltage at a constant temperature.

(Different resistors have different resistances, but overall, it is always a straight line through the origin)

Question 24

Describe and explain the shape of an I-V graph for a diode.

Answer 24

The current only flows in one direction so there is a straight line under the x-axis until around 0.7V where it shoots up as there is a current.

Question 25

How can you increase the resistance of a circuit?

Answer 25

Have many components or use components with high resistance.

Question 26

How can you decrease the resistance of a circuit?

Answer 26

Decrease the number of components in the circuit or use components with low resistances.

Question 27

What is an LDR and describe why its resistance varies.

Answer 27

An LDR is a light dependant resistor. As the light intensity increases, the resistance decreases. The dimmer the light, the more resistance there is.

Question 28

Describe how a thermistor's resistance varies.

Answer 28

As the temperature increases, the resistance of the thermistor decreases. As the temperature decreases, the resistance increases.

Question 29

How do LEDs and lamps show the presence of current?

Answer 29

They only light up when a current is present. Therefore they indicate the presence of current.

Question 30

What is the equation for voltage?

Answer 30

Current X resistance.

Question 31

What is current?

Answer 31

The rate of flow of charge.

Question 32

What is the equation for charge

Answer 32

Charge= current X time.

Question 33

What is electric current?

Answer 33

The flow of negatively charged electrons.

Question 34

What is voltage?

Answer 34

The energy transferred per u it of charge. A volt is a joule per coulomb.

Question 35

What are metals and non metals described as ?

Answer 35

Metals are conductors (poor insulators) | Non metals are insulators (poor conductors)

Question 36

Describe an experiment to see how materials can be changed by friction.

Answer 36

1) take a polythene rod and rip up bits of paper. 2) hold a rod by the paper * nothing will happen as the rod has not been charged by friction* 1) rub the polythene rod with a cloth. 2) hold the rod by the bits of paper. 3) the paper will attract as the rod has lost electrons= positively charged. * this is because the paper is neutral, so protons are repealed away by the rod's charge*

Question 37

What is it called when materials rub against against each other and one gains electrons whilst the other loses electrons?

Answer 37

Electron transfer. The loss of electrons makes the object positively charged. The gain of electrons makes the object negatively charged.

Question 38

What charges attract each other and what charges repeal each other?

Answer 38

Opposite charges attract. | Alike charges repel.

Question 39

What is an electrostatic phenomena?

Answer 39

An event where static electricity has a specific effect e.g lightning. Electrons move from one material to another,and the material with a negative charge will look for a way to earth its charge.

Question 40

When an electrostatic charge builds up, it can create a spark. Name an example where this could happen and how it can be avoided.

Answer 40

When refuelling vehicles, the fuel rubbing against the walls of the pipe can cause an electrostatic charge to build up which can easily lead to a spark. This could ignite a fire or an explosion. This can be avoided if the nozzle so made of metal so that the charge is conducted away or by having earthing straps between the fuel tank and the pipe.

Question 41

How do inkjet printers use the idea of electrostatic charge?

Answer 41

Parts where you want the ink to land on are positively charged and the ink itself is given the opposite charge. This means that the ink is only attracted to parts where you want it to go.