(2) Electricity

Question 1

Understand how the use of insulation, double insulation, earthing, fuses and circuits breakers protects the device or user

Answer 1

Insulation
* Putting a material that does not conduct electricity around a live conductor to stop the charges from escaping the wire whilst travelling through the circuit. It needs an earth wire due to the risk of the coating getting damaged a leaking charges.

Double insulation
* The appliance has a coating of plastic which lets the charges dissipate of it as plastic is an insulator. It also prevents people getting electrocuted. They don’t need earth wires.

Earthing
* If the live wire get disconnected from the appliance and gives the charge to outer metal casing the earth wire provides the path for the charges to travel down quickly as it has a low resistance to protect anyone from getting electrocuted and stop it from being dangerous. It directs the charge to earth.

Fuses and circuit breakers
* The fuse blows if the current of the live wire gets to high above the appliances working current to stop anything bad happening.

Question 2

Understand why a current in a resistor results in the electrical transfer of energy and an increase in temperature, and how this can be used in a variety of domestic
contexts

Answer 2

As current increases, electrons (charge) has more energy When electrons flow through a resistor, they collide with the atoms in the resistor This transfers energy to the atoms, causing them to vibrate more This makes it more difficult for electrons to flow through the resistor So resistance increases, and current decreases

As electric current flows through a resistor, some of the electrical energy is converted into heat energy. This causes the resistor to heat up. This heating effect occurs due to the metallic structure of the wire in the resistor.

E.g. electric heaters, ovens, toasters

Question 3

Know and use the relationship between power, current and voltage

Answer 3

power = current x voltage
p = I x V

And apply the relationship to the selection of appropriate fuses

Question 4

Use the relationship between energy transferred, current, voltage and time

Answer 4

energy transferred = current x voltage x time
E = I x V x t

Question 5

know the difference between mains electricity being alternating current (a.c.) and
direct current (d.c.) being supplied by a cell or battery

Answer 5

a.c
* The current goes back and forth, changing directly periodically.

d.c
* The current goes round the circuit in one constant direction.

Question 6

Explain why a series or parallel circuit is more appropriate for particular applications,
including domestic lighting

Answer 6

Examples
Lamp
* Series is more appropiate as the lamp is the only component in the circuit.

House lights
* A parallel ciruit would be better as you would be able to choose which lights should be on. If it was a series circuit you would only be able to have all lights on all none.

Question 7

Understand how the current in a series circuit depends on the applied voltage and the
number and nature of other components

Answer 7

If the voltage is increased, the current also increases. The more components in the circuit means the lower the current will be.
Its just I = V/R

Question 8

Describe how current varies with voltage in wires, resistors, metal filament lamps and
diodes, and how to investigate this experimentally

Answer 8

Directly Proportional
1. Wires
2. Resistor
Not directly proportional
1. Metal filament lamps
2. Diodes
Exampls of Metals filament lamp
* As voltage increases across the filament, the current also increases.
* The increase in current causes the temperature of the filament to rise.
* Higher temperature leads to an increase in resistance within the filament.
* Meaning the increased resistance slows the flow of charge, meaning the current increases slower.

Question 9

Describe the qualitative effect of changing resistance on the current in a circuit

Answer 9

The bigger the resistance the smaller the current in a circuit likewise for the other way round.

Question 10

Describe the qualitative variation of resistance of light-dependent resistors (LDRs)
with illumination and thermistors with temperature

Answer 10

Light-dependent resistors
* The more illumination/light the less resistance there is.
Thermistors
* The higher the temperature the less resistance there is.

Question 11

Know that lamps and LEDs can be used to indicate the presence of a current in a
circuit

Answer 11

They light up if there is a current present

Question 12

Know and use the relationship between voltage, current and resistance

Answer 12

voltage = current x resistance
V = I x R

Question 13

Know what current is

Answer 13

Current is the rate of flow of charge

Question 14

Know and use the relationship between charge, current and time

Answer 14

charge = current x tim
Q = I x t

Question 15

Know what electric current in solid metallic conductors are

Answer 15

A flow of negatively charged
electrons

Question 16

Understand why current is conserved at a junction in a circuit

Answer 16

Since current is the rate of flow of charge, whatever current flows into a junction is the same as the current flowing out of it.

Question 17

Know that the voltage across two components connected in parallel is the same

Answer 17

In parallel, each branch gets the full amount of voltage from the supply

Question 18

Calculate the currents, voltages and resistances of two resistive components
connected in a series circuit

Answer 18

Yep, check just incase with past papers

Question 19

Voltage

Answer 19

The energy transferred per unit charge passed

Question 20

Volt

Answer 20

A joule per coulomb

Question 21

Know and use the relationship between energy transferred, charge and voltage

Answer 21

energy transferred = charge x voltage
E = Q x V

Question 22

Identify common materials that are electrical conductors or insulators,
including metals and plastics

Answer 22

Electrical conductors
1. Copper
2. Iron
3. Steel
Insulators
1. Plastic
2. Wood
3. Glass
4. Rubber

Question 23

practical:

Investigate how insulating materials can be charged by friction

Answer 23

Rub cloth on a ruler and the cloths electrons arer transferred to the ruler causing the ruler to have a negative charge and the cloth to have an equal positive charge.

Note:
Protons dont move onto different objects only electrons.

Question 24

Explain how positive and negative electrostatic charges are produced on
materials by the loss and gain of electrons

Answer 24

Positive charges are produced when the object losses its electrons causing it to have an overall positive charge due to haveing more protons than electrons.
Negative charges are produced when the object gains electrons meaning there is more electrons than protons resulting in it have an overall negative charge.

Question 25

Know the forces of attraction

Answer 25

Attraction between unlike charges and forces of repulsion between like charges

Question 26

Explain electrostatic phenomena in terms of the movement of electrons

Answer 26

Is it the movement of electrons by processes like friction. A balloon rubbing agaisnt a jumper to become positively charged by its electrons rubbing of onto the jumper.

Question 27

Explain the potential dangers of electrostatic charges, e.g. when fuelling
aircraft and tankers

Answer 27

Fuelling tankers
* When fuelling tankers, the charges received by the tires (from their friction between the ground) would discharge down the wire to be grounded. This quick discharge of static electricity can cause a spark which could ignite the fuel in the tanker.

Fuelling aircrafts
* Charges collected by the plane at high altitudes or by storms can ignite when refuelling due to the quick discharge of static electricity. This could even lead to an explosion. The electric charges can also interfere with radio communications.

Question 28

Explain some uses of electrostatic charges, e.g. in photocopiers and inkjet
printers

Answer 28

Inkjet printers
* Each spot 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. The charges on the plates change hundreds of times each second so that each drop falls in a different position, forming pictures and words on the paper as required.

Photocopiers
1. The turning drum is charged
2. Image of the object to be copied is formed where it is charged. Charge only stays where image is dark.
3. Toner drops on to drum and sticks to charged areas.
4. Surplus toner is removed.
5. Paper is pressed against toner image to give the image on the paper.
6. Paper is heated to melt toner image. This forms permanent image on paper.