Electricity

Question 1

What are amperes (A)?

Answer 1

Unit for current (coulombs per second)

Question 2

What are coulombs (C)?

Answer 2

Unit for charge

1C = 6.25 * 10 to the 18 electrons

Question 3

What are joules (J)?

Answer 3

Unit for energy

Question 4

What are ohms (Ω)?

Answer 4

Unit for resistance of a component

Question 5

What are volts (V)?

Answer 5

Unit for voltage (potential difference)

1V = 1J/C (joule per coulomb)

Question 6

What are watts (W)?

Answer 6

Unit for power (joules per second)

Question 7

What is insulation?

Answer 7

When wires are covered by rubber, an insulator.

Question 8

What is double insulation?

Answer 8

Appliances that have plastic cases without any wires connected to the case, so that the case cannot become live as it is an insulator.

Question 9

What is earthing?

Answer 9

Earth wires create an escape route for current to flow through if the appliance develops a fault.
If the live wire becomes loose and touches the metal case, a very large current flows through the earth wire, blowing the fuse and creaking the circuit.

Question 10

What are fuses?

Answer 10

A very thin wire, which melts if the current is too high, breaking the circuit.
Rating in amps tells you the maximum current that can go through.

Question 11

What are circuit breakers?

Answer 11

An automatic electromagnet switch which breaks the circuit if the current rises over a certain value.
Better than a fuse as it is more sensitive and can be reset.

Question 12

What do resistors do?

Answer 12

When current flows through, the resistor heats up as electrical energy is transferred to thermal energy. This makes the metal ions vibrate more, making it harder for electrons to find a clear path through.

Question 13

Relationship between power, current and voltage:

Answer 13

power = current x voltage
P = IV

Question 14

Relationship between energy transferred, current, voltage and time:

Answer 14

energy transferred = voltage x current x time

E = VIt

Question 15

What is the mains electricity supply in the UK?

Answer 15

230V

Question 16

Relationship between voltage, current and resistance:

Answer 16

voltage = current x resistance
V = IR

Question 17

Is mains electricity AC or DC?

Answer 17

AC supply (alternating current)

Question 18

Are cells/batteries AC or DC?

Answer 18

DC supply (direct current)

Question 19

Properties of a series circuit

Answer 19

Current is the same everywhere
Voltage/potential difference is shared between components
Total resistance is the sum of the resistance of each component

Question 20

Properties of a parallel circuit

Answer 20

Current is split between branches
Voltage/potential difference is the same on every branch, shared between components on each branch
1/R = 1/R1 + 1/R2

Question 21

What is voltage/potential difference?

Answer 21

Energy transferred per unit charge

Measured in volts

Question 22

How does current change as you change the voltage with a wire?

Answer 22

As you increase the voltage, the current increases

Directly proportional

Question 23

How does current change as you change the voltage with a resistor?

Answer 23

As you increase the voltage, the current increases
Directly proportional
Steeper gradient is higher resistance

Question 24

Relationship between energy transferred, charge and voltage:

Answer 24

Energy transferred = charge x voltage

E = Q x V

Question 25

How does current and resistance change as you change the voltage with a filament lamp?

Answer 25

As the voltage increases, the current rapidly increases
As the temperature increases, the resistance (gradient) increases, hence the curve
Curve getting shallower

Question 26

How does current change as you change the voltage with a diode?

Answer 26

Current only flows in one direction (current only increases in first quadrant)

Question 27

How does changing resistance affect current?

Answer 27

As resistance increases, current decreases (inversely proportional)

Question 28

What do LDRs (light dependant resistors) do?

Answer 28

As light intensity increases, they decrease the resistance.

Question 29

What do thermistors do?

Answer 29

As the temperature increases, they decrease the resistance.

Question 30

What are LEDs (light-emitting diodes)?

Answer 30

Emit light when current flows through

Don’t have a filament so cannot burn out

Question 31

What is resistance?

Answer 31

How difficult it is for charge to flow through something
Measured in ohms (Ω)
Insulators have high resistance, conductors have low resistance

Question 32

What does Ohm’s Law state?

Answer 32

Voltage is directly proportional to current when temperature is constant
V∝I

Question 33

What is the standard frequency in the UK?

Answer 33

50Hz

Question 34

What is current?

Answer 34

Rate of flow of charge
Measured in amps (coulombs per second)
Flow of negatively charged electrons

Question 35

Relationship between charge, current and time:

Answer 35

charge = current x time
Q = I x t

Question 36

Examples of electrical conductors:

Answer 36

All metals

Question 37

Examples of electrical insulators:

Answer 37

Plastic, wood

Question 38

What is static electricity?

Answer 38

The build-up of electric charge on an insulated object.

Question 39

Rubbing polythene and acetate rods with a cloth

Answer 39

Electrons move from the duster to the polythene rod, making the duster +ve and the rod -ve
Electrons move from the acetate rod to the duster, making the rod +ve and the duster -ve.

Question 40

Using a gold-leaf electroscope

Answer 40

Bring the charged object to the disc of the electroscope
This induces a charge in the metal disc, which induces a charge in the gold leaves
As the gold leaves have the same charge, they will repel eachother.

Question 41

How does an inkjet printer work:

Answer 41

Uses charged plates to direct a spot of ink onto the pager