Topic P2 - Electricity

Question 1

Current definition

Answer 1

Flow of electrical charge

Question 2

What is current measured in?

Answer 2

Ampere, A

Question 3

Potential difference definition

Answer 3

Driving force that pushed charge round

Question 4

What is potential difference measured in?

Answer 4

Volt, V

Question 5

Resistance definition

Answer 5

Anything that slows down charge flow

Question 6

What is resistance measured in?

Answer 6

Ohm, Ω

Question 7

Current through a component depends on two factors:

Answer 7

1)
The component’s resistance

• The greater the resistance, the smaller the current.

2)
The potential difference across the component.

• The greater the potential difference, the larger the current (for a fixed resistance).

Question 8

Size of current = rate of…

Answer 8

Size of current = rate of flow of charge

Question 9

Charge flow formula

Answer 9

Q = It

Q - charge flow (C)
I - current (A)
t - time (s)

Question 10

What is charge flow measured in?

Answer 10

Coulombs, C

Question 11

Potential difference equation

Answer 11

V = IR

V - Potential Difference (V)
I - Current (A)
R - Resistance (Ω)

Question 12

For circuit symbols look at page 83.

Answer 12

For circuit symbols look at page 83.

Question 13

What are the 3 different I-V characteristics?

Answer 13

1) Ohmic conductors at constant temperature
2) Filament Lamp
3) Diode

Question 14

I-V ohmic conductor at constant temperature graph characteristics

Answer 14

Current is directly proportional to potential difference so resistance doesn’t change.

Question 15

Current is directly proportional to potential difference…

Answer 15

…so resistance doesn’t change

Question 16

Is an ohmic conductor I-V graph liner or non-linear?

Answer 16

Linear

Question 17

What are 4 examples of components with changing resistances when the current through them varies?

Answer 17

1) Filament Lamp
2) Diode
3) LDR
4) Thermistor

Question 18

I-V, filament lamp graph characteristics

Answer 18

Current increase so temperature of filament increases so resistance increases.

Question 19

I-V, diode graph characteristics.

Answer 19

High resistance in one direction so current only flows in the other direction.

Question 20

Are filament lamps and diode graphs linear or non-linear.

Answer 20

Non-linear

Question 21

An LDR resistance depends on?

Answer 21

Light intensity

Question 22

An LDR has lower resistance in?

Answer 22

Brighter light

Question 23

LDRs are used in?

Answer 23

Automatic night lights

Question 24

A thermistors resistance depends on?

Answer 24

Temperature

Question 25

A thermistors has lower resistance in?

Answer 25

Hotter temperatures

Question 26

Thermistors are used in?

Answer 26

Thermostats

Question 27

What are the 2 types of electricity supply?

Answer 27

1) Alternating current | 2) Direct Current

Question 28

Alternating current (ac) definition

Answer 28

Current that constantly changes direction and is produced by an alternating voltage. Used in mains supply.

Question 29

Direct Current (dc) definition

Answer 29

Current that always flows in the same direction and is produced by a direct voltage. Supplied by batteries.

Question 30

When charge flows, work is done and so…

Answer 30

When charge flows, work is done and so energy is transferred

Question 31

How is energy transferred from a plug socket to a kettle?

Answer 31

Energy is transferred electrically, to thermal energy store of the heating element inside the kettle.

Question 32

How is energy transferred from a battery to a fan?

Answer 32

Energy is transferred electrically, the the kinetic energy store of the fan’s motor.

Question 33

Energy transfer formulas

Answer 33

E = QV E = Pt ``` E - energy transferred ( J ) Q - charge flow (C) V - Potential Difference (V) P - power (W) t - time (s) ```

Question 34

Amount of energy an appliance transfers depends on:

Answer 34

- appliance’s power | - how long appliance is on for

Question 35

Power definition

Answer 35

Energy transferred per second

Question 36

Power rating definition

Answer 36

Maximum safe power an appliance can operate at.

Question 37

Power formulas

Answer 37

P = VI P = I²R P - power (W) V - potential difference (V) I - current (A) R - resistance (Ω)

Question 38

National grid definition

Answer 38

A system of cable and transformers that connect power stations to consumers

Question 39

What does a step-up transformer do?

Answer 39

Increases potential difference

Question 40

What does a step-down transformer do?

Answer 40

Decreases potential difference

Question 41

How can electrical power be transferred efficiently?

Answer 41

High potential difference and a low current.

Question 42

What would happen if electrical power was transferred at a high current?

Answer 42

Wires would heat up and transfer a lot of energy to the thermal energy stores of the surroundings.

Question 43

Density formula

Answer 43

p = m/v p - density (kg/m³) m - mass (kg) v - volume (m³)

Question 44

What is density’s unit?

Answer 44

kg/m³

Question 45

What can increased internal energy of a system do?

Answer 45

1) Increase temperature | 2) Change in state

Question 46

The higher the temperature of a gas, the higher the average energy…

Answer 46

In the kinetic energy stores of the gas particles

Question 47

Gas pressure is caused by…

Answer 47

Gas particles colliding with a surface and exerting a net force on it.

Question 48

If a gas at a constant volume has a temperature increase what will happen?

Answer 48

Gas particles get faster and collide with the container more often, leading to a pressure increase