Paper 1 Topic 2

Question 1

How does current flow in series + how to measure current

Answer 1

Current flows in one direction (same all way round in series)
Use an ammeter

Question 2

Current in parallel

Answer 2

Current in branches add up to total current leaving the cell

Question 3

How is PD measured

Answer 3

Voltmeter

Question 4

PD across lamps in series

Answer 4

PD across lamps is same as pd across cell

Question 5

PD in parallel

Answer 5

Pd across each component is the same

Question 6

What’s a battery

Answer 6

2 or more cells connected together

Question 7

PD in batteries

Answer 7

The cells in battery must be connected in same direction otherwise PD is 0

Question 8

What’s charge

Answer 8

Rate of flow of electrical charge

Question 9

What’s resistance tell us

Answer 9

Tells us PD required to drive a current through a current
PD/current

Question 10

What are resistors and why are they useful in circuits

Answer 10

Adds extra resistance (to make lamps dimmer)
Useful because PD is shared between lamp and resistor = less electrical energy transferred

Question 11

What’s current like in resistors

Answer 11

Directly proportional to PD = ohmic conductor
Only constant if temp is constant

Question 12

Resistance of a filament lamp

Answer 12

Not ohmic as filament gets hot atoms collide more with the electrons as they vibrate

Question 13

Diode current

Answer 13

Flows in one direction only
As diode has very high resistance in reverse direction

Question 14

LED current

Answer 14

Gives off light when current flows through

Question 15

Resistors in series + why

Answer 15

Add together - as currennt cannot bypass any resistor

Question 16

Resistors in parallel

Answer 16

Total resistance of 2 resistors is less than resistance of smallest Individual resistor

Question 17

What is the resistance like when conditions are light in LDRS

Answer 17

Low resistance as takes very little energy for current to pass through LDR = pd is low

Question 18

LDR dark conditions

Answer 18

Takes great deal of energy for current to pass through LDR so pd across LDR is high = less electrical energy available for lamp = dim

Question 19

If temps increases what happens to resistance of thermistors

Answer 19

Resistance decreases (useful as thermometers)

Question 20

Thermistors under cool condition (in a fan)

Answer 20

Resistance is high so lot of energy req to pass through thermistor so pd is high so pd across cooking fan is low cooperates at low speed

Question 21

Energy transfers for blender + fan

Answer 21

Electrical -> kinetic + thermal (wasted)

Question 22

Iron + kettle transfers

Answer 22

Electrical -> thermal

Question 23

Hair dryer + washing machine transfers

Answer 23

Electrical -> kinetic + thermal
appliances designed for thermal have higher power rating

Question 24

DC current

Answer 24

Current from a cell is DC (one direction)

Question 25

Why’s AC used in Uk
What is Hz and PD of AC in uk

Answer 25

Mains electricity in UK is AC because it’s easy to use transformer to increase or decrease pd
50Hz and 230V

Question 26

Live wire

Answer 26

Brown
Carries alternating PD
Connected to a fuse in plug

Question 27

Neutral wire

Answer 27

Blue
Completes circuit
0V

Question 28

Earth wire

Answer 28

Green / yellow
Safety wire
Stops appliance from becoming live

Question 29

Why can the live wire be dangerous in metal cases

Answer 29

Fatal if touched (electrocuted) so appliances with metal cases can be dangerous as if earth wire comes loose and touches case it becomes live wire)

Question 30

Why does earth wire stop live wires

Answer 30

Connected in the ground with metal rod
If case becomes live a huge current flows to earth
Fuse melts + shuts off current

Question 31

What’s the national grid

Answer 31

System of transformers and high voltage cables

Question 32

Step up transformers

Answer 32

Increase PD massively so less energy is lost to surroundings

Question 33

Step down transformers

Answer 33

Reduces PD to 230V so it’s safe to go into homes