Electricity

Question 1

What is electric current?

Answer 1

Flow of electrical charge

Question 2

What can be said about the value of current at any point in a SINGLE CLOSED LOOP?

Answer 2

Current is the SAME at ALL points in a CLOSED loop

Question 3

What 2 factors does current in a circuit depend on

Answer 3

• Potential Difference
• Resistance

Question 4

What is an Ohmic Conductor?>

Answer 4

• Conductor where CURRENT and PD are Directly Proportional
• Resistance remains constant
• Temp must be constant

Question 5

List 4 components where resistance is not constant as current changes

Answer 5

• Lamps
• Diodes
• Thermistors
• LDRs

Question 6

What happens to resistance of filament lamp when temp increases?

Answer 6

• Resistance increases
• Ions in metals have more energy, so vibrate more
• More collisions with electrons as they flow thru metal
• Which creates greater resistance to current

Question 7

What is different about current flow through a diode?

Answer 7

• Current only flows in 1 direction
• Resistance is very high in other

This prevents CURRENT FLOW

Question 8

what happens to Resistance of a THERMISTOR as TEMP increases?

Answer 8

Thermistor’s resistance decreases

Question 9

2 examples where thermistors are used?

Answer 9

• In THERMOSTAT to turn HEATER on below certain temp
• In FREEZER to turn COOLER on when temp becomes too HIGH

Question 10

What happens to resistance of LDR as light intensity decreases?

Answer 10

LDR resistance increases

Question 11

Give one application for LDR

Answer 11

• Street lights

Question 12

What supply is Mains electricity?

Answer 12

AC

Question 13

what frequency does DOMESTIC ELEC SUPPLY in the UK have?

Answer 13

50hz

Question 14

how many volts is uk domestic

Answer 14

230V

Question 15

How many wires are there in a plug?

Answer 15

3 - Live, Neutral, Earth

Question 16

Describe the Live Wire?

Answer 16

• Brown
• 230 V
• Carries AC from supply
• Hazardous as current continually flowing

Question 17

Describe neutral wire

Answer 17

• Blue
• 0 V
• Completes circuit

Question 18

Describe earth wire

Answer 18

• Yellow green, 0 V
• Safety wire to stop appliance going live
• Connected to earth and casing
• If Live wire touches metal casing, it will become live and you can get shocked

Question 19

What is power?

Answer 19

Energy transferred per second.

Directly proportional to current and voltage

Question 20

What is power loss?

Answer 20

• Proportional to resistance
• Proportional to square of current

Question 21

What is the National Grid?

Answer 21

System of cables and transformers linking power stations to consumers across UK

Question 22

What is a transformer?

Answer 22

Changes P.D

Question 23

Do insulators conduct?

Answer 23

No

Electrons cannot flow throughout material, they are fixed

Question 24

Can conductors conduct?

Answer 24

Yes
Electrons can flow, because they are DELOCALISED

Question 25

What is static electricity?

Answer 25

Build up of charge on insulating materials

Question 26

Why do objects normally have a neutral charge overall?

Answer 26

Because the protons and electrons cancel out

Question 27

How does static electricity build up?

Answer 27

2 objects rubbed together
- Friction causes electrons to move from one object to other

• Leads to build up of charge

Question 28

Is static electricity more likely to build up on conductors or insulators?

Answer 28

More likely on insulators, because electrons will flow back if material was conductor

Question 29

What causes a spark between object and earth?

Answer 29

Large build up of charge can cause large P.D

Large P.D allows electrons to jump to other object

Question 30

What is a fuse?

Answer 30

Thin piece of wire between live wire. If surge happens, fuse will melt as a failsafe.