Electricity Flashcards
Topic 2, Paper 1
What is electric current?
Flow of electrical charge
What can be said about the value of current at any point in a SINGLE CLOSED LOOP?
Current is the SAME at ALL points in a CLOSED loop
What 2 factors does current in a circuit depend on
- Potential Difference
- Resistance
What is an Ohmic Conductor?>
- Conductor where CURRENT and PD are Directly Proportional
- Resistance remains constant
- Temp must be constant
List 4 components where resistance is not constant as current changes
- Lamps
- Diodes
- Thermistors
- LDRs
What happens to resistance of filament lamp when temp increases?
- 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
What is different about current flow through a diode?
- Current only flows in 1 direction
- Resistance is very high in other
This prevents CURRENT FLOW
what happens to Resistance of a THERMISTOR as TEMP increases?
Thermistor’s resistance decreases
2 examples where thermistors are used?
- In THERMOSTAT to turn HEATER on below certain temp
- In FREEZER to turn COOLER on when temp becomes too HIGH
What happens to resistance of LDR as light intensity decreases?
LDR resistance increases
Give one application for LDR
- Street lights
What supply is Mains electricity?
AC
what frequency does DOMESTIC ELEC SUPPLY in the UK have?
50hz
how many volts is uk domestic
230V
How many wires are there in a plug?
3 - Live, Neutral, Earth
Describe the Live Wire?
- Brown
- 230 V
- Carries AC from supply
- Hazardous as current continually flowing
Describe neutral wire
- Blue
- 0 V
- Completes circuit
Describe earth wire
- 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
What is power?
Energy transferred per second.
Directly proportional to current and voltage
What is power loss?
- Proportional to resistance
- Proportional to square of current
What is the National Grid?
System of cables and transformers linking power stations to consumers across UK
What is a transformer?
Changes P.D
Do insulators conduct?
No
Electrons cannot flow throughout material, they are fixed
Can conductors conduct?
Yes
Electrons can flow, because they are DELOCALISED
What is static electricity?
Build up of charge on insulating materials
Why do objects normally have a neutral charge overall?
Because the protons and electrons cancel out
How does static electricity build up?
2 objects rubbed together
- Friction causes electrons to move from one object to other
- Leads to build up of charge
Is static electricity more likely to build up on conductors or insulators?
More likely on insulators, because electrons will flow back if material was conductor
What causes a spark between object and earth?
Large build up of charge can cause large P.D
Large P.D allows electrons to jump to other object
What is a fuse?
Thin piece of wire between live wire. If surge happens, fuse will melt as a failsafe.
