P2 electricity Flashcards
Static electricity
Insulators cause a build up of charge. When it flows to a conductors you get a shock.
Charged by friction
Electron transfer
An atom consists of a small positively charged nucleus surrounded by negativity charged electrons. In a neutral atom direct equal numbers of positive and negative charges. All electrostatic effects are caused by the movement of electrons
Electric field
A region where a force acts on a charged particle
Field
A region of space where a force can act at a distance
Strength of an electric field
The closer to the centre the stronger it is
Sparking
Air is an electrical insulator not conductor
However when there are very strong electric field the atoms and molecules in the air break apart to form positive and negative ions
Charged ions experience force from the field and move
Creating a spark
Electric current
The rate of flow of electric charge from negative to positive
Electric charge
Is measured in coulombs
Potential difference
The energy transferred per unit charge as charges move between 2 points in a circuit. It is measured in volts using a voltmeter which is always connected in parallel
Resistance
Electrons collide with metal ions in the resistor
Energy transferred to metal ions so vibrate and resistor gets hotter
Increased vibrations of ions in fixed lattice makes it harder for electrons to travel through so resistance increases
Series circuit
Components connected next to each other in a single loop
Lamps shine duller
Parallel circuit
Components are connected to each other like rungs in a ladder
Lamps shine brighter
Resistors in series
R1 and R2 has the same current as the current has to pass through both of them
Total resistance is R1+R2
Have same pd that combined is the of of battery
Resistors increase total resistance
Resistors in parallel
Current can either pass through R1 or R2 meaning the ammeter reading is A1 equal to the sum of A2+A3
Pd of battery is the same as pd across each component
V1+V2 are the same and = of of battery
Resistors decrease total resistance
Parallel calculations
Pd is identical across each resistor
Current is sum of currents that pass through each resistors
Series calculations
Pd is sum of all pd across resistors
Current is same through all resistors
Measuring resistance of resistor
Battery,variable resistor,resistor,voltmeter, ammeter
Straight line through origin, ohmic conductor
Measuring resistance of filament lamp
Battery,variable resistor,resistor,voltmeter, ammeter
Upside down curve non ohmic conductor
Required practical – investigate, using circuit diagrams to construct circuits, the IV characteristics of a filament lamp,a diode and a resistor at constant temperature
2 variables-pd and current
0-12 V dc, voltmeter,component,ammeter and variable resistor
Resistor is ohmic (straight line)
Filament lamp isn’t ohmic (s shape)
Diode isn’t ohmic (straight line then increases)
Required practical – use circuit diagrams to set up and check appropriate circuits to investigate the factors affecting the resistance of electrical circuits, including the Length of a wire at a constant temperature and combinations of resistors in series and parallel
0-12 V dc battery, component, voltmeter, ammeter and variable resistor Find pd & current of each length Plot on a graph Do this in series by adding component For parallel Add components in parallel
Sensors
Detect changes in the circuit
Thermistor
A light dependant resistor. Resistance changes a lot as temperature changes
Low temp= high resistance
High temp= low resistance
2000 ohms at -20 degrees
200 ohms at 20 degrees
Made from a semi conductor (not insulator or conductor)
Light dependant resistor
LDR
Resistance changes a lot as light intensity changes
Bright= resistance low
Dark= resistance high
Uses of thermistors
Turn on heating when it gets cold
Fire alarm
Stop fish tank getting too cold
Uses of LDRs
Simple light meter
Used in cricket to see if it is too dark to play or not
Diode
Only allows current to flow in one direction. The direction the arrow points to
Most start to conduct pd at 0.6V
A cell has 2 terminals
Positive and negative
Current is dc (Always passes in same direction)
Mains electricity differs in 2 ways
Current alternates at a frequency of 50Hz
It has a much higher potential difference 230 V
Live wire
Brown wire
Connect to house
Carries high pd into and around the house
Fuse in plug is always connected to live wire
Neutral wire
Blue wire
Return path to local sub station
Is earthed so close to earth potential
No current in wire till electrical appliance is connected
Earth wire
Yellow/green striped wire Safety wire Connected to wire case of an appliance to prevent it being charged of touched by live wire Low resistance path to ground Normally no current in it
National grid
A collection of power cables and transformers that connect power stations to factories and houses across Britain
Changing the pd
Domestic uk mains supply 230V
Electrical power is transmitted across the country at 400000V
Pd between live and earth is very big
The higher the pd the lower the current
The lower the current the less energy lost as heat
Transformers
Devices that can change the pd
Made with 2 coils of wire with some iron passing between them
Varying number of turns on coil changes pd
Step up transformers
Increase pd
Connected between power stations and the national grid
Step down transformers
Decrease pd
Power
The amount of energy transferred each second
When charge flows in a circuit
Electrical work is done
Power transfer
Potential difference across it and the current passing through it
Current
A flow of charge
Potential difference
Work done by moving a unit of charge
Energy transferred
Resistance
How hard the current is being opposed
