IGCSE Edexcel physics electricity

current

amps (A)

Charge

Coulombs (C)

Energy

Joules (J)

Resistance

Ohm (Ω)

time

second (s)

Voltage

Volts (v)

Power

watt (W)

Series circuit rules current

Current is the same everywhere - ammeter readings are the same
Current depends on the applied voltage + the no and nature of other components

Series circuit rules voltage and general

Voltage is shared between components that are the same
Control all components with one switch
The more bulbs added the dimmer
Bulbs break - whole circuit does not work

Parallel circuit rules current

Current splits at each branch equally if the components are the same

Parallel circuit voltage and genera

Voltage is same as total voltage across each branch
Voltage across 2 components connected in parallel is the same
Can include a switch to control each branch independently of others
If one bulb breaks, others keep working
Every branch has the same voltage so brightness stays the same

Current/voltage filament shape

S shape
Resistant of a filament increases as the temperature of the filament increases
Reversing the voltage (negative values on graph) reverses the direction of the electric current but not the shape of the curve

Does the lamp obey ohms law?

No

Current voltage graph of a fixed resistor

Straight line through the origin

What is ohms law?

Current is proportional to the voltage

Does the wire or fixed resistor obey ohms law?

Yes

What does a diode do?

Current flow only flows through a diode in one direction
Has very high resistance in the reverse direction

What is resistance?

A measure of how hard it is for the current to flow
All devices have some resistance - a resistor is a device that has a particular resistance
Increasing the resistance will decrease the current you can do this by adding more components or ones with higher resistance

Resistance of thermistor

The resistance of a thermistor decreases as the temperature increases
The higher temperature line therefore has a greater slope than the lower temperature case

Resistance of light dependant resistor

The resistance of a light dependant resistor decreases as light intensity increases
The bright light line therefore has a greater slope than the dim light case

What is electric current

The rate of flow of electric charge

What can lamps and leds can be used to do?

Indicate the presence of a current in a circuit

What do metallic conductors do?

Copper wire electrons carry negative charge from the negative side of a power supply, around a circuit and back into the positive side

What happens in parallel circuits?

Total amount of current flowing into the junction or split is equal to the total current flowing out

Conductor

Material through which electric current flows easily

Insulator

Have a very high resistance to the flow of electric current

Examples of conductors

Copper
Steel
Graphite
Mercury

examples of insulators

Paper
Rubber
Plastic
Diamond

What happens when insulating materials are rubbed against each other?

They become electrically charged

What happens in term of electrons?

Electrons are rubbed off one material onto the other
The material that gains electrons becomes negatively charged
The material that loses electrons is left with an equal positive charge

What attracts and repel?

Forces of attraction between unlike charges
Forces of repulsion between like charges

What is electrostatic phenomena

When static electricity has an imbalance of electric charges in a material has a specific effect
Electrons move from one material to another

What do materials with a negative charge want to do?

Want to earth its charge

Uses of electrostatic charges

Photocopiers - light reflects off paper onto positively charged drum, black toner doesn't reflect so the drum keep its charge in these areas, black toner is pressed onto paper
Paint sprayers - as paint droplets leave they repel each other and spread out to form a fine cloud of paint, the negatively charged metal attracts the positively charged paint

Dangers of electrostatic charges

Refuelling aircrafts - if the fuel in the hose built up an electric charge, a spark might form and ignite the fuel (hoses earthed to prevent this)
Tankers - transporting liquid chemicals in ship tanks can build up static electricity causing a spark and igniting the liquid