Static electricity
Same charges repel and unlike charges attract
When rubbing two insulating material together they get electrically charged.
Only works for insulators as in metals the charge is earthed too easily.
Electrons move from one material to the other when rubbed against each other
The material that lost electrons become positively charged
The one that gained electrons become negatively charged.
Charge are equal but opposite.
Charged objects will repel or attract
Same charge repel
Different charge attract.
A charged object may also attract uncharged objects.
Circuit
Circuit diagrams must always be complete without any short circuits for it to work.
Wire should lead from battery to the battery.
Short circuit, electricity takes the path of least resistance, if there is a path without any components there is a short circuit.
Current
In a series circuit current is the same
In a parallel circuit, current is shared
Current is measured in Amps (A)
Measured using an ammeter in series.
I= Q / t
Current = Charge /time
Amps (A) Coulombs (C) Seconds (s)
Voltage
Potential Difference is needed to make a current flow through it.
Measured in Volts (V)
Measured using a voltmeter must be connected in parallel with the component.
V= W / Q
Voltage = Work Done / Charge
Volt (V) Joules (J) Coulombs (C)
As Voltage increases the Current increases as well.
Voltage is shared in a series circuit in each component
Resistance
Resistance increases as length of wire increases or thickness of wire decreases.
Electrons move through a conductor for an electric current.
Moving electrons collide with ions in the metal causing resistance.
With a longer wire there are more collisions so resistance increases.
Thinner Wires has fewer electrons to carry current.
V= I * R
R = V / I
Voltage = Current / Resistance
Volts (V) Amps (A) Ohms (Ω)
Current flowing through a resistor at a constant temperature is directly proportional to the voltage.
Filament lamps produce light as the filament (think coil of wire) heats up. The resistance of the lamp increases.
LEDs
Diodes have a very high resistance on one side so current can only travel
the other way
LED produces light when a current travels through it, it is far more efficient than other light components it uses a much smaller current
thermistor is a variable resistor.
Its resistance decreases as its temperature increases.
LDRs are variable resistors that depends on the light intensity
The resistance increases as light intensity decreases.
Direct and Alternating current
If current flows in one direction it is called direct current (DC).
Batteries and cells supply DC usually around 1.5 V
Alternating current constantly changes direction.
Mains electricity is AC supplying 230V in the UK with a frequency of 50Hertz (Hz)
Cables
A mains electricity cable has 2 or 3 inner wires with cores of copper as copper is a good conductor of electricity.
The outer layer is made from plastic as it is a good insulator.
There is a colour code
Blue -Neutral
Brown -Live
Green and yellow stripes -Earth
The Plug
The plug is made from tough plastic which is a good insulator.
The 3 pins are made from brass which are stronger than copper and a good conductor of electricity
There is a fuse between the live fuse and terminal which breaks if there is too much current going through it.
The Cable grip grips the cable to stop it moving around.
bLue goes Left
bRown goes Right
sTriped Goes Top.
Fuses
Used to protect appliances.
The fuse breaks if there is too much current flowing through it. This protects the appliance if something goes wrong.
It has a wire that melts easily and it heats up and breaks if the current is too great.
The fuse rating is slightly higher than the device's current need
Standard ratings are 3A 5A and 13A.
Circuit Breakers
Circuit breakers detect a difference in current, they act like fuses but can be used more than once and act a lot faster.
However, they are more expensive.
Earthing
The earth wire creates a safe route for current to flow if the live wire touches a metal casing.
The earth wire has a low resistance so it stops current from flowing through our body.
As the strong current goes to the earth wire, it breaks the fuse.
Double insulation
Plastic casings doesn't require a earth wire as it is an insulator
Oscilloscopes
Periods- Time taken for an AC supply for one complete oscillation. One peak to the next
Frequency
Number of oscillations per second.
Frequency = 1 / period
Power
P= E/ t
Power = Energy / time
Watt (W) Joules (J) Seconds (s)
In a circuit,
P= I*V
Power (W) = Current (A) * Voltage (V)
E =V*Q
Energy (J) = Voltage (V) * Charge (C)
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