Fuses melts if the current gets too high to prevent a fire.
Circuit breakers again break the circuit if current is too high.
Insulation and double insulation prevent people from touching exposed wires and getting shocks.
Earthing provides a low resistance path to the earth.
Resistance causes transfer of electrical energy to heat energy (electrons collide).
P = IV
P: Power (W), I: Current (A), V: Potential Difference (V)
E = IVt
E: Energy (J), t: time (s).
Alternating current (ac): current constantly changing direction.
Direct current (dc): current only flows in one direction.
Components of a circuit: a cell or battery, filament lamp (bulb), ammeter in series, voltmeter in parallel, resistors.
Series Circult (tutormyself.com)
Series circuits: less wires (easier).
Parallel circuits: if one components, circuit still works, every bulb has the same voltage (brightness).
Series Circuits: (one loop). Current is the same everywhere. Voltage adds up to battery. Resistance adds up.
Parallel Circuits: Voltage is the same everywhere. Current adds up from each branch.
V = IR
R: Resistance (Ω)
Q = It
Q: Charge (C)
Since I = Q/t, current is the rate of flow of charge (a flow of negatively charged electrons).
E = QV
Conducting Materials: Aluminium, Copper, Silver, Golf. Will conduct electricity
Insulating Materials: Glass, Air, Plastic, Rubber, Wood. Will not conduct electricity.
Investigate how insulating materials can be charged using friction
Hold polythene rod and cloth next to small pieces of paper one at a time
Now rub the rod with the cloth
Again hold close to small pieces of paper, observe.
Turn on a tap so a thin stream of water is flowing
Hold the rod about 1cm away from the water just below the nozzle, observe
Repeat with different material rods and cloths.
Opposite charges attract and likecharges repel.
Positive charges are formed when electrons are lost.
Negative charges are formed when electrons are gained.
There are some potential dangers of electrostatic charges
e.g. when fuelling aircraft and tankers, be careful that the aircraft didn't get charged when flying. Earth the plane with a conductor as soon as it lands.
Useful inprinters: Paper is charged negatively in certain parts. Positively charged paint droplets are sprayed onto the paper and attracted to the negative for the image.
