1) Electrostatic charges involve the attraction and repulsion of objects based on whether they have equal or opposite charges. Charges are used in photocopiers, dust precipitators, and defibrillators. 2) Electricity involves the flow of electrons through conductors. The resistance of materials can change based on factors like temperature. Common circuit components include resistors, diodes, and capacitors. 3) Digital and analog signals are used to transmit information. Digital signals use 1s and 0s while analog signals have continuously varying values. Multiplexing and sampling allow more data to be transmitted.

1. Like charges repel, unlike attract.
resistance. = voltage / current The diode has a very high R in the reverse
Discharging is when a charged object is connected Ohmic conductors obey Ohm’s law where R is direction.
to earth. constant. Eg metal wire. Graph:
Friction removes electrons from insulators. Eg a The resistance of a filament lamp
increases as the temperature of
polythene rod becomes negative while the cloth
the filament increases so it
becomes positive. is non-ohmic. The R of a thermistor decreases as the
temperature increases.
The R of a light-dependent resistor (LDR)
Electrostatic charges are used in photocopiers to decreases as light intensity increases.
attract the toner ink,
in dust precipitators a positive grid gives the dust resistance
particles a positive charge so they are attracted to
the negative grid.
In computers we use digital signals consisting
In a defibrillator large paddles are charged up and
placed over your chest.
static of 1 (on) or 0 (off). Analogue signals have
In electrostatic paint sprayers the paint picks up electronic continuously varying values.
charge as it comes out and the particles repel each More information or data can be transmitted
other but get attracted to the oppositely charged communications using multiplexing – interleaving extra signals
object.
Electricity on the same line.
Also less interference from noise.
Aircraft need to be earthed when refuelling to Analogue signals from a microphone are
prevent the inflammable vapour from exploding. sampled 6400 times a second and coded into a
string of 8 ones or zeros. Eg 10110110.
mains supply A laser reads a DVD or CD which has a spiral
Logic gates of pits (0) or no pits (1).
The mains supply is alternating in direction at 50Hz.
The p.d. is about 230 V. for all the sockets in parallel
The output Vout of a potential divider (a resistor and a sensor in
Brown wire = live neutral = blue To change AC to DC we use a diode, which series) can be fed to a decision making logic gate.
Earth = green and yellow. only conducts in one direction, to give half- The output of an OR gate is high (1) when either input A or input
If the current exceeds the fuse rating, it will melt and wave rectification. B is high.
break, protecting the cable from overheating. A circuit
breaker is used in a fuse box.
The AND gate is high when input A
Metal casings are connected to the earth wire. Full-wave rectification can be got with a and input B are high.
Finding the cost: bridge circuit with 4 diodes.
Energy = power x time We can smooth the output by using a The NOT gate inverts the input. 1 becomes 0.
Kilowatt-hours = kW x hours capacitor, which will discharge its charge If an alarm system is activated it needs to stay on – we can use a
You will be told the cost of one kWh, usually about 8p when the voltage starts to drop. bistable latch circuit, which uses two NOR gates.