P3 - Electricity

Series circuits

• different components connected in a line end to end
• connecting several cells in series, all the same way (+ to -) gives a bigger total p.d. because each charge in the circuit passes through each cell and gets a 'push' from each one.
• Two 1.5V cells in series would supply 3V in total.
• Total potential difference is shared between the various components - so the p,d across the components always add up to equal the p.d. over the power supply  V=V1 + V2 
• Current is the same everywhere
• Resistance adds up

Parallel circuits

• Each branch is separately connected to the positve and negative terminals of the supply
• In parallel you can switch everything on and off separately
• Connecting cells in parallel does not increase the p.d. as each charge will only get a push from one of the cells
• P.d is the same across all branches
• Current is shared between branches
• Resistance - decreases as you add resistors (look up more)

Current: Rate of flow of electric charge

Voltage: How much push/energy the electricity has. 

                    Current     Voltage 

Series            Same      Split

Parallel          Split        Same

Resistance: Opposes the flow of charge

All metals have free electrons and will therefore conduct. The electrons do not have a free path, they are held back by the metal ions. We call this resistance.

OHMS Law:

V = I x R

Voltage = current x resistance

1) Type of metal 

2) Thickness of wire

3) Length of Wire

4) Temperature of wire

Independent variable: length of the wire

Depenant variable: Resistance

Control Variable: Thickness, temperature, type of metal

To calculate resistance we need current and amps so measue both (do this 3 times for each length) and change the length of the wire each time.

Power = current x voltage

P = I x V

Current - the movement of electrons through a wire

Thermistor: Resistance decreases with temperature.

LDR: Resistance decreases with light

Charge is the amount of electricity

Q = I x t

All devices transfer energy - their power is how quickly they do it

energy transferred (work done) = charge x potential difference

Power = energy/time

Power = p.d x I (voltage x current)

Power = I^2 x resistance

Magnetic Fields: Area around a magnet where you can feel the effects.

When current flows through a wire a magnetic field is created around it. The strenght of the magnetic field changes with the current and the distance from the wire. The larger the current through the wire or the closer you are to the wire, the stronger the field is.

You can increase the strength by of the magnetic field by:

• Wrapping the wire into coil called a SOLENIOD. The strength increases because the turns of wire line up together (and so add together). The magnetic effect of the sonlenoid can be increased by increasing the current, increasing the number of turns (with the same length) and deacreasing the cross-sectional area of the solenoid.
• Having a soft iron core in the middle of the coil causes it to become an induced magnet whenever the current is flowing, so the magnetic effect of the solenoid is increased.
• Increase the voltage - which increases the current.

• Transformers change the size of voltage of an alternating current.
• All have two coils of wire, the primary and the secondary, joined with an iron core
• When an alternating current is applied through the primary coil, it creates an alternating magnetic field