P3

battery

a store of chemical energy (2 or more cells in series)

cell

a store of chemical energy

switch

turns on and off to break and reconnect a circuit

lamp

Lights when current flows

Fixed Resistor

Resistors that have a value that cannot be changed + limits the current in a circuit

variable resistor

can vary the size of the current

voltmeter

measures the potential difference

ammeter

measures the current

thermistor

temperature dependant resistor. low resistance in high temperatures

LDR

light dependant resistor. low resistance in high light intensity

diode

A device that permits current to flow through it in only one direction.
(very high resistance in one direction, low in the other direction)

current

A flow of charged particles

how to calculate charge

Q=It
charge = current x time

current in a series circuit

the same at every point

Current in a parallel circuit

split between loops

voltage in a series circuit

split between components

voltage in a parallel curcuit

same in every loop but split between components

electrical resistance

everything that resists or opposes the flow of electrons

ohms law

the current though a conductor between 2 points is directly proportional to the voltage across the 2 points
R = V/I

factors that affect resistance

temperature (ions in the metal vibrate faster making it for difficult for electrons to flow)
length
diameter

resistance in a series circuit

R total = R1 + R2

resistance in a parallel circuit

lower than the lowest resistor

why does a lamp not obey ohms law

as current flows, the metal fillament gets hotter so the atoms vibrate faster resulting in a higher collision frequency and increasing resistance
(shown by the flattening out of the graph)
​

power

amount of work done/energy transferred by unit time

how to calculate power

P = IV
power = current x voltage

P = 1² R

how to calculate electrical energy

E = Pt
energy = power x time

how can an object become statically charged

by rubbing 2 insulators together as there is a transfer of electrons on the surface

direct current

a flow of electric charge in only one direction

alternating current

A flow of electric charge that regularly reverses its direction.

an oscilloscope

used to display and measure a dc or ac wave form

earth wire

-yellow green
- goes straight up
-safety wire

neutral wire

-blue
-goes to left
-always at 0v

fuse

safety device
above live wire
melts and breaks the circuit when the current passing through gets too high

live wire

-brown
-goes to right
-alternates voltage between -325 and +325

how does the earth wire work

the earth wire is connected to the metal casing of the plug
if the casing becomes live the earth wire provides a low resistance path to draw current away
the large surge of current blows the fuse, breaking the circuit

static electricity

a build up of charge on an object (caused by the friction and transfer of electrons)

how can static electricity cause a spark

a large build up of charge on an object can cause a large potential difference between the object and the earth. the large P.D. could allow electrons to jump thru the air to earth, causing a spark

why dont conductors become static

as the electrons would just flow straight back again

potential difference

The force or strength of electron flow

charge

a measure of the total current that flowed within a period of time