Physics Module 2

What you need to learn Circuit symbols Measuring current and voltage in series and parallel circuits Current/Voltage graphs for certain components Resistance/Current/Voltage relationship Mains electricity Rate of energy transfer

Can you name these circuit symbols?

…and these?

…what about these?

Exam point Learn these symbols – you will definitely have to identify some symbols on the exam and you don’t want to lose simple marks.

Current What is current? What is the unit of measurement for Current? What do we use to measure current? Is current the same in series and parallel circuits?

What is current? Current is a flow of electrons (negative charges) around a circuit. The electrons carry the electrical energy needed to make things work

Units of measurement Current is measured in Amperes or Amps. The unit of measurement is ‘A’ Don’t forget this in the exam.

How do we measure current? We use an ammeter to measure current. This must be connected in series with the component you wish to measure. Don’t forget the symbol.

Summary for Series Circuits. 1.In a series circuit the current is the same at any point in the circuit. 2. The supply voltage is shared between the components in a series circuit. 3. The current depends on the voltage in ANY circuit.

Current/Voltage graphs This is identified by a straight line graph through the origin. The graph obeys Ohms law – current is directly proportional to voltage

Current/Voltage graphs This is identified by a curved graph It obeys ohms law at the start The curve shows that current does not increase even though the voltage does

Current/Voltage graphs A diode does not let current flow in reverse. It has a very high resistance when the current is reversed and so will not let it flow.

The relationship between current, voltage and resistance

V = IR The letter ‘I’ is used to represent current. Do not get it confused with the unit of measurement for current which is ‘A’

Can you do the calculations? You need to be able to use the equation triangle to calculate current or voltage or resistance. You must find a way of remembering the equation.

Using the triangle

The v_____ is a measure of how big a push the e_______ are given as they leave the cell or b_____. The bigger the voltage, the bigger the p___. The cell, battery or p____ s_____ produces the voltage. Voltage lamps oltage lectrons attery ush ower upply

Mains electricity We take mains electricity for granted – what exactly is it? How do we use it? Where does it come from?

Facts and figures Mains electricity has an alternating current a.c. This means it changes direction It does this 50 times a second – it has a frequency of 50 Hz It has voltage in the UK of 230 V

Where does mains electricity come from? Mains electricity is generated in power stations all around the country. It travels to our houses along a system of wires and pylons called the National Grid

How do we use it? We use 3 pin plugs to connect appliances to the mains.

Can you label the plug? Live terminal Neutral terminal Earth terminal Cable grip Fuse

For the following devices choose fuses from 3A, 5A and 13A. Operating Current Fuse 2.1A 11.2A 4.7A 6.0A 4.5A 8.2A 3.0A 13.0A 5.0A 13.0A 5.0A 13.0A Fuses II

How do you work out which fuse to use? You need to know another equation to calculate the current flowing through the appliance. This will tell you the correct rating of fuse to use. Power = Current x Voltage (P=IV)

Power = Current x Voltage Power is a measure of how fast an appliance transfers electrical energy Power is measured in watts (W) The higher the power – the faster the appliance works and the more electricity is uses You can use the power of an appliance to calculate how much electricity has been transferred in a given time

Power = energy transferred /time Power (W) = energy transferred (j) divided by the time taken (s) You will need to be able to use this equation. (You learnt it in physics 1a) Energy transferred./../. power x time