1. Noadswood Science, 2012

2.  To understand current-potential difference graphs Wednesday, May 13, 2015

3.  A graph of current against potential difference shows you how the current flowing through a component varies with the potential difference across it  The current is plotted on the vertical (y) axis; and the potential difference on the horizontal (x) axis

4.  Using the class data, plot a graph of the current-potential difference for the length of wire (plot the data for all three types of wire) Reading Wire Type 1Wire Type 2Wire Type 3 Current (I)Voltage (V)Current (I)Voltage (V)Current (I)Voltage (V) 100000.00 20.220.330.44 3 40.660.88 40.660.991.212 50.881.2121.616

5.  The current through a resistor (at constant temperature) is proportional to the voltage  Different wires have different resistances

6.  The current flowing through a resistor at a constant temperature is directly proportional to the potential difference across it – it is said to follow Ohm’s Law

7.  The filament lamp is a common type of light bulb (it contains a thin coil of wire called the filament)  The filament heats up when an electric current passes through it, and produces light as a result  The filament lamp does not follow Ohm’s Law – its resistance increases as the temperature of its filament increases  As voltage increases the bulb gets hotter, and its resistance increases

8.  Diodes are electronic components that can be used to regulate the potential difference in circuits and to make logic gates  Light-emitting diodes (LEDs) give off light and are often used for indicator lights in electrical equipment  The diode has a very high resistance in one direction – this means that current can only flow in one direction

9. Resistance = Voltage ÷ Current  For the straight-line graphs the resistance of the component is steady and is equal to the inverse of the gradient of the line (1/gradient)  The steeper the graph, the lower the resistance  If the graph curves the resistance is changing – calculated by taking the voltage divided by the current

10.  Resistance is anything which opposes an electric current  The resistance value of a resistor is shown by a series of coloured bands – each colour represents a number  Most resistors have 4 bands: - The first band gives the first digit The second band gives the second digit The third band indicates the number of zeros The fourth band is used to shows the tolerance (precision) of the resistor: - Red band = 2% Gold band = 5% Silver band = 10%

11.  Example – what is the resistor value?  This resistor has red (2), violet (7), yellow (4 zeros) and gold bands  Its value is 270’000 (270k)  Tolerance = 5%

12.  R means ohm  k means kilo-ohm (1k = 1 kilo-ohm; 1k8 = 1.8 kilo-ohms)  M means mega-ohm (2M = 2 mega-ohms; 2M2 – 2.2 mega-ohms)