noadswood science, 2012. to understand current-potential difference graphs wednesday, may 13, 2015
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Noadswood Science, 2012
To understand current-potential difference graphs
Tuesday, April 18, 2023
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
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 1 Wire Type 2 Wire Type 3
Current (I) Voltage (V) Current (I) Voltage (V) Current (I) Voltage (V)
1 0 0 0 0 0.0 0
2 0.2 2 0.3 3 0.4 4
3 0.4 4 0.6 6 0.8 8
4 0.6 6 0.9 9 1.2 12
5 0.8 8 1.2 12 1.6 16
The current through a resistor (at constant temperature) is proportional to the voltage
Different wires have different resistances
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
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
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
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
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%
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%
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)
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