Verifying Ohm's Law
When a resistor is kept at a constant temperature, its resistance will remain unchanged. We can confirm this experimentally by connecting a resistor to a The energy transferred each second, measured in watts (W). Power = work done ÷ time taken. supply and measuring the current in the resistor as the supply voltage is increased.
Plotting voltage (potential difference) against current for the resistor will produce a straight-line graph that passes through the origin.
Question
A torch lamp takes a current of 0.3 Unit of current, eg the current in the bulb is 4 amps or amperes (A). from a 3 volt A chemical supply of electrical energy. For example, common battery voltages include 1.5 V and 9 V.. Calculate its resistance.
\(V = IR\)
\(3 = 0.3 \times R\)
\(R = \frac{3}{{0.3}}\)
\(R = 10\Omega\)
\(R=10 ohms\)
Question
Calculate the reading on the ammeter in the circuit shown
\(I =\frac{V}{R}\)
\(=\frac{12}{2.7 \times 10^{3}}\)
\(= 4.4 \times 10^{-3}A\)
\(I = 4.4 \times 10^{-3}A\)
A change in temperature can cause a change in resistance for some materials. These materials are known as non-ohmic conductors.
For example, a thermistor’s resistance depends on its temperature.
A voltage-current graph for a thermistor is not a straight line.
This means that the resistance of the thermistor is not constant for different values of current. When the current decreases, the resistance of the thermistor increases.
