State Ohm's Law - Leaving Cert Physics - Question 8 - 2005

The metal conductor obeys Ohm’s law as evidenced by the straight line graph (a) shown in the diagram. This linear relationship indicates that the current is directly proportional to voltage, fulfilling the criteria of Ohm’s law. In contrast, the filament bulb (graph b) shows a nonlinear relationship, indicating that it does not obey Ohm's law.

To find the total resistance of the circuit (R_total), we sum the resistances of the two components in series:

$R_{total} = R_1 + R_2 = 100 \Omega + 500 \Omega = 600 \Omega$

Using Ohm's Law, the current (I) can be calculated using the total resistance and the voltage (V):

$I = \frac{V}{R_{total}} = \frac{6 \text{ V}}{600 \Omega} = 0.01 \text{ A}$

The potential difference (V_1) across the 100 Ω resistor can be found using Ohm's Law:

$V_1 = I \times R_1 = 0.01 \text{ A} \times 100 \Omega = 1 \text{ V}$

As the thermistor heats up, its resistance decreases due to its negative temperature coefficient characteristics, which means it becomes more conductive.

As the resistance of the thermistor decreases, the total resistance of the circuit decreases, leading to an increase in the current flowing in the circuit. Consequently, the potential difference across the 100 Ω resistor will also increase as long as it has constant resistance.

Thermistors are commonly used as temperature sensors in devices such as thermostats, where they help to regulate the temperature by monitoring changes in heat and adjusting systems accordingly.