Question

What is the approximate resistance setting of a rheostat in which $650$ mA of current flows with a $150$ V source?

Answer 1

Hint: Voltage is the charge difference between two positions. Current is the rate of charge flow. Resistance is a material's tendency to oppose the current. Ohm's law says that the current by a conductor between two locations is directly proportionate to the voltage across the two positions.

Complete step-by-step solution:
Given: Voltage, $V = 150 V$
Current, $I = 650 mA$
We will change the value of current from milliammeter to ammeter.
$I = 650 \times 10^{-3} A$
Potential difference is proportional to the current.
$V \propto I$
$V = IR$
We get,
$R = \dfrac{V}{I}$
Now, put the values of voltage and current in the above formula.
$R = \dfrac{150}{650 \times 10^{-3}}$
We get after solving,
$R = 0.2307 \times 10^{3} \Omega$
$\implies R = 230 \Omega$
Hence, the value of resistance setting of a rheostat in which $650$ mA of current flows with a $150 $ V source is $230 \Omega$.

Note:Ohm's law only holds if the given temperature and the other physical factors keep constant. In particular, components, rising the current increases the temperature. The light bulb's filament is an example of it, in which the temperature increases as the current is raised. In this case, Ohm's law cannot be implemented.