Question

The internal resistance of a 2.1 V cell which gives a current of 0.2 A through a resistance of 10 Ω is

• A. 1.0 Ω
• B. 0.2 Ω
• C. 0.5 Ω
• D. 0.8 Ω

Hint:

Ohm’s law will be used to calculate the internal resistance of the cell through the values.

Answer 1

The Correct Option is C

To find the internal resistance of the cell, we apply Ohm's Law and consider the total resistance in the circuit.

Step 1: Understanding the situation

The cell provides a voltage V = 2.1 \, \text{V} and gives a current getting through an external resistor.

The given external resistance value is R = 10 \, \Omega.

The current through the circuit is I = 0.2 \, \text{A}.

Step 2: Applying Ohm's Law

According to Ohm's Law, the voltage across a resistor is given by:

V = I \times (R + r)

Where:

• V is the total voltage provided by the cell,
• I is the current,
• R is the external resistance,
• r is the internal resistance that we need to find.

Re-arranging the formula to find the internal resistance r:

r = \frac{V}{I} - R

Step 3: Substituting known values

We know that V = 2.1 \, \text{V}, I = 0.2 \, \text{A}, and R = 10 \, \Omega:

r = \frac{2.1}{0.2} - 10

r = 10.5 - 10

r = 0.5 \, \Omega

Conclusion: The internal resistance of the cell is 0.5 \, \Omega.

Therefore, the correct answer is 0.5 Ω.