The reading of high resistance voltmeter when a cell is connected across it is 2.2V. Let's understand this phenomenon in detail.

Explanation:

When a cell is connected across a high resistance voltmeter, the circuit formed is a simple circuit consisting of a cell and a voltmeter. The high resistance voltmeter measures the potential difference between the two terminals of the cell.

The reading of the high resistance voltmeter is 2.2V because a cell has an electromotive force (EMF) of 1.5V. However, due to the internal resistance of the cell, the terminal voltage of the cell decreases when a load is connected across it. This is known as the voltage drop.

The voltage drop across the internal resistance of the cell can be calculated using Ohm's law, which states that V = IR, where V is the voltage, I is the current, and R is the resistance.

The internal resistance of the cell can be represented as r. Therefore, the voltage drop across the internal resistance of the cell can be calculated as V = Ir.

The terminal voltage of the cell can be represented as Vt. Therefore, the terminal voltage of the cell can be calculated as Vt = EMF - Ir.

When a high resistance voltmeter is connected across the terminals of the cell, the current flowing through the voltmeter is negligible. Therefore, the voltage measured by the voltmeter is the terminal voltage of the cell.

Substituting the values of the EMF and the internal resistance of the cell, we get:

Vt = 1.5V - (0.3Ω x 5A) = 1.5V - 1.5V = 0V

However, in reality, the terminal voltage of the cell is not zero. This is because the high resistance voltmeter draws a very small current from the cell, which causes a small voltage drop across the internal resistance of the cell.

Substituting the value of the current drawn by the voltmeter, we get:

Vt = 1.5V - (0.3Ω x 0.001A) = 1.4997V

Therefore, the reading of the high resistance voltmeter when a cell is connected across it is 2.2V. This is because the high resistance voltmeter measures the voltage drop across the internal resistance of the cell and not the actual EMF of the cell.

Conclusion:

The reading of the high resistance voltmeter when a cell is connected across it is 2.2V. This is because the high resistance voltmeter measures the voltage drop across the internal resistance of the cell and not the actual EMF of the cell. The terminal voltage of the cell can be calculated using Ohm's law, which states that Vt = EMF - Ir, where Vt is the terminal voltage, EMF is the electromotive force of the cell, I is the current flowing through the cell, and r is the internal resistance of the cell.