Question

A milli voltmeter of $25$ milli volt range is to be converted into an ammeter of $25$ ampere range. The value (in ohm) of necessary shunt will be

• A. 0.001
• B. 0.01
• C. 1
• D. 0.05

Answer 1

The Correct Option is A

To convert a milli voltmeter into an ammeter, a shunt resistor is used alongside the milli voltmeter. The function of the shunt resistor is to allow most of the current to pass through it, so only a small known portion of the current passes through the milli voltmeter.

Step 1: Understand the given parameters.

• The range of the milli voltmeter, \( V_m \), is 25 millivolts (0.025 volts).
• The desired range of the ammeter, \( I \), is 25 amperes.

Step 2: Apply the formula for the shunt resistor.

The formula relating the shunt resistor (\( R_s \)) with the full-range current of the ammeter and the voltage across the milli voltmeter is given by:

R_s = \frac{V_m}{I}

Step 3: Calculate the value of the shunt resistor.

Substituting the given values into the formula, we get:

R_s = \frac{0.025}{25} ohms

R_s = 0.001 ohms

Step 4: Conclusion.

The shunt resistor required to convert the milli voltmeter to an ammeter of 25 A range is 0.001 ohms.

This confirms that the correct option is 0.001 ohms, aligning with the provided options.

Key Insight: The shunt resistor provides an easy way to upgrade a voltage measuring device (like a milli voltmeter) into a current measuring device (ammeter) by handling a significant portion of the current.