Option C: Very low resistance Explanation & Concepts: A shunt is a very low-value resistance connected in parallel with a measuring instrument (typically a PMMC galvanometer) to extend its current-measuring range. By diverting a significant portion of the total current away from the meter movement, it prevents the instrument coil from being damaged by excessive current. Working Principle: According to the principle of current division, when a low resistance $R_{sh}$ is placed in parallel with a meter resistance $R_m$, the majority of the current $I$ flows through the path of least resistance. The shunt resistance is precisely calculated so that the meter only receives its full-scale deflection current $I_m$, while the remainder $I_{sh} = I - I_m$ flows through the shunt. Key Formulas: $R_{sh} = \frac{R_m}{m - 1}$ — where $m = \frac{I}{I_m}$ is the multiplying power of the shunt; $I_{sh} = I - I_m$ — Current division at the shunt junction Key Points: Shunt resistance must always be in parallel with the moving coil instrument.; A lower $R_{sh}$ value results in a higher multiplying power ($m$) for the ammeter.; The shunt material is typically Manganin, chosen for its low temperature coefficient of resistance. Advantages: Allows measurement of very high currents using a standard low-range galvanometer.; Provides a protective bypass for the meter movement. Disadvantages: Increases heat dissipation if not sized correctly.; Accuracy depends on the thermal stability of the shunt material. Applications: Range extension of DC ammeters.; Current sensing in motor control drives and battery management systems. Additional Info: The resistance of the shunt is typically much smaller than the internal resistance of the meter ($R_{sh} \ll R_m$).. Option A and D are incorrect because high resistance in parallel would not bypass enough current to protect the meter. Answer: C is correct — A shunt is a very low resistance connected in parallel to an ammeter to extend its current measuring range. Exam Tip: Remember that a 'shunt' always implies parallel connection, while a 'multiplier' (used for voltmeters) always implies series connection.

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ElectricalMeasurement & Instrumentation

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A shunt is a

Very high resistance

Medium resistance

Very low resistance

High resistance

Correct Answer

Concept & PrincipleElectricalMeasurement & Instrumentation

Option C

Very low resistance

Quick Summary: A shunt is a very low-value resistance connected in parallel with a measuring instrument (typically a PMMC galvanometer) to extend its current-measuring range. By diverting a significant portion of the total current away from the meter movement, it prevents the instrument coil from being damaged by excessive current.

💡 Explanation

A shunt is a very low-value resistance connected in parallel with a measuring instrument (typically a PMMC galvanometer) to extend its current-measuring range. By diverting a significant portion of the total current away from the meter movement, it prevents the instrument coil from being damaged by excessive current.

🔢 Key Formulas

$R_{sh} = \frac{R_m}{m - 1}$ — where $m = \frac{I}{I_m}$ is the multiplying power of the shunt

$I_{sh} = I - I_m$ — Current division at the shunt junction

⚙️ Working Principle

According to the principle of current division, when a low resistance $R_{sh}$ is placed in parallel with a meter resistance $R_m$ , the majority of the current $I$ flows through the path of least resistance. The shunt resistance is precisely calculated so that the meter only receives its full-scale deflection current $I_m$ , while the remainder $I_{sh} = I - I_m$ flows through the shunt.

📌 Key Points

▸
Shunt resistance must always be in parallel with the moving coil instrument.
▸
A lower $R_{sh}$ value results in a higher multiplying power ( $m$ ) for the ammeter.
▸
The shunt material is typically Manganin, chosen for its low temperature coefficient of resistance.

✅ Advantages

▸
Allows measurement of very high currents using a standard low-range galvanometer.
▸
Provides a protective bypass for the meter movement.

❌ Disadvantages / Limitations

▸
Increases heat dissipation if not sized correctly.
▸
Accuracy depends on the thermal stability of the shunt material.

🛠️ Applications / Uses

▸
Range extension of DC ammeters.
▸
Current sensing in motor control drives and battery management systems.

📄 Additional Information

▸
The resistance of the shunt is typically much smaller than the internal resistance of the meter ( $R_{sh} \ll R_m$ ).
▸
Option A and D are incorrect because high resistance in parallel would not bypass enough current to protect the meter.

📊 Diagram / Illustration

✅

C is correct — A shunt is a very low resistance connected in parallel to an ammeter to extend its current measuring range.

Core Concepts Used

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Current Division Rule PMMC Instrument Modification Multiplying Power of Shunt

💡 EXAM TIP

Remember that a 'shunt' always implies parallel connection, while a 'multiplier' (used for voltmeters) always implies series connection.

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