A shunt is a

Question

A shunt is a

Examoogle · Accepted Answer

Very low resistance

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.

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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