Question:

The resistance of an ammeter is $13\, \Omega$ and its scale is graduated for a current upto $100\, A .$ After an additional shunt has been connected to this ammeter it becomes possible to measure currents upto $750\, A$ by this meter . The value of shunt resistance is

Updated On: Jul 5, 2022
  • $20\, \Omega$
  • $2\, \Omega$
  • $0.2\, \Omega$
  • $2 \,k\, \Omega$
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The Correct Option is B

Solution and Explanation

Let $i_{a}$ be the current flowing through ammeter and $i$ the total current. So, a current $i-i_{a}$ will flow through shunt resistance.
Potential difference across ammeter and shunt resistance is same, ie, $i_{a} \times R=\left(i-i_{a}\right) \times S$ or $S=\frac{i_{a} R}{i-i_{a}}$ Given, $i_{a}=100\, A,\, i=750\, A,\, R=13\, \Omega$ Hence, $S=\frac{100 \times 13}{750-100}=2\, \Omega$
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Questions Asked in AIIMS exam

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Concepts Used:

Resistance

Resistance is the measure of opposition applied by any object to the flow of electric current. A resistor is an electronic constituent that is used in the circuit with the purpose of offering that specific amount of resistance.

R=V/I

In this case,

v = Voltage across its ends

I = Current flowing through it

All materials resist current flow to some degree. They fall into one of two broad categories:

  • Conductors: Materials that offer very little resistance where electrons can move easily. Examples: silver, copper, gold and aluminum.
  • Insulators: Materials that present high resistance and restrict the flow of electrons. Examples: Rubber, paper, glass, wood and plastic.

Resistance measurements are normally taken to indicate the condition of a component or a circuit.

  • The higher the resistance, the lower the current flow. If abnormally high, one possible cause (among many) could be damaged conductors due to burning or corrosion. All conductors give off some degree of heat, so overheating is an issue often associated with resistance.
  • The lower the resistance, the higher the current flow. Possible causes: insulators damaged by moisture or overheating.