Question:

A galvanometer of 25 ohms and having full scale deflection for a current of 10 mA is changed into voltmeter of range 100 volts by connecting a resistance R in series with the galvanometer. The resistance R in ohms is:

Updated On: Jan 18, 2023
  • 10000
  • 975
  • 10025
  • 9975
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The Correct Option is D

Solution and Explanation

Using formula for resistance R $ R=\frac{V}{{{i}_{g}}}-G $ Here, $ G=25\,\Omega , $ $ {{i}_{g}}=10\times {{10}^{-3}}A, $ $ V=100\,V $ On putting the value in above formula, we get $ =\frac{100}{10\times {{10}^{-3}}}-25 $ $ =1000-25 $ $ =9975\,ohm $
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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.