Question

A galvanometer having a coil resistance of $60\, \Omega$ shows full scale deflection when a current of $1.0\, amp$ passes through it. It can be converted into an ammeter to read currents upto $5.0\, amp$ by

• A. putting in series a resistance of $15\, \Omega$
• B. putting in series a resistance of $240\, \Omega$
• C. putting in parallel a resistance of $15\, \Omega$
• D. putting in parallel a resistance of $240\, \Omega$

Answer 1

The Correct Option is C

To convert the given galvanometer into an ammeter that can read currents up to 5.0\, \text{A}, we need to consider the following calculations and deductions.

Given:

• Coil resistance of the galvanometer, R_g = 60\, \Omega
• Full-scale deflection current of the galvanometer, I_g = 1.0\, \text{A}
• Desired full-scale reading of the ammeter, I = 5.0\, \text{A}

To convert a galvanometer into an ammeter capable of reading higher currents, we need to place a shunt resistor (R_s) in parallel to the galvanometer. This shunt will divert the excess current.

The total current passes through the arrangement is I, out of which I_g passes through the galvanometer, and the remaining current (I - I_g) passes through the shunt resistor R_s.

Using the formula for the shunt resistance, we have: R_s = \frac{I_g \cdot R_g}{I - I_g}

Plugging in the values, we get: R_s = \frac{1.0\, \text{A} \times 60\, \Omega}{5.0\, \text{A} - 1.0\, \text{A}}

Calculating this gives: R_s = \frac{60}{4} = 15\, \Omega

Therefore, the required resistance to convert the galvanometer into an ammeter with a full-scale reading of 5.0\, \text{A} is 15\, \Omega, and it must be connected in parallel.

Thus, the correct answer is putting in parallel a resistance of 15\, \Omega.