Q: A galvanometer of resistance 99\,\Omega gives full-scale deflection at 10\text{ mA}. To convert it into an ammeter of range 0–1\text{ A}, the shunt required is:

1\,\Omega. S = \dfrac{I_gG}{I - I_g} = \dfrac{0.01 \times 99}{1 - 0.01} = \dfrac{0.99}{0.99} = 1\,\Omega.

Question 1

A moving coil galvanometer is an instrument used to:

Accepted Answer

Detect and measure small electric currents. The current-carrying coil experiences a torque in the field of a permanent magnet, and the deflection measures the current.

Question 2

In a moving coil galvanometer, the current sensitivity is defined as:

Accepted Answer

The deflection produced per unit current. Current sensitivity is \dfrac{	heta}{I} = \dfrac{NAB}{k}, where k is the torsion constant of the suspension.

Question 3

A galvanometer is converted into an ammeter by connecting:

Accepted Answer

A low resistance in parallel with it. The shunt carries most of the current and keeps the combined resistance low, as an ammeter must have.

Question 4

A galvanometer is converted into a voltmeter by connecting:

Accepted Answer

A high resistance in series with it. The series multiplier limits the current and gives the instrument the high resistance a voltmeter needs.

Question 5

The resistances of an ideal ammeter and an ideal voltmeter are respectively:

Accepted Answer

Zero and infinite. An ideal ammeter drops no voltage in the circuit, and an ideal voltmeter draws no current from it.

Question 6

In a circuit, an ammeter and a voltmeter are connected respectively:

Accepted Answer

In series and in parallel with the element. An ammeter must carry the current being measured; a voltmeter must experience the potential difference being measured.

Question 7

The voltage sensitivity of a galvanometer is defined as:

Accepted Answer

The deflection produced per unit potential difference. Voltage sensitivity equals current sensitivity divided by the galvanometer resistance.

Question 8

Increasing the current sensitivity of a galvanometer does not necessarily increase its voltage sensitivity because:

Accepted Answer

The change may also increase the coil resistance. Adding turns raises NAB but also lengthens the coil, raising G; voltage sensitivity \dfrac{NAB}{kG} may then be unchanged.

Question 9

A galvanometer of resistance 99\,\Omega gives full-scale deflection at 10	ext{ mA}. To convert it into an ammeter of range 0–1	ext{ A}, the shunt required is:

Accepted Answer

1\,\Omega. S = \dfrac{I_gG}{I - I_g} = \dfrac{0.01 	imes 99}{1 - 0.01} = \dfrac{0.99}{0.99} = 1\,\Omega.

Question 10

A galvanometer of resistance 50\,\Omega gives full-scale deflection at 2	ext{ mA}. To convert it into a voltmeter of range 0–10	ext{ V}, the series resistance required is:

Accepted Answer

4950\,\Omega. R_s = \dfrac{V}{I_g} - G = \dfrac{10}{0.002} - 50 = 5000 - 50 = 4950\,\Omega.

Question 11

A galvanometer of resistance 100\,\Omega gives full-scale deflection at 1	ext{ mA}. The shunt needed to convert it into an ammeter of range 0–1	ext{ A} is approximately:

Accepted Answer

0.1\,\Omega. S = \dfrac{0.001 	imes 100}{1 - 0.001} = \dfrac{0.1}{0.999} \approx 0.1\,\Omega.

Question 12

A galvanometer of resistance 20\,\Omega gives full-scale deflection at 5	ext{ mA}. To read up to 5	ext{ V}, the series resistance required is:

Accepted Answer

980\,\Omega. R_s = \dfrac{5}{0.005} - 20 = 1000 - 20 = 980\,\Omega.

Question 13

A galvanometer of resistance 10\,\Omega gives full-scale deflection at 10	ext{ mA}. The shunt needed for a range of 0–0.1	ext{ A} is approximately:

Accepted Answer

1.11\,\Omega. S = \dfrac{0.01 	imes 10}{0.1 - 0.01} = \dfrac{0.1}{0.09} \approx 1.11\,\Omega.

Question 14

A galvanometer of resistance 60\,\Omega gives full-scale deflection at 1	ext{ mA}. To read up to 3	ext{ V}, the series resistance required is:

Accepted Answer

2940\,\Omega. R_s = \dfrac{3}{0.001} - 60 = 3000 - 60 = 2940\,\Omega.

Question 15

The shunt resistance required to convert a galvanometer of resistance G and full-scale current I_g into an ammeter of range I is:

Accepted Answer

\dfrac{I_gG}{I - I_g}. The shunt must carry I - I_g while the same potential difference appears across both branches.

Question 16

A galvanometer of resistance 40\,\Omega gives full-scale deflection at 5	ext{ mA}. To read up to 2	ext{ V}, the series resistance required is:

Accepted Answer

360\,\Omega. R_s = \dfrac{2}{0.005} - 40 = 400 - 40 = 360\,\Omega.

Question 17

A galvanometer shows a deflection of 30 divisions for a current of 2	ext{ mA}. Its current sensitivity is:

Accepted Answer

15 divisions per milliampere. Current sensitivity = \dfrac{30}{2} = 15 divisions per milliampere.

Question 18

A galvanometer of resistance 99\,\Omega gives full-scale deflection at 1	ext{ mA}. The shunt needed for a range of 0–0.1	ext{ A} is:

Accepted Answer

1\,\Omega. S = \dfrac{0.001 	imes 99}{0.1 - 0.001} = \dfrac{0.099}{0.099} = 1\,\Omega.

Question 19

When a shunt is connected across a galvanometer, the resistance of the resulting ammeter is:

Accepted Answer

Less than both the galvanometer resistance and the shunt resistance. The two are in parallel, and a parallel combination is always smaller than either branch.

Question 20

To double the range of a voltmeter made from a galvanometer, the required series resistance must be:

Accepted Answer

More than doubled, since the galvanometer resistance is subtracted only once. From R_s = \dfrac{V}{I_g} - G, doubling V doubles the first term but G is still subtracted once, so R_s becomes slightly more than twice as large.

Moving Coil Galvanometer & Conversions — MH-CET Physics MCQs with Solutions

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