Heating Effect of Current and Electrical Measuring Instruments | Physics JEE previous year questions with Solutions

Q 1 :

A galvanometer has a coil of resistance $200 Ω$ with a full scale deflection at $20$ $μ A .$ The value of resistance to be added to use it as an ammeter of range $(0 - 20)$ $m A$ is [2024]

$0.40 Ω$
$0.20 Ω$
$0.50 Ω$
$0.10 Ω$

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(2)

$G = 200$ $Ω$ and $i_{g} = 20$ $μ A$

$i = i_{g} (\frac{G}{S} + 1)$

$\Rightarrow 20 \times 10^{- 3} = 20 \times 10^{- 6} (\frac{200}{S} + 1)$

$\Rightarrow \frac{200}{S} = 999 \Rightarrow S \approx 0.2 Ω$

Q 2 :

A galvanometer of resistance $100 Ω$ when connected in series with $400 Ω$ measures a voltage of up to 10 V. The value of resistance required to convert the galvanometer into an ammeter to read up to 10 A is $x \times 10^{- 2} Ω$ . The value of $x$ is [2024]

800
2
20
200

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(3)

For voltmeter,

$i_{g} = \frac{10}{400 + 100} = 20 \times 10^{- 3} A$

for ammeter

For ammeter

Let shunt resistance $= S$

$i_{g} R = (i - i_{g}) S$

$20 \times 10^{- 3} \times 100 = 10 S \Rightarrow S = 20 \times 10^{- 2} Ω$

Q 3 :

Three voltmeters, all having different internal resistances are joined as shown in figure. When some potential difference is applied across A and B, their readings are $V_{1}$ , $V_{2}$ and $V_{3}$ . Choose the correct option. [2024]

$V_{1} = V_{2}$
$V_{1} \neq V_{3} - V_{2}$
$V_{1} + V_{2} > V_{3}$
$V_{1} + V_{2} = V_{3}$

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(4)

From $KVL, V_{1} + V_{2} - V_{3} = 0 \Rightarrow V_{1} + V_{2} = V_{3}$

Q 4 :

A galvanometer having coil resistance $10 Ω$ shows a full scale deflection for a current of 3 mA. For it to measure a current of 8A, the value of the shunt should be: [2024]

$3 \times 10^{- 3} Ω$
$4.85 \times 10^{- 3} Ω$
$3.75 \times 10^{- 3} Ω$
$2.75 \times 10^{- 3} Ω$

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(3)

Given $G = 10 Ω, I_{g} = 3 mA and I = 8 A$

In case of conversion of galvanometer into ammeter.

We have $I_{g} G = (I - I_{g}) S$

$S = \frac{I_{g} G}{I - I_{g}} = \frac{(3 \times 10^{- 3}) \times 10}{8 - 0.003} = 3.75 \times 10^{- 3} Ω$

Q 5 :

The deflection in moving coil galvanometer falls from 25 divisions to 5 divisions when a shunt of $24 Ω$ is applied. The resistance of galvanometer coil will be ____ [2024]

$12 Ω$
$96 Ω$
$48 Ω$
$100 Ω$

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(2)

Let $x =$ current/division.

Without shunt,

After applying shunt,

$Now 5 x \times G = 20 x \times 24$

$G = 4 \times 24 = 96 Ω$

Q 6 :

A galvanometer has a resistance of 50 Ω and it allows maximum current of 5 mA. It can be converted into voltmeter to measure upto 100 V by connecting in series a resistor of resistance [2024]

5975 $Ω$
20050 $Ω$
19950 $Ω$
19500 $Ω$

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(3)

$= 20000 - 50 = 19950 Ω$

Q 7 :

In an ammeter, 5% of the main current passes through the galvanometer. If resistance of the galvanometer is G, the resistance of ammeter will be [2024]

$\frac{G}{20}$
$\frac{G}{199}$
$199$ $G$
$200$ $G$

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(1)

By using KVL

$I_{g} \cdot G = I_{S} \cdot S$

$S = \frac{I_{g} G}{I_{S}} = \frac{\frac{5}{100} I_{0}}{\frac{95}{100} I_{0}} G = \frac{1}{19} G$

$R_{A} = \frac{S G}{S + G} = \frac{\frac{G}{19} \cdot G}{\frac{G}{19} + G} = \frac{G^{2}}{\frac{19 \times 20 G}{19}} = \frac{G}{20}$

Q 8 :

In the given figure an ammeter A consists of a 240 $Ω$ coil connected in parallel to a 10 $Ω$ shunt. The reading of the ammeter is ______________ mA. [2024]

(160)

$R_{A} = \frac{G \cdot S}{G + S} = \frac{240 \times 10}{240 + 10} = \frac{240}{25} Ω = 9.6 Ω$

$R_{eq} = 140.4 + 9.6 = 150 Ω$

$\Rightarrow I = \frac{24}{150} = 160 mA$

Q 9 :

To determine the resistance (R) of a wire, a circuit is designed below. The V−I characteristic curve for this circuit is plotted for the voltmeter and the ammeter readings as shown in figure. The value of R is .......... $Ω$ . [2024]

(2500)

The resistance of the circuit, $R_{net} = \frac{V}{I} = \frac{4}{2 mA} = 2 \times 10^{3} Ω$

Equivalent resistance, $\frac{10^{3} \times 10 R}{10^{4} + R} = 2 \times 10^{3}$

$10^{4} R = 2 \times 10^{7} + 2 \times 10^{3} R$

$\Rightarrow R = \frac{10^{4}}{4} Ω = 2500 Ω$

Q 10 :

In the given circuit, the current flowing through the resistance 20 $Ω$ is 0.3 A, while the ammeter reads 0.9 A. The value of $R_{1}$ is ________ $Ω$ . [2024]

(30)

Given, $i_{1} = 0.3 A,$ $i_{1} + i_{2} + i_{3} = 0.9 A$

So, $V_{A B} = i_{1} \times 20 Ω = 20 \times 0.3 V = 6 V$

$i_{2} = \frac{6 V}{15 Ω} = \frac{2}{5} A$

$i_{1} + i_{2} + i_{3} = \frac{9}{10} A$

$\frac{3}{10} + \frac{2}{5} + i_{3} = \frac{9}{10} \Rightarrow i_{3} = 0.2 A$

$\Rightarrow (0.2) R_{1} = 6$

$\Rightarrow R_{1} = \frac{6}{0.2} = 30 Ω$

Q 11 :

Two resistance of 100 $Ω$ and 200 $Ω$ are connected in series with a battery of 4V and negligible internal resistance. A voltmeter is used to measure voltage across $100 Ω$ resistance, which gives reading as 1V. The resistance of voltmeter must be ________ $Ω$ . [2024]

(200)

Given potential across Voltmeter = 1V

$∴ Current in 100 Ω = \frac{1}{100} A = i_{1}$

$200 Ω = \frac{3}{100} A \Rightarrow$ as total potential $= 4 V_{1} & 1 V$ is drop across $100 Ω$

Let current in voltmeter = i

$i_{1} + i_{2} = i_{0}$

$i_{2} + \frac{1}{100} = \frac{3}{200}$

$i_{2} + \frac{3}{200} - \frac{1}{100} = \frac{1}{200} A_{1}$

$V = I R_{1} \Rightarrow 1 = \frac{1}{200} (r), \Rightarrow r = 200 Ω$

Q 12 :

Consider a moving coil galvanometer (MCG):

A. The torsional constant in moving coil galvanometer has dimensions [ ${ML}^{2} T^{- 2}$ ]

B. Increasing the current sensitivity may not necessarily increase the voltage sensitivity.

C. If we increase number of turns (N) to its double (2N), then the voltage sensitivity doubles.

D. MCG can be converted into an ammeter by introducing a shunt resistance of large value in parallel with galvanometer.

E. Current sensitivity of MCG depends inversely on number of turns of coil.

Choose the correct answer from the options given below: [2025]

A, B only
A, D only
B, D, E only
A, B, E only

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(1)

(A) $τ = C θ \Rightarrow [{ML}^{2} T^{- 2}] = [C] [1]$

(B) $C . S . = \frac{θ}{I} = \frac{BNA}{C};$

$V . S . = \frac{BNA}{RC}$ [R = also depends on 'N']

(C) $V . S . \propto \frac{NAB}{CR} R \to NR$

(D) Shunt of law of resistance, False [Theory]

(E) E [False] C.S $\propto$ N

$\Rightarrow C . S = \frac{NAB}{C}$

Q 13 :

A galvanometer having a coil of resistance 30 $Ω$ need 20 mA of current for full-scale deflection. If a maximum current of 3 A is to be measured using this galvanometer, the resistance of the shunt to be added to the galvanometer should be $\frac{30}{X} Ω$ , where X is [2025]

447
298
149
596

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(3)

$I_{g} R_{g} = (I - I_{g}) r_{s}$

$20 \times 10^{- 3} \times 30 = (3 - 0.02) \times r_{s}$

$r_{s} = (\frac{0.6}{2.98}) = \frac{30}{x}$

$x = (\frac{2.98 \times 30}{0.6}) = 149$

Q 14 :

In a moving coil galvanometer, two moving coils $M_{1}$ and $M_{2}$ have the following particulars:

$R_{1} = 5 Ω, N_{1} = 15, A_{1} = 3.6 \times 10^{- 3} m^{2}, B_{1} = 0.25 T$

$R_{2} = 7 Ω, N_{2} = 21, A_{2} = 1.8 \times 10^{- 3} m^{2}, B_{2} = 0.50 T$

Assuming that torsional constant of the springs are same for both coils, what will be the ratio of voltage sensitivity of $M_{1}$ and $M_{2}$ ? [2025]

1 : 1
1 : 4
1 : 3
1 : 2

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(1)

$K θ = N I A B \Rightarrow \frac{θ}{I} = \frac{N A B}{K}$

Voltage sensitivity $= \frac{θ}{V} = \frac{θ}{R I} = \frac{N A B}{K R}$

Ratio of voltage sensitivity $= (\frac{N_{1} A_{1} B_{1}}{R_{1}}) (\frac{R_{2}}{N_{2} A_{2} B_{2}})$

Ratio $= (\frac{N_{1} A_{1} B_{1}}{N_{2} A_{2} B_{2}}) \frac{R_{2}}{R_{1}} = \frac{15 \times 3.6 \times 0.25}{21 \times 1.8 \times 0.5} \times \frac{7}{5} = \frac{1}{1}$

Q 15 :

A cell of emf 90 V is connected across series combination of two resistors each of 100 $Ω$ resistance. A voltmeter of resistance 400 $Ω$ is used to measure the potential difference across each resistor. The reading of the voltmeter will be [2023]

45 V
40 V
80 V
90 V

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(2)

$R_{eq} = \frac{400 \times 100}{500} + 100 = 180 Ω$

$i = \frac{90}{180} = \frac{1}{2} A$

$Reading = \frac{1}{2} \times \frac{400}{500} \times 100 = 40 V$

Q 16 :

The number of turns of the coil of a moving coil galvanometer is increased in order to increase current sensitivity by 50%. The percentage change in voltage sensitivity of the galvanometer will be [2023]

100%
50%
75%
0%

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(4)

$Current sensitivity = Voltage sensitivity \times R$

$Current sensitivity is made 1.5 times.$

$R also increases 1.5 times.$

$Hence voltage sensitivity = \frac{1.5 \times current sensitivity}{1.5 \times R} = no change$

Q 17 :

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R. [2023]

Assertion A: For measuring the potential difference across a resistance of 600 $Ω$ , the voltmeter with resistance 1000 $Ω$ will be preferred over voltmeter with resistance 4000 $Ω$ .

Reason R: Voltmeter with higher resistance will draw smaller current than voltmeter with lower resistance.

In the light of the above statements, choose the most appropriate answer from the options given below.

A is not correct but R is correct
Both A and R are correct and R is the correct explanation of A
Both A and R are correct but R is not the correct explanation of A
A is correct but R is not correct

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(1)

Error of voltmeter decreases with increase in its resistance.

Q 18 :

A student is provided with a variable voltage source $V$ , a test resistor $R_{r} = 10 Ω$ , two identical galvanometers $G_{1}$ and $G_{2}$ , and two additional resistors, $R_{1} = 10 M Ω$ and $R_{2} = 0.001 Ω$ . For conducting an experiment to verify Ohm's law, the most suitable circuit is [2023]

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(3)

To convert galvanometer into ammeter low resistance should be added in parallel and for voltmeter conversion, a very high resistance should be added in series.

Q 19 :

For designing a voltmeter of range 50 V and an ammeter of range 10 mA using a galvanometer which has a coil of resistance 54 $Ω$ showing a full-scale deflection for 1 mA as shown in figure. [2023]

(A) for voltmeter $R \approx 50 k Ω$
(B) for ammeter $r \approx 0.2 Ω$
(C) for ammeter $r \approx 6 Ω$
(D) for voltmeter $R \approx 5 k Ω$
(E) for voltmeter $R \approx 500 Ω$

Choose the correct answer from the options given below:

(C) and (E)
(C) and (D)
(A) and (C)
(A) and (B)

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(3)

$For voltmeter$

$R = \frac{V}{I_{g}} - G = \frac{50}{10^{- 3}} - 54 \approx 50 k Ω (A)$

$For ammeter$

$S = \frac{I_{g} G}{I - I_{g}} = \frac{10^{- 3} \times 54}{(10 - 1) \times 10^{- 3}} = 6 Ω (C)$

Q 20 :

As shown in the figure, the voltmeter reads 2 V across 5 $Ω$ resistor. The resistance of the voltmeter is ______ $Ω$ . [2023]

(20)

$i_{1} = \frac{2 V}{5 Ω} = \frac{2}{5} A$

$i = \frac{1 V}{2 Ω} = \frac{1}{2} A$

$∴$ $Current through voltmeter = i - i_{1}$

$= \frac{1}{2} - \frac{2}{5} = \frac{5 - 4}{10} = \frac{1}{10} A$

$∴$ $For voltmeter 2 = (\frac{1}{10}) R \Rightarrow R = 20 Ω$

Q 21 :

When a resistance of 5 $Ω$ is shunted with a moving coil galvanometer, it shows a full scale deflection for a current of 250 mA; however, when 1050 $Ω$ resistance is connected with it in series, it gives full scale deflection for 25 volt. The resistance of the galvanometer is ______ $Ω$ . [2023]

(50)

$\frac{250 mA \times 5}{5 + R_{G}} = i$ ...(i)

$i = \frac{25}{1050 + R_{G}}$ ...(ii)

$From (i) and (ii),$

$\frac{25}{1050 + R_{G}} = \frac{5}{4 (5 + R_{G})}$

$100 (5 + R_{G}) = 1050 \times 5 + R_{G} \times 5$

$95 R_{G} = 4750 \Rightarrow R_{G} = 50 Ω$

Q 22 :

A moving coil galvanometer of resistance 100 $Ω$ shows a full scale deflection for a current of 1 mA. The value of resistance required to convert this galvanometer into an ammeter, showing full scale deflection for a current of 5 mA, is ________ $Ω$ [2026]

0.5
10
2.5
25

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(4)

$G = 100 Ω$

$i_{g} = 1 mA$

$i = 5 mA$

$r_{s} = \frac{G}{(\frac{i}{i_{g}} - 1)}$

$= \frac{100}{(\frac{5}{1} - 1)} = 25 Ω$

Topic Question Set

Q 1 :

A galvanometer has a coil of resistance $200 Ω$ with a full scale deflection at $20$ $μ A .$ The value of resistance to be added to use it as an ammeter of range $(0 - 20)$ $m A$ is [2024]

Q 2 :

A galvanometer of resistance $100 Ω$ when connected in series with $400 Ω$ measures a voltage of up to 10 V. The value of resistance required to convert the galvanometer into an ammeter to read up to 10 A is $x \times 10^{- 2} Ω$ . The value of $x$ is [2024]

Q 3 :

Three voltmeters, all having different internal resistances are joined as shown in figure. When some potential difference is applied across A and B, their readings are $V_{1}$ , $V_{2}$ and $V_{3}$ . Choose the correct option. [2024]

Q 4 :

A galvanometer having coil resistance $10 Ω$ shows a full scale deflection for a current of 3 mA. For it to measure a current of 8A, the value of the shunt should be: [2024]

Q 5 :

The deflection in moving coil galvanometer falls from 25 divisions to 5 divisions when a shunt of $24 Ω$ is applied. The resistance of galvanometer coil will be ____ [2024]

Q 6 :

A galvanometer has a resistance of 50 Ω and it allows maximum current of 5 mA. It can be converted into voltmeter to measure upto 100 V by connecting in series a resistor of resistance [2024]

Q 7 :

In an ammeter, 5% of the main current passes through the galvanometer. If resistance of the galvanometer is G, the resistance of ammeter will be [2024]

Q 8 :

In the given figure an ammeter A consists of a 240 $Ω$ coil connected in parallel to a 10 $Ω$ shunt. The reading of the ammeter is ______________ mA. [2024]

Q 9 :

To determine the resistance (R) of a wire, a circuit is designed below. The V−I characteristic curve for this circuit is plotted for the voltmeter and the ammeter readings as shown in figure. The value of R is .......... $Ω$ . [2024]

Q 10 :

In the given circuit, the current flowing through the resistance 20 $Ω$ is 0.3 A, while the ammeter reads 0.9 A. The value of $R_{1}$ is ________ $Ω$ . [2024]

Q 11 :

Two resistance of 100 $Ω$ and 200 $Ω$ are connected in series with a battery of 4V and negligible internal resistance. A voltmeter is used to measure voltage across $100 Ω$ resistance, which gives reading as 1V. The resistance of voltmeter must be ________ $Ω$ . [2024]

Q 13 :

A galvanometer having a coil of resistance 30 $Ω$ need 20 mA of current for full-scale deflection. If a maximum current of 3 A is to be measured using this galvanometer, the resistance of the shunt to be added to the galvanometer should be $\frac{30}{X} Ω$ , where X is [2025]

Q 15 :

A cell of emf 90 V is connected across series combination of two resistors each of 100 $Ω$ resistance. A voltmeter of resistance 400 $Ω$ is used to measure the potential difference across each resistor. The reading of the voltmeter will be [2023]

Q 16 :

The number of turns of the coil of a moving coil galvanometer is increased in order to increase current sensitivity by 50%. The percentage change in voltage sensitivity of the galvanometer will be [2023]

Q 20 :

As shown in the figure, the voltmeter reads 2 V across 5 $Ω$ resistor. The resistance of the voltmeter is ______ $Ω$ . [2023]

Q 22 :

A moving coil galvanometer of resistance 100 $Ω$ shows a full scale deflection for a current of 1 mA. The value of resistance required to convert this galvanometer into an ammeter, showing full scale deflection for a current of 5 mA, is ________ $Ω$ [2026]

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Topic Question Set

Q 1 : A galvanometer has a coil of resistance 200Ω with a full scale deflection at 20 μA. The value of resistance to be added to use it as an ammeter of range (0-20) mA is [2024]

Q 2 : A galvanometer of resistance 100Ω when connected in series with 400Ω measures a voltage of up to 10 V. The value of resistance required to convert the galvanometer into an ammeter to read up to 10 A is x×10-2Ω. The value of x is [2024]

Q 3 : Three voltmeters, all having different internal resistances are joined as shown in figure. When some potential difference is applied across A and B, their readings are V1, V2 and V3. Choose the correct option. [2024]

Q 4 : A galvanometer having coil resistance 10Ω shows a full scale deflection for a current of 3 mA. For it to measure a current of 8A, the value of the shunt should be: [2024]

Q 5 : The deflection in moving coil galvanometer falls from 25 divisions to 5 divisions when a shunt of 24Ω is applied. The resistance of galvanometer coil will be ____ [2024]

Q 6 : A galvanometer has a resistance of 50 Ω and it allows maximum current of 5 mA. It can be converted into voltmeter to measure upto 100 V by connecting in series a resistor of resistance [2024]

Q 7 : In an ammeter, 5% of the main current passes through the galvanometer. If resistance of the galvanometer is G, the resistance of ammeter will be [2024]

Q 8 : In the given figure an ammeter A consists of a 240Ω coil connected in parallel to a 10Ω shunt. The reading of the ammeter is ______________ mA. [2024]

Q 9 : To determine the resistance (R) of a wire, a circuit is designed below. The V−I characteristic curve for this circuit is plotted for the voltmeter and the ammeter readings as shown in figure. The value of R is .......... Ω. [2024]

Q 10 : In the given circuit, the current flowing through the resistance 20 Ω is 0.3 A, while the ammeter reads 0.9 A. The value of R1 is ________ Ω. [2024]

Q 11 : Two resistance of 100Ω and 200Ω are connected in series with a battery of 4V and negligible internal resistance. A voltmeter is used to measure voltage across 100Ω resistance, which gives reading as 1V. The resistance of voltmeter must be ________ Ω. [2024]

Q 13 : A galvanometer having a coil of resistance 30 Ω need 20 mA of current for full-scale deflection. If a maximum current of 3 A is to be measured using this galvanometer, the resistance of the shunt to be added to the galvanometer should be 30XΩ, where X is [2025]

Q 15 : A cell of emf 90 V is connected across series combination of two resistors each of 100Ω resistance. A voltmeter of resistance 400Ω is used to measure the potential difference across each resistor. The reading of the voltmeter will be [2023]

Q 16 : The number of turns of the coil of a moving coil galvanometer is increased in order to increase current sensitivity by 50%. The percentage change in voltage sensitivity of the galvanometer will be [2023]

Q 18 : A student is provided with a variable voltage source V, a test resistor Rr=10Ω, two identical galvanometers G1 and G2, and two additional resistors, R1=10 MΩ and R2=0.001 Ω. For conducting an experiment to verify Ohm's law, the most suitable circuit is [2023]

Q 20 : As shown in the figure, the voltmeter reads 2 V across 5Ω resistor. The resistance of the voltmeter is ______ Ω. [2023]

Q 21 : When a resistance of 5Ω is shunted with a moving coil galvanometer, it shows a full scale deflection for a current of 250 mA; however, when 1050Ω resistance is connected with it in series, it gives full scale deflection for 25 volt. The resistance of the galvanometer is ______ Ω. [2023]

Q 22 : A moving coil galvanometer of resistance 100 Ω shows a full scale deflection for a current of 1 mA. The value of resistance required to convert this galvanometer into an ammeter, showing full scale deflection for a current of 5 mA, is ________ Ω [2026]

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Q 1 :

A galvanometer has a coil of resistance $200 Ω$ with a full scale deflection at $20$ $μ A .$ The value of resistance to be added to use it as an ammeter of range $(0 - 20)$ $m A$ is [2024]

Q 2 :

A galvanometer of resistance $100 Ω$ when connected in series with $400 Ω$ measures a voltage of up to 10 V. The value of resistance required to convert the galvanometer into an ammeter to read up to 10 A is $x \times 10^{- 2} Ω$ . The value of $x$ is [2024]

Q 3 :

Three voltmeters, all having different internal resistances are joined as shown in figure. When some potential difference is applied across A and B, their readings are $V_{1}$ , $V_{2}$ and $V_{3}$ . Choose the correct option. [2024]

Q 4 :

A galvanometer having coil resistance $10 Ω$ shows a full scale deflection for a current of 3 mA. For it to measure a current of 8A, the value of the shunt should be: [2024]

Q 5 :

The deflection in moving coil galvanometer falls from 25 divisions to 5 divisions when a shunt of $24 Ω$ is applied. The resistance of galvanometer coil will be ____ [2024]

Q 6 :

A galvanometer has a resistance of 50 Ω and it allows maximum current of 5 mA. It can be converted into voltmeter to measure upto 100 V by connecting in series a resistor of resistance [2024]

Q 7 :

In an ammeter, 5% of the main current passes through the galvanometer. If resistance of the galvanometer is G, the resistance of ammeter will be [2024]

Q 8 :

In the given figure an ammeter A consists of a 240 $Ω$ coil connected in parallel to a 10 $Ω$ shunt. The reading of the ammeter is ______________ mA. [2024]

Q 9 :

To determine the resistance (R) of a wire, a circuit is designed below. The V−I characteristic curve for this circuit is plotted for the voltmeter and the ammeter readings as shown in figure. The value of R is .......... $Ω$ . [2024]

Q 10 :

In the given circuit, the current flowing through the resistance 20 $Ω$ is 0.3 A, while the ammeter reads 0.9 A. The value of $R_{1}$ is ________ $Ω$ . [2024]

Q 11 :

Two resistance of 100 $Ω$ and 200 $Ω$ are connected in series with a battery of 4V and negligible internal resistance. A voltmeter is used to measure voltage across $100 Ω$ resistance, which gives reading as 1V. The resistance of voltmeter must be ________ $Ω$ . [2024]

Q 13 :

A galvanometer having a coil of resistance 30 $Ω$ need 20 mA of current for full-scale deflection. If a maximum current of 3 A is to be measured using this galvanometer, the resistance of the shunt to be added to the galvanometer should be $\frac{30}{X} Ω$ , where X is [2025]

Q 15 :

A cell of emf 90 V is connected across series combination of two resistors each of 100 $Ω$ resistance. A voltmeter of resistance 400 $Ω$ is used to measure the potential difference across each resistor. The reading of the voltmeter will be [2023]

Q 16 :

The number of turns of the coil of a moving coil galvanometer is increased in order to increase current sensitivity by 50%. The percentage change in voltage sensitivity of the galvanometer will be [2023]

Q 20 :

As shown in the figure, the voltmeter reads 2 V across 5 $Ω$ resistor. The resistance of the voltmeter is ______ $Ω$ . [2023]

Q 22 :

A moving coil galvanometer of resistance 100 $Ω$ shows a full scale deflection for a current of 1 mA. The value of resistance required to convert this galvanometer into an ammeter, showing full scale deflection for a current of 5 mA, is ________ $Ω$ [2026]