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Current Electricity question

2024 · 5 Apr · Shift 1 · Q85
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  5. /2024 · 5 Apr · Shift 1 · Q85

Current Electricity question

2024 · 5 Apr · Shift 1 · Q85

JEE MainPhysicsCurrent ElectricityNumerical+4 / −1
In the experiment to determine the galvanometer resistance by half-deflection method, the plot of 1/θ1 / \theta1/θ vs the resistance (R) of the resistance box is shown in the figure. The figure of merit of the galvanometer is ‾\underline{\hspace{2cm}}​×10−1 A/\times 10^{-1} \mathrm{~A} /×10−1 A/ division. [The source has emf 2 V2 \mathrm{~V}2 V] JEE Main 2024 (Online) 5th April Morning Shift Physics - Current Electricity Question 30 English
Numerical answer
View written solutionFree

Correct answer: 5

  1. Half-deflection setup relation

For a galvanometer of resistance GGG, cell emf EEE, series resistance RRR, and figure of merit kkk:

Ig=ER+GI_g = \frac{E}{R+G}Ig​=R+GE​

If the galvanometer shows deflection θ\thetaθ, then

Ig=kθI_g = k\thetaIg​=kθ

So,

kθ=ER+Gk\theta = \frac{E}{R+G}kθ=R+GE​

Rearranging,

1θ=kE(R+G)=kER+kGE\frac{1}{\theta} = \frac{k}{E}(R+G) = \frac{k}{E}R + \frac{kG}{E}θ1​=Ek​(R+G)=Ek​R+EkG​

Thus, the graph of 1θ\dfrac{1}{\theta}θ1​ vs RRR is a straight line with slope

m=kEm = \frac{k}{E}m=Ek​

Hence,

k=mEk = mEk=mE


  1. Read slope from the graph

From the given straight-line plot, the slope is

m=0.25  division−1 Ω−1m = 0.25\; \text{division}^{-1}\,\Omega^{-1}m=0.25division−1Ω−1

(Equivalently, if two convenient points are read, the rise/run gives 0.250.250.25.)


  1. Calculate figure of merit

Given

E=2 VE = 2\,\text{V}E=2V

Therefore,

k=mE=0.25×2=0.50  A/divisionk = mE = 0.25 \times 2 = 0.50\;\text{A/division}k=mE=0.25×2=0.50A/division

Since the answer is to be written in the form

‾×10−1  A/division\underline{\hspace{1cm}} \times 10^{-1}\;\text{A/division}​×10−1A/division

we write

0.50=5×10−10.50 = 5 \times 10^{-1}0.50=5×10−1

So the figure of merit is

5×10−1  A/division\boxed{5 \times 10^{-1}\;\text{A/division}}5×10−1A/division​

Hence, the required integer is:

5\boxed{5}5​

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