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1

### JEE Main 2021 (Online) 27th August Evening Shift

For full scale deflection of total 50 divisions, 50 mV voltage is required in galvanometer. The resistance of galvanometer if its current sensitivity is 2 div/mA will be :
A
1$$\Omega$$
B
5$$\Omega$$
C
4$$\Omega$$
D
2$$\Omega$$

## Explanation

$${I_{\max }} = {{50} \over 2} = 25$$ mA

$$R = {V \over I} = {{50mV} \over {25mA}} = 2\Omega$$
2

### JEE Main 2021 (Online) 27th August Evening Shift

The Colour coding on a carbon resistor is shown in the given figure. The resistance value of the given resistor is :

A
(5700 $$\pm$$ 285) $$\Omega$$
B
(7500 $$\pm$$ 750) $$\Omega$$
C
(5700 $$\pm$$ 375) $$\Omega$$
D
(7500 $$\pm$$ 375) $$\Omega$$

## Explanation

R = 75 $$\times$$ 102 $$\pm$$ 5% of 7500

R = (7500 $$\pm$$ 375) $$\Omega$$
3

### JEE Main 2021 (Online) 27th August Evening Shift

Three capacitors C1 = 2$$\mu$$F, C2 = 6$$\mu$$F and C3 = 12$$\mu$$F are connected as shown in figure. Find the ratio of the charges on capacitors C1, C2 and C3 respectively :

A
2 : 1 : 1
B
2 : 3 : 3
C
1 : 2 : 2
D
3 : 4 : 4

## Explanation

(VD $$-$$ V) C2 + (VD $$-$$ 0) C3 = 0

(VD $$-$$ V) 6 + (VD $$-$$ 0) 12 = 0

VD $$-$$ V + 2VD = 0

VD = $${V \over 3}$$

q2 = (V $$-$$ VD) C2 = $$\left( {V - {V \over 3}} \right)$$ (6 $$\mu$$F)

q2 = (4V) $$\mu$$F

q3 = (VD $$-$$ 0) C3 = $${{V \over 3}}$$ $$\times$$ 12$$\mu$$F = 4V$$\mu$$F

q1 = (V $$-$$ 0) C1 = V(2$$\mu$$F)

q1 : q2 : q3 = 2 : 4 : 4

q1 : q2 : q3 = 1 : 2 : 2
4

### JEE Main 2021 (Online) 27th August Morning Shift

Five identical cells each of internal resistance 1$$\Omega$$ and emf 5V are connected in series and in parallel with an external resistance 'R'. For what value of 'R', current in series and parallel combination will remain the same?
A
1 $$\Omega$$
B
25 $$\Omega$$
C
5 $$\Omega$$
D
10 $$\Omega$$

## Explanation

$${i_1} = {{25} \over {5 + R}}$$

$${i_2} = {5 \over {R + {1 \over 5}}}$$

$${i_1} = {i_2} \Rightarrow 5\left( {R + {1 \over 5}} \right) = 5 + R$$

4R = R

R = 1$$\Omega$$

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