1

### JEE Main 2019 (Online) 10th January Evening Slot

The actual value of resistance R, shown in the figure is 30$\Omega$. This is measuered in an experiment as shown using the standard formula R = ${V \over {\rm I}}$, where V and I are the readings of the voltmeter and ammeter, respectively. If the measured value of R is 5% less, then the internal resistance of the voltmeter is -

A
570 $\Omega$
B
600 $\Omega$
C
350 $\Omega$
D
35 $\Omega$

## Explanation

0.95 R = ${{R{R_v}} \over {R + {R_v}}}$

0.95 $\times$ 30 = 0.05 Rv

Rv = 19 $\times$ 30 = 570 $\Omega$
2

### JEE Main 2019 (Online) 11th January Morning Slot

Two equal resistances when connected in series to a battery, consume electric power of 60 W. If these resistances are now connected in parallel combination to the same battery, the electric power consumed will be :
A
240 W
B
60 W
C
30 W
D
120 W

## Explanation

In series condition, equivalent resistance is 2R

thus power consumed is 60W = ${{{\varepsilon ^2}} \over {2R}}$

In parallel condition, equivalent resistance is R/2 thus new power is

P' = ${{{\varepsilon ^2}} \over {\left( {R/2} \right)}}$

or   P' = 4P = 240W
3

### JEE Main 2019 (Online) 11th January Morning Slot

In the figure shown below, the charge on the left plate of the 10$\mu$F capacitor is –30$\mu$C. The charge on the right plate of the 6 $\mu$F capacitor is :

A
+ 12 $\mu$C
B
+ 18 $\mu$C
C
$-$ 18 $\mu$C
D
$-$ 12 $\mu$C

## Explanation

6$\mu$F & 4$\mu$F are in parallel & total charge on this combination is 30 $\mu$C

$\therefore$  Charge on 6$\mu$F capacitor = ${6 \over {6 + 4}} \times 30$

= 18 $\mu$C

Since charge is asked on right plate therefore is +18$\mu$C
4

### JEE Main 2019 (Online) 11th January Morning Slot

The given graph shows variation (with distance r form centre) of :

A
Electric field of a uniformly charged sphere
B
Electric field of a uniformly charged spherical shell
C
Potential of a uniformly charged sphere
D
Potential of a uniformly charged spherical shell

## Explanation

As the field inside the uniformly charged hollow sphere or spherical shell is zero, so the potential inside it is constant, whereas outside it varies inversely with distance.