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Consider an initially neutral hollow conducting spherical shell with inner radius $r$ and outer radius $2 r$ . A point charge $+ Q$ is now placed inside the shell at a distance $\frac{r}{2}$ from the centre. The shell is then grounded by connecting the outer surface to the earth. $P$ is an external point at a distance $2 r$ from the point charge $+ Q$ on the line passing through the centre and the point charge $+ Q$ as shown in the figure.

The magnitude of the force on a test charge $+ q$ placed at $P$ will be

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Important Questions on Electrostatics

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Practice Book for KVPY Aptitude Test - Stream SA Physics>Chapter 13 - Electrostatics>Exercise 2>Q 8

Two positively charged spheres of masses

m_{1}

and

m_{2}

, are suspended from a common point at the ceiling by identical insulating massless strings of length

l

. Charges on the two spheres are

q_{1}

and

q_{2}

, respectively. At equilibrium both strings make the same angle

θ

with the vertical. Then

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Practice Book for KVPY Aptitude Test - Stream SA Physics>Chapter 13 - Electrostatics>Exercise 2>Q 9

Two equal charges of magnitude

Q

each are placed at a distance

d

apart. Their electrostatic energy is

E . A .

third charge

- \frac{Q}{2}

is brought midway between these two charges. The electrostatic energy of the system is now?

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Practice Book for KVPY Aptitude Test - Stream SA Physics>Chapter 13 - Electrostatics>Exercise 2>Q 10

Two small metal balls of different mass

m_{1}

and

m_{2}

are connected by strings of equal length to a fixed point. When the balls are given charges, the angles that the two strings make with the vertical are

30 °

and

60 °

, respectively. The ratio

\frac{m_{1}}{m_{2}}

, is close to

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Practice Book for KVPY Aptitude Test - Stream SA Physics>Chapter 13 - Electrostatics>Exercise 2>Q 11

An electric field due to a positively charged long straight wire at a distance

r

from it is proportional to

r^{- 1}

in magnitude. Two electrons are orbiting such a long straight wire in circular orbits of radii

1 \overset{\circ}{A}

and

2 \overset{\circ}{A}

. The ratio of their respective time periods is

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Practice Book for KVPY Aptitude Test - Stream SA Physics>Chapter 13 - Electrostatics>Exercise 2>Q 12

20 g

bullet whose specific heat is

5000 J {kg}^{- 1} {}^{\circ}C^{- 1}

and moving at

2000 m s^{- 1}

plunges into a

1.0 kg

block of wax whose specific heat is

3000 J {kg}^{- 1} {}^{\circ}C^{- 1}

. Both bullet and wax are at

25 ° C

and assume that

(i)

the bullet comes to rest in the wax and

(ii)

all its kinetic energy goes into heating the wax. Thermal temperature of the wax in

{}^{\circ}C

is close to.

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Practice Book for KVPY Aptitude Test - Stream SA Physics>Chapter 13 - Electrostatics>Exercise 2>Q 13

Positive point charges are placed at the vertices of a star shape as shown in the figure.
Question Image

Direction of the electrostatic force on a negative point charge at the centre

O

of the star is

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Practice Book for KVPY Aptitude Test - Stream SA Physics>Chapter 13 - Electrostatics>Exercise 2>Q 14

A total solar eclipse is observed from the earth. At the same time, an observer on the moon views the earth. She is most likely to see (E denotes the earth)
Question Image

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Practice Book for KVPY Aptitude Test - Stream SA Physics>Chapter 13 - Electrostatics>Exercise 2>Q 15

A proton of mass

m

and charge

e

is projected from a very large distance towards an

α

particle with velocity

v

. Intially,

α

particle is at rest, but it is free to move. If gravity is neglected, then the minimum separation along the straight line of their motion will be

Important Questions on Electrostatics

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