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A table tennis ball, covered with conducting paint, is suspended by a silk thread so that it hang between two plates. Out of these, one is earthed and other is connected to a high voltage generator. This ball,

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Important Questions on Electric Charges and Fields

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Two point charges A and B, having charges

+ Q

and

- Q

respectively, are placed at certain distance apart and force acting between them is

F

. If

25 %

charge of

A

is transferred to

B

, then the force between the charges becomes

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Suppose the charge of a proton and an electron differ slightly. One of them is

e

, the other is

(e + Δ e)

. If the net electrostatic force and gravitational force between two hydrogen atoms placed at a distance

d

(much greater than atomic size) apart is zero, then

Δ e

is of the order of [Given mass of hydrogen

m_{h} = 1.67 \times 10^{- 27} kg

]

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Two charges of equal magnitudes and at a distance $r$ exert a force $F$ on each other. If the charges are halved and distance between them is doubled, then the new force acting on each charge is

MEDIUM

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Three charges are placed at the three vertices of an equilateral triangle of side $a$ as shown in the figure. The force experienced by the charge placed at the vertex $A$ in a direction normal to $B C$ is

Question Image

MEDIUM

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

A length - scale

(l)

depends on the permittivity

(ε)

of a dielectric material, Boltzmann constant

k_{B}

, the absolute temperature T, the number per unit volume (n) of certain charged particles, and the charge (q) carried by each of the particles, Which of the following expressions (s) for

l

is (are) dimensionally correct?

HARD

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Two identical non-conducting solid spheres of same mass and charge are suspended in air from a common point by two non-conducting, massless strings of same length. At equilibrium, the angle between the strings is

α

. The spheres are now immersed in a dielectric liquid of density

800 kg m^{- 3}

and dielectric constant

21

. If the angle between the strings remains the same after the immersion, then

MEDIUM

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Three concentric metal shells

A, B

and

C

of respective radii

a, b

and

c (a < b < c)

have surface charge densities

+ σ, - σ

and

+ σ

respectively. The potential of shell

B

is:

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Four point charges $q_{A} = 2 μ C, q_{B} = - 5 μ C, q_{C} = 2 μ C, q_{D} = - 5 μ C$ are located at the corners of a square $A B C D$ of side $10 cm .$ The force acting on a charge of $1 μ C$ placed at centre of the square is

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HARD

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Two charges, each equal to

q

, are kept at

x = - a

and

x = a

on the x-axis. A particle of mass

m

and charge

q_{0} = - \frac{q}{2}

is placed at the origin. If charge

q_{0}

is given a small displacement

(y ≪ a)

along the y-axis, the net force acting on the particle is proportional to :

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

The dimensional formula of coefficient of permittivity for free space (

ε_{0}

) in the equation

F = \frac{1}{4 π ε_{0}} \frac{q_{1} q_{2}}{r^{2}},

where symbols have their usual meanings, is

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Two electrons are moving with equal speed of

5 \times 10^{5} m s^{- 1}

parallel to each other. The ratio of the electrostatic to the magnetic force between them is

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Two identical conducting spheres A and B carry equal charge. They are initially separated by a distance much larger than their diameters and the force between them is F. A third identical conducting sphere C is uncharged. Sphere C is first touched to A, then to C and removed. As a result, the force between A and B now is

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Two small metal spheres

A

and

B

charged positively are separated by

2 m

in air. The force on a charge of

+ 1 C

placed on the line joining the centres of the spheres and at a distance of

0.5 m

from

A

is found to be zero. The ratio

q_{A} : q_{B}

of charges on

A

and

B

HARD

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

A certain charge

2 Q

is divided at first into two parts

q_{1}

and

q_{2}

. Later the charges are placed at a certain distance. If the force of interaction between two charges is maximum then

\frac{Q}{q_{1}} =

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Three Point charges each equal to

+ q

are placed at the vertices of an equilateral triangle of side

' l'

. The net force on a charge

q_{1}

placed at the centre of the triangle is

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Two equally charged metal spheres

A

and

B

repel each other with a force of

4 \times 10^{- 5} N

. Another identical uncharged sphere

C

is touched to

A

and then placed at the mid point of the line joining the spheres

A

and

B

. The net electric force on the sphere

C

MEDIUM

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Three identical charges each of magnitude

3 μ C

are placed at the corners of a right angled triangle

ABC

whose base

B C

and height

B A

are

3 cm

and

4 cm

respectively. Forces on the charge at right angled corner

B

due to charges at

A

and

C

are

F_{1}

and

F_{2}

respectively. The angle between their resultant force and

F_{2}

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Two identical conducting spheres

A

and

B

carry an equal charges. They are separated by a distance much larger than their diameters, and the force between them is

F

. A third identical conducting sphere,

C

, is uncharged. Sphere

C

is first touched to

A

, then to

B

, and then removed. As a result, the force between

A

and

B

would be equal to:

HARD

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Two identical charged spheres suspended from a common point by two massless strings of lengths

l

, are initially at a distance

d (d ≪ l)

apart because of their mutual repulsion. The charges begin to leak from both the spheres at a constant rate. As a result, the spheres approach each other with a velocity

υ

. Then

υ

varies as a function of the distance

x

between the spheres, as

HARD

Physics>Electricity and Magnetism>Electric Charges and Fields>Different Methods of Charging

Two isolated conducting spheres

S_{1}

and

S_{2}

of radius

\frac{2}{3} R

and

\frac{1}{3} R

have

12 μ C

and

- 3 μ C

charges, respectively, and are at a large distance from each other, They are now connected by a conducting wire. A long time after this is done the charges on

S_{1}

and

S_{2}

are respectively:

A table tennis ball, covered with conducting paint, is suspended by a silk thread so that it hang between two plates. Out of these, one is earthed and other is connected to a high voltage generator. This ball,

Important Questions on Electric Charges and Fields

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