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The Dielectric constant of a medium is the ratio of the permittivity of the substance to the permittivity of free space

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Important Questions on Electric Charges and Fields

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

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

HARD

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

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

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

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

MEDIUM

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

A charge

Q

is placed at the centre of the line joining two equal charges

q

. The system of the three charges will be in equilibrium if

Q

is equal to

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

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

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

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

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

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>Coulomb's Laws

Two small spheres each of mass $10 mg$ are suspended from a point by threads $0.5 m$ long. They are equally charged and repel each other to a distance of $0.20 m$ . The charge on each of the sphere is $\frac{a}{21} \times 10^{- 8} C .$ The value of $a$ will be ___.[Given $g = 10 m s^{- 2}$ ]

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

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

HARD

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

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}} =

HARD

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

A charge $+ q$ is situated at a distance ' $d$ ' away from both the sides of a grounded conducting ' $L$ ' shaped sheet as shown in the figure.

Question Image

The force acting on the charge $+ q$ is

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

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

MEDIUM

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

Three charges

+ Q, q, + Q

are placed respectively, at distance,

0, d / 2

and

d

from the origin, on the

x

-axis. If the net force experienced by

+ Q,

placed at

x = 0,

is zero, then value of

q

is:

MEDIUM

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

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>Coulomb's Laws

Two identical conducting spheres with negligible volume have

2.1 nC

and

- 0.1 nC

charges, respectively. They are brought into contact and then separated by a distance of

0.5 m

. The electrostatic force acting between the spheres is ___

\times 10^{- 9} N

.
[Given :

4 π ε_{0} = \frac{1}{9 \times 10^{9}}

SI unit]

HARD

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

A negative charge is placed at the midpoint between two fixed equal positive charges, separated by a distance $2 d$ . If the negative charge is given a small displacement $x (x ≪ d)$ perpendicular to the line joining the positive charges, how the force $(F)$ developed on it will approximately depend on $x$ ?

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

If a charge

q

is placed at the centre of the line joining two equal charges

Q

such that the system is in equilibrium, then value of

q

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

Charges $Q_{1}$ and $Q_{2}$ are at points $A$ and $B$ of a right-angled triangle $O A B$ . The resultant electric field at point $O$ is perpendicular to the hypotenuse, then $Q_{1} / Q_{2}$ is proportional to:

Question Image

EASY

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

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

]

HARD

Physics>Electricity and Magnetism>Electric Charges and Fields>Coulomb's Laws

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

The Dielectric constant of a medium is the ratio of the permittivity of the substance to the permittivity of free space

Important Questions on Electric Charges and Fields

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