Class 12 Electric Charges And Fields CBSE Questions & Answers

Class 12 · Electric Charges And Fields

This is Physics Class 12 Electric Charges and Fields CBSE Questions & Answers. There are 15 questions in this test with each question having around four answer choices.

Questions & Answers

A point charge of 2.0 \(\mu {\rm{C}}\) is at the centre of a cubic Gaussian surface 9.0 cm on edge. What is the net electric flux through the surface?

A
\({\rm{2}}.{\rm{2 }} \times {\rm{ 1}}{0^{\rm{5}}}{\rm{N }}{{\rm{m}}^{\rm{2}}}/{\rm{C}}\)
B
\({\rm{2}}.{\rm{1 }} \times {\rm{ 1}}{0^{\rm{5}}}{\rm{N }}{{\rm{m}}^{\rm{2}}}/{\rm{C}}\)
C
\({\rm{1}}.{\rm{9 }} \times {\rm{ 1}}{0^{\rm{5}}}{\rm{N }}{{\rm{m}}^{\rm{2}}}/{\rm{C}}\)
Correct
D
A \({\rm{1}}.{\rm{7 }} \times {\rm{ 1}}{0^{\rm{5}}}{\rm{N }}{{\rm{m}}^{\rm{2}}}/{\rm{C}}\)

A point charge causes an electric flux of \(-{\rm{1}}.0{\rm{ }} \times {\rm{ 1}}{0^{\rm{3}}}{\rm{N}}{{\rm{m}}^{\rm{2}}}/{\rm{C}}\) to pass through a spherical Gaussian surface of 10.0 cm radius centred on the charge. (a) If the radius of the Gaussian surface were doubled, how much flux would pass through the surface? (b) What is the value of the point charge?

A
\( - {\rm{1}}{0^{\rm{3}}}{\rm{N }}{{\rm{m}}^{\rm{2}}}/{\rm{C}},-{\rm{8}}.{\rm{8 nC}}\)
Correct
B
B \({\rm{1}}{0^{\rm{3}}}{\rm{N }}{{\rm{m}}^{\rm{2}}}/{\rm{C}},-{\rm{8}}.{\rm{8 nC}}\)
C
\({\rm{1}}{0^{\rm{3}}}{\rm{N }}{{\rm{m}}^{\rm{2}}}/{\rm{C}},-{\rm{7}}.{\rm{8 nC}}\)
D
\( - {\rm{1}}{0^{\rm{3}}}{\rm{N }}{{\rm{m}}^{\rm{2}}}/{\rm{C}},-{\rm{6}}.{\rm{8 nC}}\)

A conducting sphere of radius 10 cm has an unknown charge. If the electric field 20 cm from the centre of the sphere is \({\rm{1}}.{\rm{5 }} \times {\rm{ 1}}{0^{\rm{3}}}{\rm{N}}/{\rm{C}}\) and points radially inward, what is the net charge on the sphere?

A
A –6.27 nC
B
6.67 nC
Correct
C
7.67 nC
D
7.27 nC

A uniformly charged conducting sphere of 2.4 m diameter has a surface charge density of \({\rm{8}}0.0{\rm{ }}\mu {\rm{C}}/{{\rm{m}}^{\rm{2}}}\). (a) Find the charge on the sphere. (b) What is the total electric flux leaving the surface of the sphere?

A
\({\rm{1}}.{\rm{35 }} \times {\rm{ 1}}0{^{ - {\rm{3}}}}{\rm{C}},{\rm{1}}.{\rm{6 }} \times {\rm{ 1}}0{^{\rm{8}}}{\rm{N}}{{\rm{m}}^{\rm{2}}}/{\rm{C}}\)
B
\({\rm{1}}.{\rm{45 }} \times {\rm{ 1}}0{^{ - {\rm{3}}}}{\rm{C}},{\rm{1}}.{\rm{6 }} \times {\rm{ 1}}0{^{\rm{8}}}{\rm{N}}{{\rm{m}}^{\rm{2}}}/{\rm{C}}\)
Correct
C
A \({\rm{1}}.{\rm{25 }} \times {\rm{ 1}}0{^{ - {\rm{3}}}}{\rm{C}},{\rm{1}}.{\rm{2 }} \times {\rm{ 1}}0{^{\rm{8}}}{\rm{N}}{{\rm{m}}^{\rm{2}}}/{\rm{C}}\)
D
\({\rm{1}}.{\rm{55 }} \times {\rm{ 1}}0{^{ - {\rm{3}}}}{\rm{C}},{\rm{1}}.{\rm{6 }} \times {\rm{ 1}}0{^{\rm{8}}}{\rm{N}}{{\rm{m}}^{\rm{2}}}/{\rm{C}}\)

Gravitational force is the smallest between

A
two pens weighing 100gms at a distance of 0.4 m
Correct
B
two books of weight 1kg each at a distance of 1 m
C
earth and the sun
D
earth and the sun

A solid metallic sphere has a charge + 3Q. Concentric with this sphere is a conducting spherical shell having charge –Q. The radius of the sphere is ‘a’ and that of spherical shell is ‘b’ (b>a). The electric field at a distance R \(\left( {{\rm{a}} < {\rm{r}}} \right)\)

A
A . \(\frac{4Q}{4πε_0 R^2 }\)
B
\(\frac{3Q}{4πε_0 R }\)
C
\(\frac{Q}{4πε_0 R }\)
D
\( \frac{3Q}{4πε_0 R^2 }\)
Correct

Six charges, each equal to + q, are placed at the corners of a regular hexagon of side a. The electric field at the point of intersection of diagonals is

A
\(\frac{1}{4\pi \epsilon_o }.\frac{6q}{a^2 }\)
B
\(\frac{1}{4\pi \epsilon_o }.\frac{q}{a^2 }\)
C
Zero
Correct
D
\(\frac{1}{4\pi \epsilon_o }.\frac{\sqrt{3q}}{2a^2 }\)

A pendulum bob of mass m carrying a charge q is at rest with its string making an angle θ with the vertical in a uniform horizontal electric field E. The tension in the string is

A
\(\frac{qE}{cos\theta }\)
B
\(\frac{qE}{sin\theta} \)
Correct
C
mg
D
\(\frac{mg}{sin\theta }\)

A point charge + q is placed at the mid point of a cube of side L. The electric flux emerging from the cube is

A
\(\frac{q}{6L^2\epsilon_o }\)
B
\(\frac{qL^2}{\epsilon_o }\)
C
zero
D
\(\frac{q}{\epsilon_o }\)
Correct

A particle of mass m and charge q is released from rest in a uniform electric field E. The kinetic energy attained by the particle after moving a distance x is

A
qEx
Correct
B
\({\rm{q E}}{{\rm{x}}^{\rm{2}}}\)
C
\({\rm{q}}{{\rm{E}}^{\rm{2}}}{\rm{x}}\)
D
\({{\rm{q}}^{\rm{2}}}{\rm{Ex}}\)

There is a uniform field of strength \({\rm{1}}{0^{\rm{3}}}{\rm{V}}{{\rm{m}}^{ - {\rm{1}}}}\) along the y-axis. A body of mass 1 g and charge \({\rm{1}}0{ - ^{ - {\rm{6}}}}\)C is projected into the field from the origin along the positive x-axis with a velocity of \({\rm{1}}0{\rm{ m}}{{\rm{s}}^{ - {\rm{1}}}}\). Its speed (in \({\rm{m}}{{\rm{s}}^{ - {\rm{1}}}}\) after 10 second will be (neglect gravitation)

A
\(5\sqrt 2 \)
B
\(10\sqrt 2 \)
Correct
C
10.0
D
20.0

A uniformly charged thin spherical shell of radius R carries uniform surface charge density of {tex}\sigma {tex} per unit area. It is made of two hemispherical shells, held together by pressing them with force F(See figure). F is proportional to

A
\(\frac{\sigma^2 R^2}{\epsilon_0}\)
Correct
B
\(\frac{\sigma^2 R}{\epsilon_0}\)
C
\(\frac{1}{\epsilon_0} \frac{\sigma^2 }{R^2}\)
D
\(\frac{1}{\epsilon_0} \frac{\sigma^2 }{R}\)

Two charges A = -2.50 \(\mu {\rm{C}}\) and B = 6.0 \(\mu {\rm{C}}\) are at a distance of 1 meter from each other. Distance from A at which the electric field is zero in meters is

A
2.03
B
2.22
C
1.92
D
1.82
Correct

A long, hollow conducting cylinder is kept coaxially inside another long, hollow conducting cylinder of larger radius. Both the cylinders are initially electrically neutral.

A
No potential difference appears between the two cylinders when a uniform line charge is kept along the axis of the cylinders.
B
A potential difference appears between the two cylinders when a charge density is given to the outer cylinder.
C
A potential difference appears between the two cylinders when a charge density is given to the inner cylinder.
Correct
D
No potential difference appears between the two cylinders when same charge density is given to both the cylinders.

Consider a neutral conducting sphere. A positive point charge is placed outside the sphere. The net charge on the sphere is then,

A
Negative and distributed non–uniformly over the entire surface of the sphere
B
Negative and distributed uniformly over the surface of the sphere.
C
Zero.
Correct
D
Negative and appears only at the point on the sphere closest to the point charge