# Electrostatics class 12 board questions (Electric charge and field)

This page contains electrostatics class 12 board questions. These questions are related to class 12 physics chapter 1 : Electric charge and fields. This is kind of simulated board exam paper only for chapter 1. You need to finish this paper in 3 hours. Take this test after you are confident in first chapter of class 12 physics.
General Instructions:
Time allowed : 3 hours                           Maximum marks : 70
(a) All questions are compulsory.
(b) There are 30 questions in total. Questions 1 to 8 carry one mark each, questions 9 to 18 carry two marks each, questions 19 to 27 carry three marks each and questions 28 to 30 carry five marks each.
(c) There is no overall choice. However, an internal choice has been provided in one question of two marks, one question of three marks and all three questions of five marks each. You have to attempt only one of the given choices in such questions.
(d) Use of calculators is not permitted.


## Electric charge and field questions

Question 1: How does positively charged glass rod attracts a neutral piece of paper?

Question 2: Vehicles carrying inflammable materials usually have metallic ropes touching the ground during motion. Why?

Question 3: What does $q_1+q_2=0$ signify in electrostatics?

Question 4: A charged particle is free to move in an electric field. Will it always move along an electric field?

Question 5: A positive charge $+q$ is kept in the vicinity of an uncharged conducting plate. Sketch electric field lines originating from the point charge on the surface of the plate.

Question 6: What are electric lines of forces? What is its importance?

Question 7: Two dipoles, made from charges $\pm q$ and$\pm Q$, respectively, have equal dipole moments. Give the (i) ratio between the separations of these two pairs of charges (ii) angle between the dipole axis of these two dipoles.

Question 8: Two charges of magnitudes $-2Q$ and $+Q$ are located at points $(a,0)$ and $(4a,0)$ respectively. What is the electric flux due to these charges through a sphere of radius $3a$ with its centre at the origin?

Question 9: State the law of conservation of charge.  Give two examples to illustrate it.

Question 10: Define electric field intensity and derive an expression for it at a point on the axial line of a dipole. Also, determine its direction.

Question 11: Use Gauss’s law to derive the expression for the electric field between two uniformly charged large parallel sheets with surface charge densities $\sigma$ and $-\sigma$ respectively

Question 12: Define electric line of force and give its two important properties.

Question 13: A thin straight infinitely long conducting wire having charge density $\lambda$ is enclosed by a cylindrical surface of radius $r$ and length $l$, its axis coinciding with the length of wire. Find the expression for the electric flux through the surface of the cylinder.

Question 14: State Coulomb’s law in vector form and prove that

${\vec F_{12}} = – {\vec F_{21}}$

where letters have their usual meaning.

Question 15: Two charges of $+10\mu C$ and $+40\mu C$ respectively are placed 12 cm apart. Find the position of the point where the electric field is zero.

Question 16: A uniformly charged conduction sphere of 2.4 m diameter has a surface charge density of $80.0\mu C/{{m}^{2}}$. (a) Find the charge on the sphere. (b) What is the total electric flux leaving the surface of the sphere?

Question 17: A charge +q is distributed uniformly over a thin rod of the length 2l. Calculate the electric field at a point P on the axis of the rod, at a distance r from its centre.

Question 18: Electric charge is distributed uniformly on the surface of a spherical rubber balloon. Show how the value of electric intensity vary

(i) on the surface       (ii) inside and         (iii) outside?

Question 19:  A polythene piece rubbed with wool is found to have a negative charge of 3.2 × 10–7 C. Calculate the no. of electrons transferred.

Question 20: Two charged conducting spheres of radii r1 and r2 connected to each other by a wire. Find the ratio of electric fields at the surfaces of the two spheres.

Question 21: While travelling back to his residence in the car, Dr Pathak was caught up in a thunderstorm. It became very dark. He stopped driving the car and waited for the thunderstorm to stop. Suddenly he noticed a child walking alone on the road. He asked the boy to come inside the car till the thunderstorm stopped. Dr Pathak dropped the boy at his residence. The boy insisted that Dr Pathak should meet his parents. The parents expressed their gratitude to Dr Pathak for his concern for the safety of the child. Answer the following questions based on the above information:

(a) Why is it safer to sit inside a car during a thunderstorm?

(b) Which two values are displayed by Dr Pathak in his actions?

(c) Which values are reflected in parents response to Dr Pathak?

(d) Give an example of a similar action on your part in the past from everyday life.

Question 22: State Gauss’s theorem in electrostatics. Using this theorem, derive an expression for electric field intensity due to an infinitely long straight wire of linear density $\lambda Cm^{-1}$.

Question 23: An electric dipole is held in a uniform electric field.

(i) using a suitable diagram, show that it does not undergo any translator motion.

(ii) derive an expression for the torque acting on it and specify its direction. When is this torque maximum?

Question 24: Prove that $\frac{1}{r^2}$ dependence of the electric field of a point charge is consistent with the concept of electric field lines.

Question 25: In a medium, the force of attraction between two point electric charges, distance $d$ apart is $F$. What distance apart should the charges be kept in the same medium so that the force between them becomes$3F$?

Question 26: Define the dielectric constant of the medium in terms of force between electric charges.

Question 27: Write a note about

(i) Conservation of charge

(ii) Quantization of charge

Question 28: Prove that for short dipole, the intensity at a point on the axial line is twice that on the equatorial line.

Question 29: Find the electric field intensity at any point on the axis of a uniformly charged ring or hoop.  What happens if the ring is far away from the point?

Question 30: A point charge $q$ is situated axially at a distance $r$ from one end of a thin non-conducting rod of length $L$ having a charge $Q$ distributed uniformly along its length. Find the magnitude of the electric force between the two.

Please note that I have not given the answers of these problems. These are meant to be practice questions. If you face any problem with these questions please feel free to discuss them in comments section given below. I'll be happy to help.