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#	Question	Answer
1	Who named the two kinds of charges as positive and negative?	Benjamin Franklin.
2	Give an example of a conductor.	Metals, human body, earth.
3	What is the value of the elementary charge \( e \)?	\( 1.602192 \times 10^{-19} \) C.
4	Who experimentally demonstrated the quantisation of charge?	Millikan.
5	What is the vector form of Coulomb's law?	\( \mathbf{F}_{21} = \frac{1}{4\pi\epsilon_0} \frac{q_1 q_2}{r_{21}^2} \hat{\mathbf{r}}_{21} \).
6	Who discovered Coulomb's law?	Charles Augustin de Coulomb.
7	Three charges each equal to \( q \) are placed at the vertices of an equilateral triangle. What is the force on a charge \( Q \) placed at the centroid?	Zero, by symmetry.
8	When two identical charged spheres are touched by uncharged spheres and the distance is halved, what happens to the force?	The force remains the same.
9	What is the direction of the electric field due to a positive charge?	Radially outwards.
10	What is a source charge?	The charge that produces the electric field.
11	A proton falls through 1.5 cm in a uniform electric field of \( 2.0 \times 10^4 \) N C⁻¹. What is the time of fall?	\( 1.3 \times 10^{-7} \) s.
12	What is the acceleration of a proton in a uniform electric field of \( 2.0 \times 10^4 \) N C⁻¹?	\( 1.9 \times 10^{12} \) m s⁻².
13	Where do electric field lines start and end?	They start from positive charges and end at negative charges.
14	Who invented the picture of field lines?	Michael Faraday.
15	What is the dipole moment?	\( \mathbf{p} = q \times 2a \hat{\mathbf{p}} \), directed from \( -q \) to \( q \).
16	For a closed surface, in which direction is the area vector taken?	Outward normal.
17	What are polar molecules?	Molecules that have a permanent electric dipole moment even in the absence of an external electric field.
18	What happens to a dipole in a non-uniform electric field?	It experiences both a net force and a torque.
19	What is Gauss's law?	The total electric flux through a closed surface is equal to \( \frac{q}{\epsilon_0} \), where \( q \) is the total charge enclosed by the surface.
20	What is the SI unit of volume charge density?	C m⁻³.
21	The electric field components are \( E_x = \alpha x^{1/2} \), \( E_y = E_z = 0 \). What is the flux through a cube of side a = 0.1 m if \( \alpha = 800 \) N/C m^{1/2}?	1.05 N m² C⁻¹.
22	What is the Gaussian surface chosen for an infinitely long charged wire?	A cylinder.
23	What is the electric field inside a uniformly charged thin spherical shell?	Zero (for \( r < R \)).
24	What are the three basic properties of electric charge?	Quantisation, additivity and conservation.
25	What is the electric field due to an infinite plane sheet?	\( E = \frac{\sigma}{2\epsilon_0} \).
26	Two point charges \( q_A = 3 \) µC and \( q_B = -3 \) µC are located 20 cm apart. What is the electric field at the midpoint?	\( 5.4 \times 10^6 \) N C⁻¹.
27	What is the net flux of a uniform electric field through a cube of side 20 cm?	Zero.
28	A uniformly charged conducting sphere of diameter 2.4 m has a surface charge density of 80.0 µC/m². What is the total charge on the sphere?	\( 1.45 \times 10^{-3} \) C.
29	What is the origin of the word "electricity"?	It is coined from the Greek word elektron, meaning amber.
30	What happens when charge is transferred to a conductor versus an insulator?	On a conductor, the charge readily distributes over the entire surface; on an insulator, it stays at the place it was put.
31	What are 1 µC (microcoulomb) and 1 mC (millicoulomb) in terms of coulombs?	1 µC = \( 10^{-6} \) C; 1 mC = \( 10^{-3} \) C.
32	What are the approximate electrostatic and gravitational forces between two protons inside a nucleus (separation ~\( 10^{-15} \) m)?	\( F_e \sim 230 \) N (repulsive); \( F_G \sim 1.9 \times 10^{-34} \) N (attractive).
33	Two point charges \( q_1=+10^{-8} \) C and \( q_2=-10^{-8} \) C are placed 0.1 m apart. What is the electric field at a point B, 0.05 m from \( q_1 \) (on the side away from \( q_2 \)) and 0.15 m from \( q_2 \)?	\( 3.2 \times 10^4 \) N C⁻¹, directed away from \( q_1 \) (towards the side opposite \( q_2 \)).
34	What does the experimental confirmation that the field inside a uniformly charged shell is zero verify about Coulomb's law?	It confirms the \( 1/r^2 \) (inverse-square) dependence in Coulomb's law.
35	In a non-uniform electric field, in which direction does a dipole whose moment p is antiparallel to E experience a net force?	Toward the direction of decreasing field strength.
36	Is there a known law analogous to charge quantisation for the quantisation of mass?	No — quantisation of electric charge is a basic, unexplained law of nature, but there is no analogous law of mass quantisation.
37	When a glass rod is rubbed with a silk cloth, charges appear on both. How is this consistent with conservation of charge?	Rubbing only transfers electrons from one body to the other — no charge is created or destroyed, so the rod and silk acquire equal and opposite charges, keeping the total charge of the system unchanged.
38	Two insulated charged copper spheres A and B, each with charge \( 6.5 \times 10^{-7} \) C, have centres 50 cm apart. What is the mutual force of electrostatic repulsion?	\( \approx 1.52 \times 10^{-2} \) N.
39	A uniformly charged conducting sphere of diameter 2.4 m has surface charge density 80.0 µC/m². What is the total electric flux leaving the surface of the sphere?	\( \approx 1.64 \times 10^8 \) N m² C⁻¹.
40	A charge of Q µC is placed at the centre of a cube. What is the electric flux through one face of the cube? (NEET 2023)	\( \frac{Q \times 10^{-6}}{6\epsilon_0} \) — by symmetry, the total flux \( Q\times10^{-6}/\epsilon_0 \) is shared equally among the cube's 6 faces.
41	Two parallel infinite line charges, \( +\lambda \) and \( -\lambda \), are separated by a distance 2R. What is the electric field midway between them? (NEET 2019)	\( \frac{\lambda}{\pi\epsilon_0 R} \), directed from the positive line toward the negative line — the fields from each line (magnitude \( \lambda/2\pi\epsilon_0 R \)) point the same way at the midpoint and add.