View all 36 cards in this deck

#	Question	Answer
1	What is a conservative force?	A force for which the work done in moving a body from one point to another is independent of the path taken.
2	What is the relation between potential energy and potential?	\( U = qV \).
3	What is the electrostatic potential due to a point charge \( Q \) at a distance \( r \)?	\( V = \frac{Q}{4\pi\epsilon_0 r} \).
4	What is the potential due to a dipole on its axial line?	\( V = \pm\frac{p}{4\pi\epsilon_0 r^2} \) — positive on the side of \( +q \) (\( \theta = 0 \)), negative on the side of \( -q \) (\( \theta = \pi \)).
5	What is the potential due to a system of charges at a point?	\( V = \frac{1}{4\pi\epsilon_0} \sum_{i=1}^{n} \frac{q_i}{r_{iP}} \).
6	Does the potential obey the principle of superposition?	Yes.
7	What is an equipotential surface?	A surface with a constant value of potential at all points on the surface.
8	What is the potential energy of a system of three charges?	\( U = \frac{1}{4\pi\epsilon_0} \left( \frac{q_1 q_2}{r_{12}} + \frac{q_1 q_3}{r_{13}} + \frac{q_2 q_3}{r_{23}} \right) \).
9	What is the potential energy of a charge \( q \) in an external potential \( V(\mathbf{r}) \)?	\( U = qV(\mathbf{r}) \).
10	What is the energy gained by an electron accelerated through a potential difference of 1 V?	1 eV.
11	What is the potential energy of a dipole in a uniform external field?	\( U = -\mathbf{p} \cdot \mathbf{E} \).
12	Is the electrostatic potential constant throughout a conductor?	Yes.
13	What is the electric field at the surface of a charged conductor?	\( E = \frac{\sigma}{\epsilon_0} \hat{n} \).
14	Give an example of a polar molecule.	H₂O or HCl.
15	What is polarisation?	The dipole moment per unit volume of a dielectric.
16	What is the capacitance of a parallel plate capacitor?	\( C = \frac{\epsilon_0 A}{d} \).
17	What is the capacitance of a parallel plate capacitor with a dielectric of dielectric constant \( K \)?	\( C = \frac{K\epsilon_0 A}{d} \).
18	A slab of dielectric constant \( K \) and thickness \( \frac{3}{4}d \) is inserted between the plates of a parallel plate capacitor. What is the new capacitance?	\( C = \frac{4K}{K+3} C_0 \).
19	What is the equivalent capacitance of capacitors connected in parallel?	\( C = C_1 + C_2 + \cdots + C_n \).
20	Is the equivalent capacitance of capacitors in parallel greater or less than the largest individual capacitance?	Greater.
21	What is the energy density of an electric field?	\( u = \frac{1}{2} \epsilon_0 E^2 \).
22	What is the equivalent capacitance of capacitors in series?	\( \frac{1}{C} = \frac{1}{C_1} + \frac{1}{C_2} + \cdots \).
23	A parallel plate capacitor with air between the plates has a capacitance of 8 pF. What is the capacitance if the distance is reduced by half and the space is filled with a dielectric of constant 6?	96 pF.
24	What is the electric energy density?	\( \frac{1}{2} \epsilon_0 E^2 \).
25	Does the kinetic energy of a small negative charge increase or decrease as it moves closer to another negative point charge?	Decrease — the force of repulsion slows it down.
26	Why can a capacitor have a strong electric field between its plates while still having only a small potential difference?	A capacitor confines the field lines to a small region of space (the narrow gap between the plates), so even a strong field over that tiny separation corresponds to a small potential difference (V = Ed).
27	Does electrostatic shielding work "the other way round" — i.e. does the exterior of a conductor get shielded from charges placed inside a cavity within it?	No — a cavity is shielded from outside fields, but placing charges inside the cavity does affect the fields outside the conductor (the exterior is not shielded from the inside charges).
28	Inside a uniformly polarised dielectric (away from its surfaces), what is the net charge in a small volume element, even though it has a net dipole moment?	Zero — the positive charge of one molecular dipole sits next to the negative charge of the adjacent dipole, so they cancel everywhere except at the surfaces.
29	A comb run through dry hair attracts small bits of paper. Why does this not happen if the hair is wet or it is a rainy day?	Friction between hair and comb is reduced when wet, so the comb does not get charged, and an uncharged comb cannot polarise and attract the paper.
30	Two charges 2 µC and −2 µC are placed at points A and B, 6 cm apart. What is an equipotential surface of this system, and what is the field direction on it?	The plane normal to AB and bisecting it is an equipotential surface (at zero potential); the electric field on it is normal to this plane, directed from A towards B.
31	A parallel plate capacitor (air between plates) has plates of area \( 6\times10^{-3} \) m² separated by 3 mm. What is its capacitance, and what charge does it hold at 100 V?	\( C \approx 17.7 \) pF; \( Q \approx 1.77 \times 10^{-9} \) C.
32	Which of these statements about a charged conductor in electrostatic equilibrium are correct: (A) field inside is zero, (B) surface field is independent of surface charge density, (C) the interior has no excess charge, (D) the surface field is normal to the surface, (E) the potential is zero everywhere inside? (NEET 2026)	A, C, and D are correct. (B is false — surface field is \( \sigma/\epsilon_0 \), which depends on \( \sigma \); E is false — the interior potential is constant, not necessarily zero.)
33	The capacitance of a capacitor with charge q and potential V depends on which of these: q, V, or the geometry of the conductors? (NEET 2024)	Only the geometry (shape, size, and separation) of the conductors — C = Q/V is independent of both Q and V individually.
34	Two hollow conducting spheres of radii \( R_1 \gg R_2 \) carry equal charge. Which has the greater surface potential? (NEET 2022)	The smaller sphere (radius \( R_2 \)) — since \( V = q/4\pi\epsilon_0 R \) for the same q, a smaller R gives a larger V.
35	A short dipole has dipole moment \( 16\times10^{-9} \) C m. What is the potential at a point 0.6 m away, on a line making 60° with the dipole axis? (NEET 2020)	200 V.
36	For a uniformly charged conducting sphere of radius R and charge Q, what are the potential and the electric field exactly at its centre? (AIPMT 2014)	Potential = \( \frac{Q}{4\pi\epsilon_0 R} \) (same as the surface value, since the interior is equipotential); field = 0 (interior field is always zero).