1.The SI unit of electric charge is ____________.
Ans: Coulomb ($\text{C}$)
2.The magnitude of elementary charge on a proton is exactly ____________ C.
Ans: $1.6 \times 10^{-19}$
3.When a glass rod is rubbed with silk, the glass rod acquires a ____________ charge.
Ans: Positive
4.Which of the following is the true test of electrification?
Ans: (B) Repulsion (because attraction can happen between a charged body and a neutral body due to induction).
5.The number of electrons present in $1\text{ C}$ of charge is approximately:
Ans: (A) $6.25 \times 10^{18}$ (Calculated from $n = q/e = 1 / 1.6 \times 10^{-19}$).
6.The law of conservation of charge states that:
Ans: (D) All of the above are correct interpretations.
7.Define the quantization of charge and state its formula.
Ans: Charge exists only in discrete integral multiples of the elementary charge. Formula: $q = ne$ (where $n = 0, \pm 1, \pm 2...$).
8.What does the equation $q_1 + q_2 = 0$ signify in electrostatics?
Ans: It signifies that the two charges are equal in magnitude but opposite in sign ($q_1 = -q_2$).
9.Can a physical body have a total charge of $4.8 \times 10^{-19}\text{ C}$? Give a reason.
Ans: Yes. $n = q/e = (4.8 \times 10^{-19}) / (1.6 \times 10^{-19}) = 3$. Since $n$ is an integer, this charge is possible.
10.Distinguish basically between conductors and insulators.
Ans: Conductors have free electrons and allow charge to flow freely. Insulators tightly bind electrons and resist charge flow.
11.What is meant by the process of "grounding" or "earthing"?
Ans: The process of sharing excess charge of a body directly with the Earth by connecting them with a conductor.
12.What is charging by induction?
Ans: Charging a neutral conductor by bringing a charged object nearby without physically touching it.
13.Match the following concepts correctly:
Ans: (a) $\rightarrow$ (iii) Deficiency of electrons
(b) $\rightarrow$ (ii) Excess of electrons
(c) $\rightarrow$ (i) Given by $q = ne$
14.The numerical value of $1/(4\pi\epsilon_0)$ in vacuum is ____________ $\text{Nm}^2/\text{C}^2$.
Ans: $9 \times 10^9$
15.The constant $\epsilon_0$ is known as the ____________ of free space.
Ans: permittivity
16.The electrostatic force between two point charges separated by distance $r$ is proportional to:
Ans: (D) $1/r^2$ (Inverse square law)
17.If a dielectric medium of constant $K$ is introduced... the force between them:
Ans: (B) decreases $K$ times ($F_{medium} = F_{vacuum}/K$)
18.Relative permittivity (Dielectric constant) $\epsilon_r$ is defined as the ratio:
Ans: (B) $\epsilon / \epsilon_0$
19.State Coulomb's law in electrostatics.
Ans: Force between two point charges is directly proportional to the product of charges and inversely proportional to the square of distance between them.
20.Write Coulomb's law strictly in vector form.
Ans: $\vec{F}_{12} = \frac{1}{4\pi\epsilon_0} \frac{q_1 q_2}{r^2} \hat{r}_{21}$
21.What is the accepted dielectric constant ($K$) for a perfectly conducting metal?
Ans: Infinity ($\infty$).
22.State the principle of superposition for electrostatic forces.
Ans: Net force on a charge is the vector sum of all independent Coulomb forces exerted on it by other charges.
23.Two point charges $+1\mu\text{C}$ and $+5\mu\text{C}$ are placed at a distance. What is the ratio of the forces acting on them?
Ans: $1:1$ (By Newton's Third Law, forces are equal and opposite).
24.Match the physical quantities to their standard SI values:
Ans: (a) $\rightarrow$ (ii) $9 \times 10^9 \text{ Nm}^2/\text{C}^2$
(b) $\rightarrow$ (iii) $8.854 \times 10^{-12} \text{ C}^2/\text{Nm}^2$
(c) $\rightarrow$ (i) Vector sum of individual forces
25.The SI unit of electric field intensity is ____________ or $\text{V/m}$.
Ans: Newton/Coulomb ($\text{N/C}$)
26.The electric field inside a hollow conducting charged sphere is perfectly ____________.
Ans: Zero
27.Electric field lines always diverge away from a ____________ charge.
Ans: Positive
28.The magnitude of the electric field due to a point charge varies with distance $r$ as:
Ans: (B) $1/r^2$
29.Two electric field lines can intersect:
Ans: (C) never (intersecting lines would imply two directions of electric field at one point, which is impossible).
30.By convention, an electrostatic test charge is always taken as:
Ans: (A) Unit positive
31.Define electric field intensity at a point.
Ans: It is the electrostatic force experienced per unit positive test charge placed at that point ($\vec{E} = \vec{F}/q_0$).
32.Write the formula for the electric field due to a point charge $Q$ at a distance $r$.
Ans: $E = \frac{1}{4\pi\epsilon_0} \frac{|Q|}{r^2}$
33.Define electric field lines.
Ans: Imaginary curves drawn such that the tangent at any point gives the direction of the net electric field vector at that point.
34.Give the primary reason why electrostatic field lines do not form closed continuous loops.
Ans: Because electrostatic fields are conservative in nature (work done in a closed loop is zero).
35.What does the tangent drawn at any point on an electric field line represent?
Ans: The direction of the electric field intensity at that specific point.
36.Match the electric field concepts:
Ans: (a) $\rightarrow$ (ii) Parallel and equally spaced straight lines
(b) $\rightarrow$ (iii) Gives the direction of electric field vector
(c) $\rightarrow$ (i) Net electric field intensity is zero
37.The formula for electric flux through an area $\vec{A}$ in a uniform field $\vec{E}$ is $\Phi = $ ____________.
Ans: $\vec{E} \cdot \vec{A}$ or $EA \cos\theta$
38.The SI unit of electric dipole moment is ____________.
Ans: Coulomb-meter ($\text{C m}$)
39.The net electric flux passing through a closed cubic box enclosing an electric dipole is:
Ans: (C) Zero (Net charge of a dipole is $+q - q = 0$).
40.The torque acting on a dipole placed in a uniform electric field is maximum when the angle is:
Ans: (C) $90^\circ$ ($\tau = pE \sin\theta$, max when $\sin 90^\circ = 1$).
41.For a short dipole, the ratio of electric field magnitudes at an axial point to an equatorial point is:
Ans: (B) $2:1$
42.Define electric flux. Is it a scalar or a vector quantity?
Ans: The total number of electric field lines crossing normally through an area. It is a scalar quantity.
43.Define electric dipole moment. State its direction convention.
Ans: Product of magnitude of either charge and distance between them ($p = q \times 2a$). Directed from negative to positive charge.
44.Write the vector expression for the torque experienced by a dipole in a uniform electric field.
Ans: $\vec{\tau} = \vec{p} \times \vec{E}$
45.Under what condition is an electric dipole in stable equilibrium in a uniform electric field?
Ans: When dipole moment $\vec{p}$ is parallel to electric field $\vec{E}$ ($\theta = 0^\circ$).
46.Write the formula for the potential energy of a dipole placed in a uniform electric field.
Ans: $U = -\vec{p} \cdot \vec{E} = -pE \cos\theta$
47.Match the dipole formulas:
Ans: (a) $\rightarrow$ (iii) $\vec{p} \times \vec{E}$
(b) $\rightarrow$ (i) $-\vec{p} \cdot \vec{E}$
(c) $\rightarrow$ (ii) $q(2\vec{a})$
48.The surface charge density $\sigma$ is defined as charge per unit ____________.
Ans: Area
49.Gauss's law mathematically links the total electric flux to the total enclosed ____________.
Ans: charge
50.What is the standard SI unit of linear charge density ($\lambda$)?
Ans: (C) $\text{C/m}$
51.According to Gauss's Law, the electric flux out of a closed surface depends solely on:
Ans: (C) the net charge enclosed
52.A Gaussian surface is essentially:
Ans: (B) An imaginary closed surface
53.Define volume charge density ($\rho$) and write its SI unit.
Ans: Charge distributed per unit volume ($\rho = q/V$). SI unit is $\text{C/m}^3$.
54.State Gauss’s Law in electrostatics.
Ans: Total electric flux passing through a closed surface is $1/\epsilon_0$ times the total net charge enclosed by that surface.
55.Write the integral mathematical expression for Gauss’s Law.
Ans: $\oint \vec{E} \cdot d\vec{A} = \frac{q_{in}}{\epsilon_0}$
56.If a point charge $q$ is located at the center of a sphere, what happens to flux if radius is doubled?
Ans: It remains unchanged (flux only depends on enclosed charge, not on geometry).
57.If a closed surface contains zero net charge, what can be said about the net electric flux?
Ans: The net electric flux is zero.
58.Match the charge density symbols to their expressions:
Ans: (a) $\rightarrow$ (iii) $Q/L$
(b) $\rightarrow$ (i) $Q/A$
(c) $\rightarrow$ (ii) $Q/V$
59.The magnitude of the electric field due to an infinitely long straight charged wire is proportional to ____________.
Ans: $1/r$ (inversely proportional to distance)
60.The electric field produced by an infinite uniformly charged plane sheet is completely ____________ of the distance from the sheet.
Ans: independent
61.What is the electric field at a point inside a uniformly charged thin spherical shell?
Ans: (C) Zero
62.The electric field intensity due to a uniformly charged infinite plane sheet having surface density $\sigma$ is:
Ans: (B) $\sigma / 2\epsilon_0$
63.For a uniformly charged spherical shell, the electric field for points outside ($r > R$) behaves as if:
Ans: (C) The entire charge is concentrated at the center.
64.Write the final formula for the electric field due to an infinite line charge.
Ans: $E = \frac{\lambda}{2\pi\epsilon_0 r}$
65.Write the formula for the electric field just outside a charged conducting surface.
Ans: $E = \frac{\sigma}{\epsilon_0}$
66.Write the formula for the electric field at a distance $r$ ($r > R$) outside a spherical shell.
Ans: $E = \frac{1}{4\pi\epsilon_0} \frac{Q}{r^2}$
67.If two large parallel conducting plates carry equal and opposite surface charge densities ($\pm\sigma$), what is the electric field between them?
Ans: $E = \frac{\sigma}{\epsilon_0}$
68.Match the continuous charge distributions with their corresponding Electric Field magnitudes:
Ans: (a) $\rightarrow$ (iii) $\lambda / (2\pi\epsilon_0 r)$
(b) $\rightarrow$ (ii) $\sigma / (2\epsilon_0)$
(c) $\rightarrow$ (i) Zero
