The potential at distance r from a point charge Q is V. If the distance is doubled, the new potential is:
Answer: A
Electric potential V = kQ/r is inversely proportional to distance. If r → 2r, then V → V/2.
Q.42Easy
A charged particle enters a uniform electric field perpendicularly. Its path is:
Answer: B
Similar to projectile motion, a charged particle in a perpendicular electric field experiences constant acceleration, resulting in a parabolic trajectory.
Q.43Easy
What is the capacitance of an isolated conducting sphere of radius R in vacuum?
Answer: A
The capacitance of an isolated conducting sphere is C = 4πε₀R = R/k, where k = 1/(4πε₀).
Q.44Easy
The energy stored in a capacitor of capacitance C charged to potential V is:
Answer: B
Energy stored in a capacitor is U = (21)CV² = (21)QV = Q²/(2C).
Q.45Hard
Two point charges Q and -Q are at distance 2d apart. The potential difference between two points on the perpendicular bisector at distances x and 2x from the midpoint is proportional to:
Answer: C
Using potential superposition and the dipole configuration, ΔV = 2kQd(1/x - 21x) for points on the perpendicular bisector.
Advertisement
Q.46Easy
A conductor of arbitrary shape carries charge Q. Which is constant throughout the conductor?
Answer: B
Inside and on the surface of a conductor in electrostatic equilibrium, the potential is constant everywhere.
Q.47Medium
The electric field just outside a conductor surface is perpendicular to the surface. This is because:
Answer: B
If there were a tangential component of electric field at the surface, charges would move tangentially, violating electrostatic equilibrium. Thus, only the normal component exists.
Q.48Easy
A parallel plate capacitor has plate area A, separation d, and dielectric constant K. Its capacitance is:
Answer: B
The capacitance of a parallel plate capacitor with dielectric is C = Kε₀A/d, where K is the dielectric constant.
Q.49Medium
Three capacitors of capacitance C each are connected in a combination where two are in parallel and this combination is in series with the third. The equivalent capacitance is:
Answer: B
Two capacitors C in parallel: C_parallel = 2C. This in series with C: C_eq = (2C × C)/(2C + C) = 2C/3.
Q.50Medium
A point charge is brought from infinity to a point in an electric field. Work done depends on:
Answer: C
Electric force is conservative; work depends only on initial and final positions (potentials), not on the path taken. W = q(V_initial - V_final).
Q.51Medium
A uniformly charged ring of radius R carries total charge Q. What is the electric field at a point on the axis at distance x from the center?
Answer: A
Using Coulomb's law and symmetry, the radial components cancel. The axial component gives E = kQx/(x² + R²)^(23).
Q.52Easy
Two identical conducting spheres carry charges +Q and -Q. When brought into contact, the charge on each sphere becomes:
Answer: A
When identical conductors touch, charge redistributes equally. Total charge = Q + (-Q) = 0, so each gets 0 charge.
Q.53Easy
A Gaussian surface encloses a net charge of 5 μC. The electric flux through the surface is:
An electric dipole of moment p is placed in a uniform electric field E at angle θ to the field. The potential energy is:
Answer: A
Potential energy of dipole in electric field: U = -p·E = -pE cos θ. Minimum at θ = 0 (aligned).
Q.55Medium
A non-conducting sphere of radius R is uniformly charged with charge density ρ. What is the electric field at distance r from center (r < R)?
Answer: A
Using Gauss's law with spherical symmetry: E(4πr²) = (ρ × 4πr³/3)/ε₀, giving E = ρr/(3ε₀).
Q.56Medium
The work done to move a charge q from point A (potential V_A) to point B (potential V_B) is:
Answer: B
Work done by external agent = q(V_B - V_A). If V_B > V_A, positive work is needed.
Q.57Medium
A parallel plate capacitor is filled partially with dielectric (dielectric constant K, thickness d/2) and partially with air (thickness d/2). Its capacitance is:
Answer: B
Capacitors in series: 1/C_total = d/(2ε₀AK) + d/(2ε₀A). Solving: C = 2ε₀AK/[d(K+1)].
Q.58Medium
An electron enters a uniform electric field of strength E with initial velocity perpendicular to the field. Its trajectory is:
Answer: B
Motion is analogous to projectile motion: uniform motion perpendicular to field, accelerated motion along field direction → parabola.
Q.59Medium
A conducting plane carries uniform surface charge density σ. The electric field just outside the surface is:
Answer: B
Using Gauss's law for an infinite charged plane: E = σ/ε₀ (one side only, applies just outside conductor).
Q.60Easy
Two capacitors C₁ and C₂ are connected in parallel across voltage V. The ratio of charges stored is:
Answer: A
In parallel: same voltage V. Q₁ = C₁V, Q₂ = C₂V. Therefore Q₁/Q₂ = C₁/C₂.
