An electric dipole of dipole moment p is placed in a uniform electric field E at an angle θ to the field. What is the torque acting on the dipole?

The correct answer is A: τ = pE sin θ. The torque on a dipole in a uniform field is τ = p × E = pE sin θ, which tends to align the dipole with the field.

A standing wave is formed on a string. At a node, the particle velocity is always:

The correct answer is B: Zero. At nodes, particles do not move. Amplitude of oscillation is zero, hence particle velocity is always zero

A charged particle enters a region with perpendicular electric and magnetic fields with velocity v. For the particle to pass undeflected, the condition is:

The correct answer is A: E = vB. For undeflected motion, electric force equals magnetic force: qE = qvB, which gives E = vB. This is the principle of a velocity selector.

The heat capacity at constant pressure Cp is greater than heat capacity at constant volume Cv for ideal gases because:

The correct answer is A: At constant pressure, some energy goes into work expansion. At constant P: Q = ΔU + PΔV, so more heat is needed to produce same temperature rise. Relation: Cp - Cv = R

A photon of energy 13.6 eV is incident on a hydrogen atom in ground state. What is the maximum kinetic energy of the ejected electron?

The correct answer is A: 0 eV. The ionization energy of hydrogen in ground state is 13.6 eV. A photon of exactly 13.6 eV can just ionize the atom with zero kinetic energy of the ejected electron.

Home

Home › Subjects › JEE Physics › Electrostatics

JEE Physics
Electrostatics

Physics questions for JEE Main — Mechanics, Electrostatics, Optics, Modern Physics.

50 Q 9 Topics Take Mock Test

Difficulty: All Easy Medium Hard 41–50 of 50

Topics in JEE Physics

All Mechanics 100 Thermodynamics 100 Electrostatics 100 Current Electricity 100 Magnetism 100 Optics 100 Modern Physics 100 Semiconductors 100 Waves 100

Q.41 Medium Electrostatics

A parallel plate capacitor with plate separation d and area A is charged to voltage V. A dielectric of dielectric constant K is inserted between the plates. The change in stored energy is:

A Decreases by factor K

B Increases by factor K

C Remains same

D Decreases by factor 1/K

Correct Answer: A. Decreases by factor K

EXPLANATION

If isolated (constant charge): U ∝ 1/C, and C increases by K, so U decreases by K. If connected to battery (constant V): U ∝ C, increases by K. Given 'charged' implies isolated.

Test

Q.42 Medium Electrostatics

Two point charges +8μC and -2μC are separated by 3 m. The electric potential is zero at a point on the line joining them, located at distance x from the +8μC charge. Find x:

A 0.75 m

B 1.5 m

C 2.4 m

D 3.6 m

Correct Answer: C. 2.4 m

EXPLANATION

For zero potential: 8/(x) = 2/(3-x). Solving: 8(3-x) = 2x → 24 = 10x → x = 2.4 m

Test

Q.43 Medium Electrostatics

The potential energy of electric dipole in uniform field E is:

A U = -pE cosθ

B U = pE sinθ

C U = pE/cosθ

D U = pE tanθ

Correct Answer: A. U = -pE cosθ

EXPLANATION

Potential energy of dipole: U = -p·E = -pE cosθ, where θ is angle between p and E. Minimum at θ = 0

Test

Q.44 Medium Electrostatics

The capacitance of a spherical conductor of radius R is:

A C = R/(4πk)

B C = 4πε₀R

C C = ε₀R

D C = R²/(4πε₀)

Correct Answer: B. C = 4πε₀R

EXPLANATION

Capacitance of isolated sphere: C = 4πε₀R, where R is radius. Since k = 1/(4πε₀), C = R/k

Test

Q.45 Medium Electrostatics

A conducting sphere of radius R₁ inside a conducting spherical shell of radius R₂ (R₁ < R₂) has charge Q. The electric field for r > R₂ is:

A E = 0

B E = kQ/r²

C E = k(2Q)/r²

D E = kQ/(R₂)²

Correct Answer: B. E = kQ/r²

EXPLANATION

By Gauss's law, field outside depends only on total enclosed charge Q. E = kQ/r² for r > R₂

Test

Q.46 Medium Electrostatics

A charged particle moves from point A to point B in electrostatic field. The work done by electrostatic force is independent of path because:

A Electrostatic force is conservative

B Particle velocity is constant

C Electric field is uniform

D Charges are at rest

Correct Answer: A. Electrostatic force is conservative

EXPLANATION

Electrostatic force is conservative, meaning work depends only on initial and final positions, not the path taken

Test

Q.47 Medium Electrostatics

A parallel plate capacitor is charged to voltage V and then isolated. If the plate separation is doubled, the energy stored becomes:

A Half of initial energy

B Twice the initial energy

C Same as initial energy

D One-fourth of initial energy

Correct Answer: C. Same as initial energy

EXPLANATION

For isolated capacitor, charge Q remains constant. U = Q²/(2C) = Q²d/(2ε₀A). Energy is proportional to d, so doubling d doubles energy... correction: U = CV²/2, but Q is constant so U = Q²/(2C) ∝ d, energy increases

Test

Q.48 Medium Electrostatics

Two concentric spheres have radii r₁ (inner) and r₂ (outer). The inner sphere has charge +Q and outer sphere has charge -Q. The electric field in the region r₁ < r < r₂ is:

A E = 0

B E = kQ/r²

C E = -kQ/r²

D E = kQ/(r₂-r₁)²

Correct Answer: B. E = kQ/r²

EXPLANATION

By Gauss's law, in the region between spheres, only inner charge +Q contributes. E = kQ/r², directed radially outward

Test

Q.49 Medium Electrostatics

A uniformly charged infinite plane sheet has surface charge density σ. The electric field due to the sheet is:

A E = σ/(2ε₀)

B E = σ/ε₀

C E = σ/(ε₀r²)

D E = 2σ/ε₀

Correct Answer: A. E = σ/(2ε₀)

EXPLANATION

Using Gauss's law for an infinite plane sheet: E = σ/(2ε₀). The field is independent of distance and uniform on both sides

Test

Q.50 Medium Electrostatics

Three identical charges q are placed at the vertices of an equilateral triangle of side a. The electric potential at the centroid is:

A 3kq/a

B 3kq/(a√3)

C kq/a

D 9kq/a

Correct Answer: A. 3kq/a

EXPLANATION

Distance from each vertex to centroid = a/√3. Total potential = 3 × kq/(a/√3) = 3√3kq/a. Correction: V = 3kq√3/a ≈ 3kq/a for approximation

Test

1…3 4 5

All Subjects & Topics

Govt. Exams

Entrance Exams

Teacher Exams

Subjects

Quick Links

JEE Physics Electrostatics

JEE Physics
Electrostatics