Physics is where JEE ranks are usually won or lost, since a single conceptual slip changes the whole answer. Questions here span mechanics, rotational motion, thermodynamics, waves and oscillations, electrostatics, current electricity, magnetism, optics, and modern physics. Numerical problems carry full derivations so you can see which step you skipped, not just which option was right.
A magnetic dipole of moment M is placed in a uniform magnetic field B. The torque experienced by the dipole when it makes an angle θ with the field is:
Answer: A
Torque on a magnetic dipole: τ = M × B = MB sin θ, where θ is the angle between M and B.
Q.422Easy
The magnetic field intensity at a distance r from a long straight current-carrying wire is:
Answer: B
Using Ampere's circuital law for an infinite straight wire: B = μ₀I/(2πr), where μ₀ = 4π × 10⁻⁷ T·m/A
Q.423Easy
A proton moving with velocity v perpendicular to a magnetic field B follows a circular path. The radius of this path is:
Answer: A
For circular motion in magnetic field: qvB = mv²/r, therefore r = mv/(qB)
Q.424Easy
Two parallel wires carrying currents I₁ and I₂ in the same direction, separated by distance d. The force per unit length between them is:
Answer: C
Magnetic force per unit length between parallel wires: F/L = μ₀I₁I₂/(2πd), attractive for same direction currents
Q.425Easy
A charged particle with charge q and mass m moves in a magnetic field. The cyclotron frequency is:
Answer: A
Cyclotron frequency: f = qB/(2πm) = ω/(2π), where ω = qB/m is the angular frequency
Q.426Medium
A rectangular coil of area A and N turns is rotated in a uniform magnetic field B with angular velocity ω. The maximum induced EMF is:
Answer: A
Maximum EMF in rotating coil: ε_max = NABω, where Φ = NBA cos(ωt), so ε = dΦ/dt = NABω sin(ωt)
Q.427Medium
A solenoid of length L and cross-sectional area A has N turns. Its self-inductance is:
Answer: A
Self-inductance of solenoid: L = μ₀n²V = μ₀(N/L)²AL = μ₀N²A/L
Q.428Medium
A conducting rod of mass m slides on two parallel rails separated by distance d in a magnetic field B perpendicular to the plane. If the rod moves with constant velocity v, the magnetic force on it is:
Answer: B
Induced EMF: ε = Bdv, induced current: I = Bdv/R, magnetic force: F = BId = B²d²v/R (opposes motion)
Q.429Easy
The magnetic moment of a current loop carrying current I with area A is:
Answer: A
Magnetic moment of a current loop: μ = IA, where I is current and A is area of the loop
Q.430Medium
A bar magnet is cut into two equal halves perpendicular to its length. The magnetic moment of each half is:
Answer: A
When cut perpendicular to length, magnetic moment is halved. Each piece has half the pole strength or length.
Q.431Medium
The mutual inductance between two coils depends on:
Answer: A
Mutual inductance M₁₂ = k√(L₁L₂) depends on coil geometry, orientation, and proximity, not on current or resistance
Q.432Medium
An electron (charge -e) and a proton (charge +e) move perpendicular to the same uniform magnetic field with the same velocity. The ratio of their radii of curvature is:
Answer: B
r = mv/(eB), so r_e/r_p = (m_e/m_p) = 18361 approximately
Q.433Hard
A magnetic field B is applied perpendicular to a conductor carrying current I. The Hall coefficient is related to:
Answer: A
Hall coefficient R_H = 1/(ne), where n is charge carrier density and e is elementary charge
Q.434Easy
A transformer has primary coil with N₁ turns and secondary coil with N₂ turns. The voltage ratio is:
Answer: A
Transformer equation: V₂/V₁ = N₂/N₁ (ideal transformer with no losses)
Q.435Medium
When a conductor moves through a magnetic field, an EMF is induced. This is due to the Lorentz force on:
Answer: A
Motional EMF arises because free electrons experience Lorentz force F = -e(v × B) as conductor moves through field
Q.436Medium
A paramagnetic material placed in a magnetic field becomes magnetized. This is because:
Answer: A
In paramagnetic materials, unpaired electrons have permanent magnetic moments that align with external field
Q.437Medium
An inductor with inductance L and a resistor with resistance R are connected in series with a DC source. The time constant is:
Answer: A
For LR circuit, time constant τ = L/R. Current rises as I = (V/R)(1 - e^(-t/τ))
Q.438Hard
A charged particle enters a uniform magnetic field region at an angle θ to the field direction. Its trajectory is:
Answer: A
Velocity component parallel to B is unaffected; perpendicular component causes circular motion, resulting in helical trajectory
Q.439Medium
The energy stored in a magnetic field of an inductor carrying current I is:
Answer: A
Energy stored in inductor: U = ½LI², derived from dW = LI dI integrated from 0 to I
Q.440Hard
A superconductor exhibits the Meissner effect, which means:
Answer: A
Meissner effect: superconductor actively expels magnetic flux from its interior (B = 0), not just zero resistance
