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.
In a cyclotron, a charged particle spirals outward as it gains energy. The frequency of revolution is independent of:
Answer: B
The cyclotron frequency f = qB/(2πm) is independent of velocity. As velocity increases, radius increases but period remains constant (independent of v).
Q.202Medium
A rectangular conducting loop is partially inside a uniform magnetic field region. If the loop is pulled out with constant velocity v, the induced EMF depends on:
Answer: A
EMF induced ε = BLv where L is the length of the conductor cutting magnetic field lines and v is the velocity. It depends on all three factors: B, L, and v.
Q.203Medium
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.204Medium
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.205Medium
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.206Medium
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.207Medium
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.208Medium
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.209Medium
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.210Medium
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.211Medium
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.212Medium
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.213Medium
The self-inductance of a solenoid depends on:
Answer: A
L = μ₀n²AL, where n = N/l. Self-inductance depends on geometry and material properties, not on current.
Q.214Medium
A charged particle moves in a helical path in a uniform magnetic field. This happens when the particle's velocity has:
Answer: A
Perpendicular component causes circular motion, parallel component causes linear motion, resulting in helical path
Q.215Medium
In a Hall effect experiment with a rectangular conductor in a magnetic field, the Hall voltage is proportional to:
Answer: A
Hall voltage V_H = (1/ne) × (IB/t), proportional to B and I, inversely proportional to carrier concentration n
Q.216Medium
A rectangular loop is placed in a non-uniform magnetic field. The loop will experience:
Answer: A
Non-uniform field causes net force on the loop due to unequal forces on different sides, plus torque due to magnetic moment
Q.217Medium
The energy density of a magnetic field is given by:
Answer: A
Magnetic energy density u = B²/(2μ₀), similar to electric field energy density
Q.218Medium
Two coils have self-inductances L₁ and L₂ with coupling coefficient k. Their mutual inductance is:
Answer: A
Mutual inductance M = k√(L₁L₂), where 0 ≤ k ≤ 1 is the coupling coefficient
Q.219Medium
A particle with charge q and mass m undergoes circular motion in a magnetic field. Its cyclotron frequency is independent of:
Answer: A
Cyclotron frequency f = qB/(2πm). It depends on q, B, and m, but not on velocity v
Q.220Medium
The magnetic field between the poles of a permanent magnet is approximately:
Answer: B
Between the parallel poles of a strong permanent magnet (in the central region), the magnetic field is approximately uniform. However, it becomes non-uniform near the pole edges.
