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 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.22Medium
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.23Medium
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.24Medium
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.25Medium
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.26Medium
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.27Medium
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.28Medium
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.29Medium
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.30Medium
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.31Medium
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.32Medium
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.33Medium
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.34Medium
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.35Medium
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.
Q.36Medium
A rectangular conducting loop ABCD with sides a and b is rotated with angular velocity ω in a uniform magnetic field B perpendicular to the plane of rotation. The induced EMF is:
Answer: B
When the loop rotates, the magnetic flux through it varies as Φ = BA·cosωt. The induced EMF = -dΦ/dt = BA·ω·sinωt = Bab·ω·sinωt
Q.37Medium
Two magnets are placed with their north poles facing each other. The force between them varies with distance r as:
Answer: D
Two magnetic dipoles interact with force F ∝ 1/r⁴ when aligned along the same axis. This is because the magnetic field of a dipole varies as 1/r³, and force on a dipole is proportional to the field gradient.
Q.38Medium
A conducting rod of length L moves with velocity v perpendicular to its length in a magnetic field B. The motional EMF induced is maximum when:
Answer: B
Motional EMF = B·L·v·sinθ, where θ is the angle between v and B. EMF is maximum when sinθ = 1, i.e., when v is perpendicular to B.
Q.39Medium
The magnetic susceptibility of a paramagnetic material is:
Answer: B
Paramagnetic materials have positive but small magnetic susceptibility (χ > 0, typically 10⁻⁵ to 10⁻³). Diamagnetic materials have small negative susceptibility, and ferromagnetic materials have large positive susceptibility.
Q.40Medium
A charged particle with charge q and mass m is moving with speed v in a circular path of radius r in a magnetic field. The magnetic field strength is:
Answer: A
From qvB = mv²/r (centripetal force equals magnetic force), we get B = mv/(qr). This is the relationship between field strength, particle properties, and circular path radius.
