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 photoelectric effect, the stopping potential is 2V. The maximum kinetic energy of ejected electron is:
Answer: A
The stopping potential is related to maximum kinetic energy by: KE_max = eV_s. For V_s = 2V, KE_max = 2 eV.
Q.22Easy
A nucleus undergoes alpha decay. The mass number and atomic number of the daughter nucleus are:
Answer: A
In alpha decay, a nucleus emits ⁴₂He. Parent nucleus (A,Z) → Daughter (A-4, Z-2) + Alpha particle (4,2).
Q.23Easy
The activity of a radioactive sample is defined as:
Answer: B
Activity A = dN/dt = λN, measured in Becquerels (decays per second) or Curies. It represents the decay rate.
Q.24Easy
Which of the following statements about photoelectric effect is correct?
Answer: C
From Einstein's photoelectric equation: KE_max = hf - φ. As frequency increases, maximum kinetic energy increases proportionally. Stopping potential depends on frequency, KE depends on frequency (not intensity), and threshold frequency is directly related to work function.
Q.25Easy
In beta decay of ¹⁴₆C, the atomic number of daughter nucleus is:
Answer: B
In beta-minus decay, a neutron converts to a proton, emitting an electron and antineutrino. Atomic number increases by 1: Z = 6 + 1 = 7. The daughter nucleus is ¹⁴₇N.
Q.26Easy
The half-life of a radioactive substance is 10 days. What fraction of the original sample remains after 30 days?
Answer: C
After 30 days = 3 half-lives. Remaining fraction = (21)³ = 81
Q.27Easy
In Bohr's model, the angular momentum of electron in nth orbit is:
Answer: C
Bohr's quantization condition: L = mvr = n(h/2π) = nℏ, where n = 1, 2, 3...
Q.28Easy
The characteristic X-rays are produced when:
Answer: B
When fast electrons knock out inner shell (K-shell) electrons, electrons from outer shells fall down, emitting characteristic X-rays specific to the target material.
Q.29Easy
Which of the following statements about the photoelectric effect is correct?
Answer: B
Stopping potential Vs = (hf - W)/e, which depends directly on frequency. Intensity affects photocurrent, not maximum KE. Threshold frequency exists. Emission requires photon energy > work function.
Q.30Easy
In Bohr's model of hydrogen atom, the angular momentum of electron in the nth orbit is:
Answer: A
Bohr's quantization condition states that angular momentum L = mvr = nh/(2π), where n is the principal quantum number.
Q.31Easy
If the binding energy per nucleon of ⁵⁶Fe is 8.79 MeV and that of ²³⁵U is 7.59 MeV, which nucleus is more stable?
Answer: A
Higher binding energy per nucleon indicates greater nuclear stability. ⁵⁶Fe (8.79 MeV/nucleon) is more stable than ²³⁵U (7.59 MeV/nucleon).
Q.32Easy
A ²¹⁰₈₄Po nucleus undergoes alpha decay. The resulting nucleus is:
Answer: A
Alpha decay: A decreases by 4, Z decreases by 2. ²¹⁰₈₄Po → ²⁰⁶₈₂Pb + ⁴₂He. The resulting nucleus is Lead-206.
Q.33Easy
X-rays are produced when high-speed electrons strike a metal target. This is an example of:
Answer: B
Bremsstrahlung (braking radiation) occurs when fast electrons are decelerated by the nucleus, producing continuous X-ray spectrum.
Q.34Easy
The half-life of ¹⁴C is 5730 years. A sample contains 1 mg of ¹⁴C. After 11,460 years, the remaining mass will be:
Answer: A
11,460 years = 2 × 5730 years = 2 half-lives. After 2 half-lives: 1 × (21)² = 0.25 mg remains.
