Nuclear forces are strong forces that are attractive at normal nuclear distances (~1 fm) but become repulsive at very short distances (<0.5 fm), creating a potential well. They act between all nucleons (protons and neutrons).
Q.222Easy
The ionization energy of He⁺ (hydrogen-like ion) is:
Answer: C
For hydrogen-like ions: IE = 13.6 × Z² eV. For He⁺, Z = 2, so IE = 13.6 × 4 = 54.4 eV.
Q.223Easy
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?
Answer: A
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.
Q.224Easy
In the Bohr model, which of the following represents the radius of the nth orbit in a hydrogen atom?
Answer: A
The radius of nth orbit in hydrogen atom is given by rₙ = n²a₀/Z, where a₀ = 0.53 Å is the Bohr radius and Z is atomic number.
Q.225Easy
In beta decay, a neutron converts to a proton. Which particle is emitted?
Answer: B
In β⁻ decay, a neutron converts to proton, emitting electron and antineutrino: n → p + e⁻ + ν̄ₑ
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Q.226Easy
Which of the following statements about alpha particles is correct?
Answer: B
Alpha particles (⁴₂He) are helium nuclei containing 2 protons and 2 neutrons. They have low penetrating power but high ionizing power.
Q.227Easy
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.228Easy
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.229Easy
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.230Easy
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.231Easy
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.232Easy
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.233Easy
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.234Easy
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.235Easy
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.236Easy
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.237Easy
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.238Easy
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.239Easy
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.240Easy
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.
