Light of wavelength 500 nm in vacuum enters a medium of refractive index 1.5. The wavelength in the medium is:
Answer: A
Wavelength in medium = λ_vacuum / n = 1500.5 = 333.3 nm. Frequency remains constant in different media.
Q.202Easy
A concave mirror of focal length 20 cm forms a real, inverted, and magnified image. The object must be placed:
Answer: C
For magnified real image in concave mirror, object distance u must be between f and 2f (between focus and center of curvature), giving magnification m > 1.
Q.203Easy
Critical angle for a medium is 45°. Its refractive index is:
The rest mass energy of an electron is approximately:
Answer: A
Using E=mc², the rest mass energy of electron (m=9.11×10⁻³¹ kg) is 0.511 MeV, a fundamental constant in modern physics.
Q.208Easy
The de Broglie wavelength of a particle is given by:
Answer: A
de Broglie proposed that λ = h/p, where h is Planck's constant and p is momentum. This is fundamental to wave-particle duality.
Q.209Easy
The binding energy per nucleon is maximum for:
Answer: A
Iron-56 has the maximum binding energy per nucleon (~8.8 MeV/nucleon), making it the most stable nucleus. This is a key concept in nuclear physics.
Q.210Easy
A radioactive nucleus has half-life of 10 days. After 30 days, the fraction of original nuclei remaining is:
Answer: C
Number of half-lives = 1030 = 3. Remaining fraction = (21)³ = 81
Q.211Easy
Compton scattering demonstrates:
Answer: B
Compton scattering shows that photons behave as particles with momentum, providing evidence for particle nature of light. Wavelength shift Δλ = (h/mₑc)(1 - cosθ).
Q.212Easy
The energy of a photon in terms of wavelength is:
Answer: A
Since c = fλ, we have f = c/λ. Therefore E = hf = hc/λ
Q.213Easy
In the Bohr model, the radius of nth orbit in a hydrogen atom is proportional to:
Answer: B
rₙ = n²a₀, where a₀ is Bohr radius (0.53 Å). Orbital radius is proportional to n².
Q.214Easy
The ratio of specific charge (e/m) for an α-particle to that of a proton is:
Answer: A
α-particle: charge = 2e, mass = 4u. Proton: charge = e, mass = u. (e/m)ₐ/(e/m)ₚ = (2e/4u)/(e/u) = 21
Q.215Easy
A photon of energy 13.6 eV ionizes a hydrogen atom in its ground state. What is the kinetic energy of the ejected electron?
Answer: A
Ionization energy of hydrogen = 13.6 eV. A photon with exactly 13.6 eV provides just enough energy to ionize, leaving zero kinetic energy for the electron.
Q.216Easy
Which of the following correctly represents the order of penetrating power of nuclear radiations?
Answer: B
Gamma rays have the highest penetrating power due to their high energy and lack of charge. Beta particles have moderate penetrating power. Alpha particles have the lowest penetrating power.
Q.217Easy
The binding energy per nucleon of ²⁵⁶Fe (Z=26) is 8.8 MeV. The total binding energy of this nucleus is approximately:
Answer: A
Total binding energy = (Binding energy per nucleon) × (Mass number) = 8.8 × 256 ≈ 2253 MeV ≈ 2250 MeV.
Q.218Easy
A nucleus undergoes beta-minus decay. Which of the following is correct?
Answer: B
In beta-minus decay, a neutron converts to a proton, so atomic number (Z) increases by 1. Mass number (A) remains unchanged.
Q.219Easy
The angular momentum of an electron in the Bohr model is quantized as:
Answer: A
In Bohr's model, angular momentum is quantized as L = mₑvr = nℏ, where n = 1, 2, 3... and ℏ = h/2π.
Q.220Easy
In a nuclear reaction, ¹⁴₇N + ⁴₂He → ¹⁷₈O + ?. The missing particle is:
Answer: B
Conservation of mass number: 14 + 4 = 17 + A → A = 1. Conservation of atomic number: 7 + 2 = 8 + Z → Z = 1. But Z = 0 for neutron. Correction: 7 + 2 = 8 + Z → Z = 1, which is a proton. But mass number gives 18 = 17 + 1. Need neutron.
