In Young's double slit experiment, if one slit is covered with a glass plate of thickness t and refractive index n, the central bright fringe shifts by:
An object is placed 15 cm in front of a concave mirror of radius of curvature 20 cm. The magnification is:
Answer: A
f = 10 cm, u = 15 cm. Using m = -v/u, first find v from mirror formula: v = uf/(u-f) = 5150 = 30 cm. m = -1530 = -2
Q.565Medium
Diffraction fringes are observed when light passes through a single slit. The first minimum occurs at angle θ where:
Answer: A
For single slit diffraction, first minimum occurs when path difference = λ, giving b sin θ = λ, or sin θ = λ/b where b is slit width.
Advertisement
Q.566Easy
When white light passes through a prism, violet light deviates more than red light because:
Answer: D
Violet has smaller λ, higher frequency, and the medium has higher n for violet (dispersion). All factors lead to greater deviation.
Q.567Easy
A lens of power -5 diopters is used to correct vision. This lens is:
Answer: B
Negative power indicates concave lens (f = -20 cm). Concave lens is used to correct myopia (short-sightedness).
Q.568Hard
In a diffraction grating with 5000 lines/cm, the second order spectrum is observed at angle 30°. The wavelength of light is:
Answer: B
d = 1/(5000×10^2) = 2×10^-6 m. Using d sin θ = mλ: 2×10^-6 × sin(30°) = 2 × λ. λ = 10^-56 = 200 nm
Q.569Hard
In a compound microscope, the objective has focal length 0.5 cm and eyepiece has focal length 5 cm. The distance between them is 20 cm. The magnifying power is approximately:
Answer: B
M = -(v₀/u₀) × (D/f_e) where v₀ ≈ L = 20 cm, u₀ ≈ f₀ for final image at infinity. M ≈ (020.5) × (525) = 40 × 5 = 200. For near point at lens: ~400.
Q.570Medium
Light is incident on a transparent glass slab at Brewster's angle. At this angle:
Answer: C
At Brewster's angle, tan θ_B = n, and reflected ray is perpendicular to refracted ray. This is the polarization angle.
Q.571Hard
A concave mirror forms a real image 4 times larger than the object. The object is placed at distance u from the mirror. The focal length is:
Answer: A
Magnification m = -4 (real, inverted). m = -v/u, so v = 4u. Using mirror formula: 1/f = 1/u + 41u = 45u, therefore f = 4u/5. Rechecking: f = u/3 when m=-3.
Q.572Easy
The resolving power of a microscope increases when:
In a Newton's rings experiment, dark fringe appears when the air gap thickness is:
Answer: A
Dark fringes occur at the center (t=0) and when 2t = mλ (m = 1,2,3...), giving constructive interference with phase change at glass surface.
Q.574Easy
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.575Hard
In photoelectric effect, the stopping potential V₀ for a metal is 2V. If the frequency of incident light is doubled, the new stopping potential will be:
Answer: D
Using hf = Φ + eV₀, when frequency doubles: h(2f) = Φ + eV'₀. Since V'₀ = (2hf - Φ)/e = 2(hf/e) - Φ/e = 2V₀ + hf/e - Φ/e, the increase is not exactly double due to work function dependency.
Q.576Easy
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.577Medium
An electron transitions from n=3 to n=1 in a hydrogen atom. The frequency of emitted photon is (Use Rydberg constant R = 1.097×10⁷ m⁻¹):
