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 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.
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):
