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.
Resolving power = 1/(1.22λ/2NA). It depends on wavelength and numerical aperture (NA = n×sin(θ))
Q.10Medium
When white light passes through a prism, violet light deviates more than red light. This is because:
Answer: D
Higher frequency → higher refractive index → slower speed in medium → greater deviation. All statements are correct.
Q.11Medium
An object is placed 10 cm from a concave lens of focal length 20 cm. Find the magnification.
Answer: C
Using lens formula: 1/(-20) = 101 + 1/v. v = -6.67 cm. Magnification m = -v/u = 6.1067 = 0.67
Q.12Medium
Polarization of light proves that light is:
Answer: B
Only transverse waves can be polarized. Polarization demonstrates the transverse nature of electromagnetic waves.
Q.13Easy
A thin lens has power +5 diopters. Find its focal length.
Answer: A
Power P = 1/f. f = 51 = 0.2 m = 20 cm. Positive power indicates convex lens.
Q.14Hard
In Young's double slit experiment, if one slit is covered with a transparent film of thickness t and refractive index μ, the path difference changes by:
Answer: A
Optical path = μt, geometrical path = t. Additional path difference = μt - t = (μ-1)t
Q.15Medium
The intensity at a point in the interference pattern of two coherent sources is I₁ and I₂. The resultant intensity is maximum when the phase difference is:
Answer: B
Maximum intensity occurs for constructive interference when phase difference = 0 or 2π. I_max = (√I₁ + √I₂)²
Q.16Hard
When a convex lens is immersed in water (n=34), its focal length compared to air is:
Answer: A
Lens maker's formula: 1/f = (n_lens/n_medium - 1)(1/R₁ - 1/R₂). When medium changes from air to water, (n_lens/n_medium) decreases, so f increases.
Q.17Hard
The minimum deviation through a prism occurs when:
Answer: D
All three conditions are equivalent and occur at minimum deviation: symmetric path, equal angles, and ray parallel to base.
Q.18Hard
The Brewster angle for glass-air interface (n_glass = 1.5) is approximately:
Answer: C
tan(θ_B) = n = 1.5. θ_B = arctan(1.5) = 56.31°. At this angle, reflected light is completely polarized.
Q.19Easy
A ray of light travels from medium 1 (refractive index n₁ = 1.5) to medium 2 (refractive index n₂ = 1.0). If the angle of incidence is 30°, what is the angle of refraction?
Answer: A
Using Snell's law: n₁sin(θ₁) = n₂sin(θ₂). So 1.5 × sin(30°) = 1.0 × sin(θ₂). This gives sin(θ₂) = 0.75, therefore θ₂ = 48.6°
Q.20Easy
A concave mirror produces a real, inverted, and magnified image. Where is the object located?
Answer: A
For a concave mirror, when object is between F and C, the image is real, inverted, and magnified. This is the magnification region used in shaving mirrors.
