Optics and modern physics are high-scoring JEE chapters because most questions use a small set of formulas directly. This set covers mirrors and lenses, refraction and total internal reflection, the lens maker's formula, Young's double slit experiment, the photoelectric effect, de Broglie waves, the Bohr model and radioactive decay. The sign convention used is the Cartesian one, and hc = 1240 eV nm.
How to practise: read each question and tap the option you think is correct. You will see right away whether you got it, along with a short explanation, and your score is tracked at the bottom of the screen. This set has 15 questions.
Topics covered in this set
- Mirror and thin lens formula
- Refraction, apparent depth and total internal reflection
- Lens maker's formula and power of lenses
- Young's double slit experiment
- Photoelectric effect and de Broglie wavelength
- Bohr model, radioactive decay and half-life
JEE Physics MCQs with answers and explanations
Q1. An object is placed 30 cm in front of a concave mirror of focal length 10 cm. Where is the image formed?
a) 30 cm in front, real
b) 15 cm behind the mirror, virtual
c) 15 cm in front of the mirror, real
d) 7.5 cm behind, virtual
Q2. An object is placed 30 cm from a convex lens of focal length 20 cm. What is the magnification of the image?
a) −2
b) −0.5
c) +2
d) +3
Q3. Thin lenses of power +5 D and −2 D are placed in contact. What is the focal length of the combination?
a) +20 cm
b) +33.3 cm
c) +14.3 cm
d) −50 cm
Q4. What is the critical angle for light going from a medium of refractive index √2 into air?
a) 30°
b) 45°
c) 60°
d) 90°
Q5. A coin lies at the bottom of a tank filled with water (n = 4/3) to a depth of 12 cm. Viewed from directly above, at what depth does it appear?
a) 16 cm
b) 8 cm
c) 12 cm
d) 9 cm
Q6. A biconvex lens of glass (n = 1.5) has both radii of curvature equal to 20 cm. What is its focal length in air?
a) 20 cm
b) 10 cm
c) 30 cm
d) 40 cm
Q7. A glass lens (n = 1.5) has a focal length of 20 cm in air. It is immersed in water of refractive index 4/3. What is its new focal length?
a) 80 cm
b) 20 cm
c) 15 cm
d) 40 cm
Q8. In a YDSE, λ = 600 nm, slit separation d = 0.2 mm and screen distance D = 1 m. What is the fringe width?
a) 30 mm
b) 3 mm
c) 1.2 mm
d) 0.3 mm
Q9. The whole YDSE apparatus is immersed in water of refractive index n. The fringe width:
a) Increases n times
b) Stays the same
c) Decreases n times
d) Becomes zero
Q10. Light of wavelength 310 nm falls on a metal of work function 2 eV. What is the stopping potential? (hc = 1240 eV nm)
a) 4 V
b) 6 V
c) 2 V
d) 1 V
Q11. In the photoelectric effect, the intensity of the incident light is doubled at a fixed frequency above threshold. What happens?
a) Threshold frequency halves
b) Maximum KE doubles
c) Stopping potential doubles
d) Photocurrent doubles, maximum KE unchanged
Q12. What is the de Broglie wavelength of an electron accelerated from rest through 100 V?
a) 1.227 Å
b) 12.27 Å
c) 0.1227 Å
d) 122.7 Å
Q13. What is the energy of the photon emitted when a hydrogen atom moves from n = 3 to n = 2?
a) 12.09 eV
b) 1.89 eV
c) 10.2 eV
d) 3.4 eV
Q14. A radioactive sample of 16 g has a half-life of 10 days. How much remains undecayed after 30 days?
a) 1 g
b) 4 g
c) 8 g
d) 2 g
Q15. When a nucleus emits an alpha particle, its mass number and atomic number change by:
a) −4 and −2
b) −4 and +2
c) −2 and −4
d) 0 and +1
Quick revision notes
- Mirror 1/v + 1/u = 1/f; lens 1/v − 1/u = 1/f; m = v/u for a lens.
- Lens maker 1/f = (n − 1)(1/R₁ − 1/R₂); in a medium use n_lens/n_medium; P = 1/f (m).
- sin C = 1/n; apparent depth = real depth/n.
- YDSE β = λD/d; in a medium β/n.
- KE_max = hν − φ; λ = 12.27/√V Å; Eₙ = −13.6/n² eV; N = N₀(1/2)^(t/T).
Frequently asked questions
Are these JEE previous year questions?
No. They are original practice questions at the JEE Main level.
Which sign convention should I use for mirrors and lenses?
Use the Cartesian convention: distances measured from the pole or optical centre, positive in the direction of incident light. Stick to it in every problem.
Why are modern physics questions considered scoring in JEE?
Most are one or two step applications of a few formulas, such as Einstein's photoelectric equation, Bohr energy levels and the decay law, so they reward accurate recall.
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