NEET Physics 3 — Questions and Answers
Question 1: When light travels from a denser medium to a rarer medium at an angle greater than the critical angle, what phenomenon occurs?
- Total internal reflection (Correct answer)
- Refraction
- Diffraction
- Polarization
Correct answer: Total internal reflection
Total internal reflection occurs when light strikes the interface at an angle exceeding the critical angle while traveling from denser to rarer medium.
Question 2: A convex lens of focal length 20 cm forms a real image of an object placed 30 cm from the lens. The image distance is:
- 60 cm (Correct answer)
- 30 cm
- 20 cm
- 15 cm
Correct answer: 60 cm
Using lens formula 1/v − 1/u = 1/f: 1/v = 1/20 + 1/(−30) = 1/60, so v = 60 cm.
Question 3: In Young's double slit experiment, if the distance between the slits is halved and the distance to the screen is doubled, the fringe width becomes:
- 4 times (Correct answer)
- 2 times
- Half
- Same
Correct answer: 4 times
Fringe width β = λD/d; when d is halved and D is doubled, β becomes 4 times the original.
Question 4: The energy of a photon with wavelength λ is E. If the wavelength is doubled, the energy becomes:
- E/2 (Correct answer)
- 2E
- E/4
- 4E
Correct answer: E/2
Since E = hc/λ, doubling wavelength halves the energy to E/2.
Question 5: Which colour of visible light has the highest frequency?
- Violet (Correct answer)
- Red
- Green
- Yellow
Correct answer: Violet
Violet light has the shortest wavelength (~400 nm) in the visible spectrum and therefore the highest frequency.
Question 6: The phenomenon responsible for the blue colour of the sky is:
- Rayleigh scattering (Correct answer)
- Mie scattering
- Total internal reflection
- Dispersion
Correct answer: Rayleigh scattering
Rayleigh scattering causes molecules to scatter blue light (shorter wavelength) much more strongly than red, making the sky appear blue.
Question 7: A ray of light passes through an equilateral prism at minimum deviation. The angle of incidence is approximately:
- 60° (Correct answer)
- 30°
- 45°
- 90°
Correct answer: 60°
For an equilateral prism (A = 60°) at minimum deviation, the ray passes symmetrically and the angle of incidence equals approximately 60°.
NEET Physics 3
When light travels from a denser medium to a rarer medium at an angle greater than the critical angle, what phenomenon occurs?