Physics Waves and Optics 3 — Questions and Answers
Question 1: What is the critical angle for total internal reflection if the index of refraction of a medium is 1.5 (relative to air)?
- 30°
- 41.8° (Correct answer)
- 48.6°
- 60°
Correct answer: 41.8°
sin(θ_c) = 1/n = 1/1.5 = 0.667, so θ_c = arcsin(0.667) ≈ 41.8°.
Question 2: In a double-slit experiment, what happens to the fringe spacing if the distance between the slits is doubled?
- Fringe spacing doubles
- Fringe spacing is halved (Correct answer)
- Fringe spacing is unchanged
- Fringes disappear
Correct answer: Fringe spacing is halved
Fringe spacing Δy = λL/d; doubling d halves the spacing.
Question 3: A wave on a string has a frequency of 50 Hz and a wavelength of 0.4 m. What is its speed?
- 0.008 m/s
- 125 m/s
- 20 m/s (Correct answer)
- 50 m/s
Correct answer: 20 m/s
v = fλ = 50 Hz × 0.4 m = 20 m/s.
Question 4: Which type of electromagnetic wave has the longest wavelength?
- X-rays
- Ultraviolet
- Infrared
- Radio waves (Correct answer)
Correct answer: Radio waves
Radio waves occupy the lowest-frequency, longest-wavelength end of the electromagnetic spectrum.
Question 5: A diverging lens always produces images that are:
- Real and enlarged
- Virtual and upright (Correct answer)
- Real and inverted
- Virtual and inverted
Correct answer: Virtual and upright
A diverging (concave) lens always produces virtual, upright, and diminished images on the same side as the object.
Question 6: The Doppler effect causes the observed frequency of a source moving toward you to be:
- Lower than emitted frequency
- Equal to emitted frequency
- Higher than emitted frequency (Correct answer)
- Zero
Correct answer: Higher than emitted frequency
A source approaching an observer compresses wave fronts, increasing the observed frequency above the emitted value.
Question 7: Polarization is a property unique to which type of wave?
- Longitudinal waves only
- Transverse waves only (Correct answer)
- Both longitudinal and transverse
- Standing waves only
Correct answer: Transverse waves only
Only transverse waves can be polarized, because polarization restricts oscillation to a single plane perpendicular to propagation.
Physics Waves and Optics 3
What is the critical angle for total internal reflection if the index of refraction of a medium is 1.5 (relative to air)?