Physics Waves and Optics 2 — Questions and Answers
Question 1: A wave travels from a medium where its speed is 300 m/s into a medium where its speed is 200 m/s. How does the wavelength change?
- It increases by 50%
- It decreases by one-third (Correct answer)
- It stays the same
- It doubles
Correct answer: It decreases by one-third
Since frequency is constant at a boundary, wavelength is proportional to wave speed, so it decreases by the same ratio (200/300 = 2/3).
Question 2: Which phenomenon causes a swimming pool to appear shallower than it actually is?
- Reflection
- Diffraction
- Refraction (Correct answer)
- Interference
Correct answer: Refraction
Refraction bends light as it exits the water, making objects appear closer to the surface than they are.
Question 3: Two speakers emit sound waves of the same frequency in phase. At a point where the path length difference is 1.5 wavelengths, what occurs?
- Constructive interference
- Destructive interference (Correct answer)
- No interference
- Resonance
Correct answer: Destructive interference
A path difference of 1.5λ (a half-integer multiple) means the waves arrive out of phase, causing destructive interference.
Question 4: The speed of light in glass is 2.0 × 10⁸ m/s. What is the index of refraction of the glass?
- 1.0
- 1.5 (Correct answer)
- 2.0
- 0.67
Correct answer: 1.5
n = c/v = (3.0 × 10⁸)/(2.0 × 10⁸) = 1.5.
Question 5: A longitudinal wave is characterized by particles oscillating in what direction relative to wave propagation?
- Perpendicular
- At 45°
- Parallel (Correct answer)
- In circles
Correct answer: Parallel
In longitudinal waves, particle displacement is parallel (along) the direction of wave travel, forming compressions and rarefactions.
Question 6: Which color of visible light has the highest frequency?
- Red
- Green
- Yellow
- Violet (Correct answer)
Correct answer: Violet
Violet light has the shortest wavelength and therefore the highest frequency in the visible spectrum.
Question 7: A concave mirror has a focal length of 10 cm. Where must an object be placed to produce a real, inverted image the same size as the object?
- At the focal point
- At 10 cm
- At 20 cm (Correct answer)
- At 5 cm
Correct answer: At 20 cm
Placing the object at the center of curvature (2f = 20 cm) produces a real, inverted image of the same size at the same distance.
Physics Waves and Optics 2
A wave travels from a medium where its speed is 300 m/s into a medium where its speed is 200 m/s.
How does the wavelength change?