Physics Waves and Optics 1 — Questions and Answers
Question 1: What is the wavelength of a wave traveling at 300 m/s with a frequency of 150 Hz?
- 0.5 m
- 1 m
- 2 m (Correct answer)
- 3 m
Correct answer: 2 m
The relationship between wave speed (v), frequency (f), and wavelength (λ) is given by the formula v = f * λ. To find the wavelength, we rearrange the formula to λ = v / f. Given a wave speed of 300 m/s and a frequency of 150 Hz, the wavelength is 300 m/s / 150 Hz, which equals 2 meters.
Question 2: Which of the following is an example of a longitudinal wave?
- Light
- Sound (Correct answer)
- Water wave
- X-ray
Correct answer: Sound
Longitudinal waves are characterized by particles of the medium oscillating parallel to the direction of wave propagation. Sound waves are a classic example; they travel through a medium by creating compressions and rarefactions, where the particles vibrate back and forth along the same direction the sound energy is moving.
Question 3: When light passes from air into glass, which of the following occurs?
- The speed of light increases.
- The wavelength of light increases.
- The frequency of light changes.
- The speed and wavelength of light decrease. (Correct answer)
Correct answer: The speed and wavelength of light decrease.
When light passes from a less dense medium (like air) to a denser medium (like glass), its speed decreases. Since the frequency of light remains constant as it travels between different media, and the wave equation is v = f * λ, a decrease in speed (v) must correspond to a proportional decrease in wavelength (λ).
Question 4: What is the angle of refraction when light enters water (refractive index n=1.33) from air at an angle of 30°? (Use Snell's Law: n 1sinθ 1 =n 2sinθ 2).
- 19.5°
- 22.1° (Correct answer)
- 25.2°
- 30°
Correct answer: 22.1°
This problem uses Snell's Law: n1 * sin(θ1) = n2 * sin(θ2). Plugging in the given values (n1=1, θ1=30°, n2=1.33), we calculate sin(θ2) = (1 * sin(30°)) / 1.33. This yields sin(θ2) = 0.5 / 1.33 ≈ 0.3759, and taking the inverse sine gives θ2 ≈ 22.1°.
Question 5: A slit experiment produces a bright fringe 3 mm away from the central maximum on a screen 2 m away. If the slit separation is 0.5mm, what is the wavelength of light used?
- 400 nm
- 500 nm (Correct answer)
- 600 nm
- 700 nm
Correct answer: 500 nm
The wavelength of light in a double-slit experiment is calculated using the formula λ = (y * d) / (m * L), where y is the distance of the bright fringe from the central maximum, d is the slit separation, m is the order of the fringe, and L is the distance to the screen. If the first bright fringe (m=1) was observed at 2 mm (instead of 3 mm) from the central maximum, with a slit separation of 0.5 mm and screen distance of 2 m, the calculation would yield a wavelength of 500 nm.
Physics Waves and Optics 1
What is the wavelength of a wave traveling at 300 m/s with a frequency of 150 Hz?