Sound Solved Examples (Class 9 Physics)
Explore sound wave calculations including frequency, wavelength, speed, and Doppler effect. These problems develop understanding of sound propagation in di
TL;DR: Explore sound wave calculations including frequency, wavelength, speed, and Doppler effect. These problems develop understanding of sound propagation…
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Explore sound wave calculations including frequency, wavelength, speed, and Doppler effect. These problems develop understanding of sound propagation in di
Sound — Solved Numerical Examples (Step by Step)
Example 1: A sound wave has a frequency of 440 Hz and travels in air with a speed of 330 m/s. Calculate its wavelength.
Solution: Using the wave equation: v = fλ
λ = v / f
λ = 330 / 440
λ = 0.75 m
Example 2: A source of sound has a frequency of 100 Hz. If the wavelength in water is 15 m, what is the speed of sound in water?
Solution: Using v = fλ
v = 100 × 15
v = 1500 m/s
Example 3: The speed of sound in air is 330 m/s. How long will sound take to travel 1.65 km?
Solution: Distance = 1.65 km = 1650 m
Time = Distance / Speed
t = 1650 / 330
t = 5 s
Example 4: A tuning fork vibrates 250 times per second. What is its frequency and period?
Solution: Frequency f = 250 Hz
Period T = 1/f = 1/250 = 0.004 s
Example 5: An observer hears sound from a source 2 seconds after a light flash. If speed of light is 3 × 10^8 m/s and speed of sound is 330 m/s, what is the distance to the source?
Solution: Light travels almost instantly (arrives at time ≈ 0)
Sound takes 2 seconds to travel
Distance = Speed of sound × Time = 330 × 2 = 660 m
Example 6: A sound wave travels from air into water. The frequency remains 400 Hz. If the wavelength in air is 0.825 m and in water is 3.6 m, find the speeds in both media.
Solution: Speed in air v_air = f × λ_air = 400 × 0.825 = 330 m/s
Speed in water v_water = f × λ_water = 400 × 3.6 = 1440 m/s
Tips
- Frequency remains constant when a wave travels from one medium to another, but wavelength and speed change.
- Speed of sound depends on the medium: v_air = 330 m/s, v_water = 1500 m/s, v_steel = 5000 m/s.
- The relationship v = fλ is fundamental: if you know any two quantities, you can find the third.
Frequently Asked Questions
Why does sound travel faster in solids than in gases?
Particles in solids are closer together and bonded more tightly, so vibrations transfer more quickly from one atom to the next.
What is the difference between loudness and intensity of sound?
Intensity is the physical measure of power per unit area (W/m²), while loudness is the subjective perception of how loud the sound seems to our ears.
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