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Sound is an essential part of our daily lives. From the chirping of birds to the music we enjoy, sound helps us communicate and understand our environment. But what exactly is sound? At its core, sound is a type of mechanical wave that travels through a medium such as air, water, or solids. Unlike light, sound cannot travel through a vacuum because it needs particles to vibrate and carry the wave forward.
In this chapter, we will explore the fundamental nature of sound, how it travels, and the key properties that define it. Understanding these concepts is crucial not only for science exams like the JPSC CCE but also for appreciating the physics behind everyday sounds.
Sound is produced when an object vibrates, causing the surrounding particles of the medium to vibrate as well. These vibrations travel in the form of waves, which our ears detect as sound. Since sound requires a medium to propagate, it is called a mechanical wave.
Sound waves are longitudinal waves. This means the particles of the medium vibrate back and forth in the same direction as the wave travels. Imagine pushing and pulling a slinky along its length - the coils compress and stretch in the direction of your push, creating regions of compression and rarefaction.
In air, these compressions are areas where air particles are close together, and rarefactions are where they are spread apart. The wave moves forward as these compressions and rarefactions travel through the air.
When a sound source vibrates, it pushes and pulls the particles of the medium, creating a chain reaction of vibrations. These vibrations travel outward in all directions as a wave. The speed and quality of sound depend on the medium it travels through.
For example, sound travels faster in solids like steel than in air because particles in solids are closer together and transmit vibrations more quickly.
Two important properties of sound waves are frequency and amplitude. These properties determine how we perceive sound in terms of pitch and loudness.
Frequency is the number of vibrations or cycles a sound wave completes in one second. It is measured in Hertz (Hz). For example, if a sound wave vibrates 100 times in one second, its frequency is 100 Hz.
The frequency of a sound wave determines its pitch. High-frequency sounds have a high pitch (like a whistle), while low-frequency sounds have a low pitch (like a drum beat).
Amplitude is the maximum displacement of particles from their rest position during vibration. It relates to the energy of the wave and determines the loudness of the sound. Larger amplitude means a louder sound, while smaller amplitude means a softer sound.
Wavelength, denoted by the Greek letter lambda (λ), is the distance between two consecutive compressions or rarefactions in a sound wave. It is measured in meters (m). Wavelength is inversely related to frequency - higher frequency means shorter wavelength, and vice versa.
The speed of sound is the distance traveled by a sound wave per unit time. It depends on the medium and conditions like temperature and humidity.
At room temperature (20°C), the speed of sound in air is approximately 343 meters per second (m/s). However, this speed changes with temperature and the type of medium.
| Medium | Speed of Sound (m/s) |
|---|---|
| Air (20°C) | 343 |
| Water (25°C) | 1497 |
| Steel | 5960 |
Step 1: Identify the temperature \( T = 25^\circ C \).
Step 2: Substitute into the formula:
\[ v = 331 + 0.6 \times 25 = 331 + 15 = 346 \, \text{m/s} \]
Answer: The speed of sound at 25°C is 346 m/s.
Step 1: Use the wave speed relation:
\[ v = f \times \lambda \]
Step 2: Rearrange to find wavelength \( \lambda \):
\[ \lambda = \frac{v}{f} \]
Step 3: Substitute values:
\[ \lambda = \frac{344}{512} = 0.672 \, \text{m} \]
Answer: The wavelength is 0.672 meters.
Step 1: Calculate speed at 20°C:
\[ v_1 = 331 + 0.6 \times 20 = 331 + 12 = 343 \, \text{m/s} \]
Step 2: Calculate speed at 30°C:
\[ v_2 = 331 + 0.6 \times 30 = 331 + 18 = 349 \, \text{m/s} \]
Step 3: Find the increase:
\[ \Delta v = v_2 - v_1 = 349 - 343 = 6 \, \text{m/s} \]
Answer: Speed of sound increases by 6 m/s when temperature rises from 20°C to 30°C.
Step 1: Recall frequency ranges:
Step 2: Classify each sound:
Answer: 15 Hz is infrasonic, 5000 Hz is audible, and 25,000 Hz is ultrasonic.
Step 1: Use the Doppler effect formula for source moving towards observer:
\[ f' = f \times \frac{v}{v - v_s} \]
where:
Step 2: Substitute values:
\[ f' = 1000 \times \frac{340}{340 - 30} = 1000 \times \frac{340}{310} \approx 1096.77 \, \text{Hz} \]
Answer: The observer hears a frequency of approximately 1097 Hz.
When to use: Quickly estimate speed of sound at different temperatures without complex calculations.
When to use: Solving numerical problems involving wave properties.
When to use: Frequency shift problems in exams.
When to use: Objective questions on sound classification.
When to use: Explaining or recalling the nature of sound waves.
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