UNIT NO.9
Waves and Energy
(Solved Exercise)
9.3 Answer the following questions.
1. How can you differentiate between longitudinal and transverse waves?
2. Why we consider sound waves as longitudinal waves?
3. Give examples of sounds that differ in
(1) loudness (2) pitch ?
4. What is meant by audible sound?
5. What is the audible frequency range of human?
6. What is the audible frequency range of a bat?
7. Which type of sounds are used in some emergency?
9.4. Constructed Response Questions
1. State some important uses of sounds.
Answer:
1. Communication: Sounds help us talk and understand each other. We use words and voices to share information and express feelings.
2. Warning Signals: Sounds like alarms and sirens alert us to danger. They keep us safe by letting us know when something is wrong.
3. Entertainment: We enjoy music, movies, and games because of sounds. They make these activities fun and interesting.
4. Nature Awareness: Birds chirping, water flowing, and wind rustling leaves are sounds in nature. They help us connect with the environment and understand the world around us.
2. How can you prove that animals or birds also communicate with one another?
Answer:
Observation: Scientists have observed animals making specific sounds in different situations, such as warning calls or mating calls.
Response: Animals often react to these sounds by changing their behavior. For example, they may gather in a group or flee from a potential threat.
Consistency: Certain sounds consistently convey specific messages among animals, showing a pattern of communication.
Research: Studies have used technology to record and analyze animal sounds, providing evidence of structured communication systems in various species.
3. Why we cannot hear the whistle of a bat?
Answer:
The whistle of a bat is at a frequency too high for human ears to detect. Bats use ultrasonic sounds, which means the waves are beyond the range of human hearing, typically above 20,000 Hertz. Since our ears are not sensitive to such high frequencies, we cannot hear the whistle of a bat. Bats use these ultrasonic sounds for echolocation, helping them navigate and find prey in the dark.
4. Why you can hear very weak sound easily in the night but not during the day?
Answer:
At night, the environment is generally quieter because there is less human activity and traffic. During the day, there are many sounds from various sources like traffic, people talking, and machines running. Additionally, during the night, the air is cooler and more stable, leading to less interference and distortion of sound waves. This allows weak sounds to travel more effectively and be heard more easily in the quiet nighttime environment.
5. The given wave is transverse in nature.
Identify and write the names for A, B, X and Y
Answer:
A: Trough
B: Crest
X: Amplitude
Y: Wavelength
6. For a transverse wave as shown in the Figure, Answer the following questions:
a. What is the amplitude of the wave?
Answer: 4cm
b. What is the wavelength of the wave?
Answer: 8cm