Sound class 8 questions and answers: Science Class 8 chapter 10 question answer
| Textbook | Ncert |
| Class | Class 8 |
| Subject | Science |
| Chapter | Chapter 10 |
| Chapter Name | Sound ncert solutions |
| Category | Ncert Solutions |
| Medium | English |
Are you looking for Class 8 Science chapter 10 question answer? Now you can download ncert solutions for class 8 science chapter 10 pdf from here.
Question 1: Choose the correct answer.
Sound can travel through
(a) gases only
(b) solids only
(c) liquids only
(d) solids, liquids, and gases
Answer 1: (d) solids, liquids, and gases.
Question 2: Voice of which of the following is likely to have a minimum frequency?
(a) Baby girl
(b) Baby boy
(c) A man
(d) A woman
Answer 2: (c) A man
Question 3: In the following statements, tick ‘T’ against those which are true, and ‘F’ against those which are false.
(a) Sound cannot travel in vacuum. (T/F)
(b) The number of oscillations per second of a vibrating object is called its time period. (T/F)
(c) If the amplitude of vibration is large, sound is feeble. (T/F)
(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)
(e) The lower the frequency of vibration, the higher is the pitch. (T/F)
(f) Unwanted or unpleasant sound is termed as music. (T/F)
(g) Noise pollution may cause partial hearing impairment. (T/F)
Answer 3:
- True
- False
- False
- True
- False
- False
- True
Question 4: Fill in the blanks with suitable words.
(a) Time taken by an object to complete one oscillation is called _______.
(b) Loudness is determined by the _______ of vibration.
(c) The unit of frequency is _______.
(d) Unwanted sound is called _______ .
(e) Shrillness of a sound is determined by the _______ of vibration.
Answer 4:
- (a) Time taken by an object to complete one oscillation is called the time period.
- (b) Loudness is determined by the amplitude of vibration.
- (c) The unit of frequency is hertz.
- (d) Unwanted sound is called noise.
- (e) The shrillness of a sound is determined by the frequency of vibration.
Question 5: A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Answer 5: To find the time period and frequency of the pendulum, we use the following formulas:
- Frequency ( f ): The number of oscillations per second.
\(f = \frac{\text{Total oscillations}}{\text{Total time}}\)
Given:
Total oscillations = 40, Total time = 4 seconds
\(f = \frac{40}{4} = 10 \text{ Hz}\) - Time Period ( T ): The time taken for one complete oscillation.
\(T = \frac{1}{f}\)
\(T = \frac{1}{10} = 0.1 \text{ seconds}\)
- Frequency = 10 Hz
- Time Period = 0.1 seconds
Question 6: The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?
Answer 6: To find the time period ( T ) of the vibration, we use the formula:
\(T = \frac{1}{f}\)
where ( f ) is the frequency (number of vibrations per second).
Given:
- Frequency, ( f = 500 ) Hz
Calculation:
\(T = \frac{1}{500}\)
T = 0.002 seconds or 2 milliseconds
Time Period = 0.002 seconds (or 2 milliseconds)
Question 7: Identify the part which vibrates to produce sound in the following instruments.
(a) Dholak (b) Sitar (c) Flute
Answer 7: a) Dholak – It consists of a head which is a stretched membrane. Vibrations are set into these stretched strings. When the head is beaten gently, these vibrations produce sound, and thus Dholak produces sound.
b) Sitar – It is a musical instrument. Stretched strings are part of it. Vibrations are produced when the string is plucked when played. These vibrations produce sound, and thus sitar produces sound.
c) Flute – It’s an instrument which has holes in it. It is a hollow pipe. The air inside the pipe is set into vibration when air is blown over its mouth, and this produces a pleasant sound.
Question 8: What is the difference between noise and music? Can music become noise sometimes?
Answer 8: Noise is an unpleasant sound which is a result of irregular vibrations. Music is a sound which is pleasant to hear. Yes, music can sometimes become noise when it is played at very high volumes on loudspeakers.
Question 9: List sources of noise pollution in your surroundings.
Answer 9: Some sources of noise pollution are as follows:
- Televisions and transistors running at high volumes
- Loudspeakers and crackers
- Horns of buses, cars and trucks
- Home appliances such as mixer, desert cooler, etc.
Question 10: Explain in what way noise pollution is harmful to human.
Answer 10: Too much noise in our surroundings is known as noise pollution. It is very harmful to us and can cause irritability, loss of concentration, high blood pressure, headache, stress, sleep disturbances, etc. It can even damage hearing permanently.
Question 11: Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.
Answer 11: Purchasing a home three lanes from the roadside is preferable since the noise level will be lower than on the main road. Vehicles may be the source of the noises; the noise strength diminishes with increasing distance from the source to the listener. Therefore, purchasing a property that is three lanes away from the roadside is preferable.
Question 12: Sketch larynx and explain its function in your own words.
Answer 12: The larynx, also called the voice box, is a hollow, tube-like structure located in the throat. It connects the pharynx (throat) to the trachea (windpipe) and plays a crucial role in breathing, sound production, and protecting the airway. The larynx contains the vocal cords, which vibrate when air passes through them, producing sound.
The pitch and volume of our voice depend on the tension and movement of these cords. Additionally, the larynx has a flap-like structure called the epiglottis, which prevents food and liquids from entering the windpipe during swallowing. This helps keep the airway clear and prevents choking. Overall, the larynx is essential for speech, respiration, and airway protection.
Question 13: Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain why?
Answer 13: Yes! Lightning is seen earlier than thunder because light travels much faster than sound. The speed of light is about 300,000 km/s, while the speed of sound in air is only around 343 m/s. Since both occur at the same time, light reaches our eyes almost instantly, whereas sound takes more time to travel through the air, causing the delay in hearing thunder.
- Speed of Light: Light travels at a speed of approximately 300,000 km/s in air.
- Speed of Sound: Sound travels much slower, at about 343 m/s in air.