5.
A pendulum oscillates 40 times in 4 seconds. Find its time period and
frequency
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?
6.
7.
Identify the part which vibrates to produce sound in the following
instruments.
(a) Dholak
(b) Sitar
(c) Flute
8.
What is the difference between noise and music? Can music become noise
sometimes?
9.
List sources of noise pollution in your surroundings.
10.
Explain in what way noise pollution is harmful to human.
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.
12.
Sketch larynx and explain its function in your own words.
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?
Answers
Answer:
5. Frequency is defined as the number of oscillations per unit time.
Time = 4 sec.
Time Period = (Time taken) / (Number of Oscillations)
Time Period = (4/40) = 0.1 sec.
Frequency = (Number of Oscillations)/ (Time taken)Frequency = (40/4) =10Hz
6. Here, a mosquito vibrates its wings at an average rate of 500 vibrations per second.
Therefore, the frequency of the sound is 500 Hz.
Time period of the wave is defined as the reciprocal of the frequency of the wave.
Time Period = (Time Taken)/ (Number of Oscillations)
= (1/500) = 0.002 sec.
7. Identify the part which vibrates to produce sound in the following instruments.
(a) Dholak - stretched membranes
(b) Sitar - stretched strings
(c) Flute - air column
8. The type of sound which are unpleasant to listen is known as noise whereas music is a pleasant sound, which produces a sensation.
Yes, music can become noise when it’s too loud.
9. Following are the major sources of noise pollution:
- Sound of vehicles
- Sound of kitchen appliances
- Sound of bursting crackers
- Sound of loudspeakers, TV, transistors
10. Noise pollution causes:
(a) Lack of sleep
(b) Anxiety
(c) Hypertension
and these are harmful to health
11. I would suggest my parents buy a house three lanes away from the roadside because house on the roadside would be much noisy in both days and night due to running vehicles. Whereas, a house three lanes away would be comparatively quieter as the intensity of noise decreases with the distance between the source and the listener.
12. Larynx is also known as voice box. it is at the upper end of the windpipe. Two vocal cords are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for passage of air (fig. 13.12). When lung force air through the slit, the vocal cords vibrate, producing sound. muscles attached to the vocal cords can make the cords tight or loose.
When the vocal cords are tight and thin, the type or quality of voice is different from that when they are loose and thick.
13. The speed of light is more than that of the speed of sound. Thus, due to more speed of light it reaches us before sound. So, lightning is seen earlier and thunder is heard later.