Topic outline

    • Sound

      Q21. What is the length of the vocal cord in men and women?

      Ans. The vocal cords in men are about 20mm long. In women these are about 5mm shorter.


      Q22. What does the working of a toy telephone tell us about sound?

      Ans. The working of a toy telephone tells us that sound travels through solid substances.


      Q23. Who produces sound of higher pitch: a man or a woman? Why?

      Ans. Usually the voice of a woman has a higher frequency and therefore, produces a sound of higher pitch.  

      Q24. Name three characteristics which are used to describe oscillations.

      Ans. Frequency, amplitude and frequency are the three characteristics which are used to describe oscillations.


      Q25. What is musical sound? Give example.

      Ans. Musical sound is one which is pleasing to the ear. Sound produced by a harmonium is a musical sound.


      Q26. What is noise pollution?

      Ans. Presence of excessive or unwanted sounds in the environment is called noise pollution.


      Q27. What is amplitude of oscillation?

      Ans. The maximum displacement of a vibrating object from its central position is called the amplitude of oscillation.


      Q28. Why can ultrasound not be heard by humans?

      Ans. Ultrasound cannot be heard by humans because the ultrasound equipment works at frequencies higher than 20,000 Hz.


      Q29. Why a sound cannot be heard on the moon?

      Ans. A sound cannot be heard on the moon because on the moon there is no medium such as air though which the vibrations can propagate.

      Q30. Why should we not put a sharp, pointed or hard thing into our ears?

      Ans. We must never put a sharp, pointed or hard thing into our ear. It can damage the eardrum. The damaged eardrum can impair hearing.


      Q31. How is sound produced in mridangam?

      Ans. When we strike the membrane of a mridangam, the sound that we hear is not only that of the membrane but of the whole body of the instrument.


      Q32. What is the relation between 'time-period' and 'frequency' of an oscillating body?

      Ans. Time Period given by the inverse of the frequency.

      Time Period = 1/frequency


      Q33. What differences will you hear in a sound if there is an increase in (i) amplitude, and (ii) frequency?

      Ans. (i) The sound will become loud on increasing the amplitude.

      (ii) The sound will become shrill on increasing the frequency.


      Q34. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.

      Ans. Frequency = (Number of Oscillations)/Time = 40/4 = 10 Hz

      Time period = 1/(Frequency of Oscillation) = 1/10 = 0.1 sec

      Q35. 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?

      Ans. Speed of the light is more than the speed of sound. Thus, Lightning is seen earlier and thunder is heard later.


      Q36. Name one solid, one liquid and one gas through which sound can travel.

      Ans. Solid: Metal (Iron, Steel, Aluminium), wood, bricks etc.

      Liquid: Water

      Gas: Air


      Q37. Whose voice is more shriller: a baby or a woman?

      Ans. The voice of a baby has a higher frequency (or higher pitch) than that of a woman due to which the voice of a baby is even more shrill than that of a woman.


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