Class 8th Chapter 13 of Science Questions & Answers

Multiple Choice Questions

—1. Choose the correct answer. Sound can travel through

(a) gases only

(b) solids only

(c) liquids only

(d) solids, liquids and gases.

—2. Voice of which of the following is likely to have minimum frequency?

(a) Baby girl

(b) Baby boy

c) A man

(d) A woman

FILL IN THE BLANKS

—(a) Time taken by an object to complete one oscillation is called __________.

—TIME PERIOD

—(b) Loudness is determined by the __________ of vibration.

—AMPLITUDE

—(c) The unit of frequency is __________

—HERTZ (HZ)

—(d) Unwanted sound is called __________ .

—NOISE

—(e) The shrillness of a sound is determined by the __________ of vibration.

—FREQUENCY

Question 1. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency

Solution:-

—Frequency = Total number of oscillations/ Second

—Frequency = 40/4 ( to obtain oscillations/ Second)

—= 10 Hz

—Time period is the time taken to complete one oscillation. It is also the inverse of frequency.

—Time period = 1/ Oscillating frequency

—= 1/10

—= 0.1 s

—∴ frequency = 10 Hz

—Time period = 0.1 s

True 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)

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