Cite an experiment to show that sound needs a material medium for its propagation.
Take an electric bell and connect it to electrical supply. An airtight glass bell jar with a vacuum pump.
When we press the switch, we will be able to hear the bell. One can hear the sound of the ringing bell. Now, take a jar and make a small hole in the bottom and insert a small pipe though it. Connect the other end of the pipe to a vacuum cleaner. When the air in the jar is pumped out gradually, the sound becomes feeble although the same amount of current is flowing through the bell. It will be observed that the sound of the ringing bell decreases. When there is no air present inside, we will not be able to hear the sound of the bell. This shows that sound requires a medium for its propagation.
Explain the working and application of a sonar.
Explain how sound is produced by your school bell.
Explain how defects in a metal block can be detected using ultrasound.
Distinguish between loudness and intensity of sound.
A sound wave travels at a speed of 339 m s-1. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?
Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a dark room?
Which wave property determines
(a) loudness, (b) pitch?
A sonar device on a submarine sends out a signal and receives an echo 5 s later. Calculate the speed of sound in water if the distance of the object from the submarine is 3625 m.
Explain how the human ear works.
How is ultrasound used for cleaning?
Which of the following has more inertia: (a) a rubber ball and a stone of the same size? (b) a bicycle and a train? (c) a five-rupees coin and a one-rupee coin?
State the universal law of gravitation.
Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.
A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force (Fig. 11.3). Let us take it that the force acts on the object through the displacement. What is the work done in this case?
What is meant by a pure substance?
In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
What are canal rays?
State any two conditions essential for good health.
How is our atmosphere different from the atmospheres on Venus and Mars?
Who discovered cells, and how?
Differentiate between striated, unstriated and cardiac muscles on the basis of their structure and site/location in the body.
How do biotic and abiotic factors affect crop production?
A stone is thrown vertically upward with an initial velocity of 40 m/s. Taking g = 10 m/s2, find the maximum height reached by the stone. What is the net displacement and the total distance covered by the stone?
An electric heater is rated 1500 W. How much energy does it use in 10 hours?
What are the differences between amphibians and reptiles?
When a carpet is beaten with a stick, dust comes out of it. Explain.
Do you know of any activity which may be polluting this water source?
Suggest a method to liquefy atmospheric gases.
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Under what condition(s) is the magnitude of average velocity of an object equal to its average speed?