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Explain the propagation of sound in air.
Define External respiration and internal respiration. Draw neat and labelled
diagram of Respiratory system.
Write the natural or man-made raw material of the following items,
Mattress, beaker, bangle, chair, gunny bag, broom, knife, pen
State the laws of reflection of light.
.
nd covered surface are of eft cylinder if
tsradius is 14cm and height lo con
cuse formula coverd surfa searea=2560h)
GENERAL SCIENCE DIGEST : STANDARD VIII
Answers
respiratory system of human
1) Propagation of sound in air
sound waves are longitudinal waves, and when they propagate compressions and rarefactions are formed.
The traveling of sound is called propagation of sound. Sound cannot propagate in the absence of a medium. The place where there is no air or air is removed, is called vacuum. Sound does not propagate (travels) through vacuum.
Sound travels through solid, liquid and gas.
We usually hear sound which comes to us through air.
Aquatic animals communicate as sound travels through water also.
We hear the sound through ear
2) EXTERNAL RESPIRATION
External respiration is the exchange of gases with the external environment, and occurs in the alveoli of the lungs.
INTERNAL RESPIRATION
Internal respiration is the exchange of gases with the internal environment, and occurs in the tissues.
3.) laws of reflection
According to laws of reflection,
1) the incident ray, reflected ray and normal to the reflecting surface are all coplanar( ie.lie in the same plane.)
2) the angle of incidence is equal to the angle of reflection
i = r
