Page 111 - Physics - XI

Q8. How does surface tension vary with temperature?
Ans. The surface tension of a liquid decreases with rise· in temperature.

Q9. What is a capillary tube?
Ans. It is a tube with very fi ne bore.
Q10. Defi ne capillarity.
Ans. The phenomenon of rise or fall of a liquid in a capillary tube is called capillarity.

Q11. Why do we prefer fresh tap water rather than pure distilled water for the determination of
surface tension?
Ans. Distilled water is slightly greasy and value of surface tension may be aff ected by it.

Q12. What happens if the capillary tube is inclined?
Ans. Rise of liquid will be less.

Q13. Suppose the length of the capillary tube taken is less than the height upto which the liquid
could rise. What do you expect if such a tube is inserted inside the liquid? Explain your answer.
(NCERT)
Ans. If the length of the capillary tube taken is less than the height, then the liquid will rise up to the upper
edge of the capillary tube. Then, its surface will become less covered and becomes plane.
1
Thus, the radius of curvature increases, h ∝ as R → ∞ then h → 0
R
Q14. Two matchsticks are fl oating parallel and quite close to each other. What would happen if a
drop of soap solution or a drop of hot water falls between the two sticks? Explain your answer.
(NCERT)
Ans. When a drop of soap solution or a drop of hot water is made to fall between the two matchsticks
fl oating parallel and close to each other, then the force per unit length between the two matchsticks
decreases due to the decrease in the surface tension and the force on the farther end of both the
matchsticks get increased due to which they both will fl ow away from each other.

EXPERIMENT - 5

Aim
To determine the coeffi cient of viscosity of a given viscous liquid by measuring terminal velocity of a given
spherical body.

Apparatus and Materials Required
A long glass cylinder of length one metre and diameter 5 cm, rubber cork, a small glass tube of 0.5 to 1.0 cm
internal diameter, steel balls of diff erent sizes, stopwatch, metre scale, thermometer, glycerine, screw gauge,
plumb line, rubber bands, and clamp stand

Principle/Theory
Viscosity

The property of a fl uid by virtue of which an opposing force comes into play whenever there is a relative
motion between diff erent layers of fl uid (liquid or gas) is called viscosity.

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