Page 32 - Physics - XI

Q11. What should be measured most accurately to fi nd the radius of curvature?
Ans. l since it occurs as a squared term in

l 2 h
R = +
6 h 2
Q12. Is there any instrument based upon the principle of a spherometer and used to measure focal
length of the lens directly?
Ans. Yes, it is called a dioptometer.

Q13. What is the main precaution in a spherometer experiment?
Ans. We rotate the circular scale in the same direction only to avoid backlash error.

Q14. Why are good spherometers made of gun metal?
Ans. To minimise wear and tear

Q15. Does a given object, say concave mirror or a convex mirror, have same radius of curvature for
its two surfaces? (NCERT)
Ans. No, because in a concave mirror or a convex mirror, the polished plane surface has infi nite radius of
curvature.

EXPERIMENT - 5

Aim

To determine the mass of two diff erent objects using a beam balance.

Apparatus and Materials Required

A physical balance, a weight box with a set of milligram masses, forceps, two objects whose masses are to
be determined, and spirit level

Description of Apparatus (Physical Balance)

A physical balance is a device that measures the weight (or gravitational mass) of an object by comparing
it with a standard weight (or standard gravitational mass).
Rigid beam
B 1 C B B 2

E 1 T E E
S 1 X 1 Plate T X 2 S 2 2

Pillar Plumb
V line
Pointer
P P R P
1 2
G N
A 1 G V Pans A 2

W Weight box
W 1 K W 2
Levelling screws

Fig. 5.1: A physical balance and a weight box.
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