# Case Study Questions for Class 11 Physics Chapter 2 Units and Measurements

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Case Study Questions

Question 1:

Measurement of Physical Quantity
All engineering phenomena deal with definite and measured quantities and so depend on the making of the measurement. We must be clear and precise in making these measurements. To make a measurement, magnitude of the physical quantity (unknown) is compared.
The record of a measurement consists of three parts, i.e. the dimension of the quantity, the unit which represents a standard quantity and a number which is the ratio of the measured quantity to the standard quantity.

(i) A device which is used for measurement of length to an accuracy of about 10-5m, is
(a) screw gauge
(b) spherometer
(c) vernier calipers
(d) Either (a) or (b)

(ii) Which of the technique is not used for measuring time intervals?
(a) Electrical oscillator
(b) Atomic clock
(c) Spring oscillator
(d) Decay of elementary particles

(iii) The mean length of an object is 5 cm. Which of the following measurements is most accurate?
(a) 4.9 cm
(b) 4.805 cm
(c) 5.25 cm
(d) 5.4 cm

(iv) If the length of rectangle l = 10.5 cm, breadth b = 2.1 cm and minimum possible measurement by scale = 0.1 cm, then the area is
(a) 22.0 cm2
(b) 21.0 cm2
(c) 22.5 cm2
(d) 21.5 cm2

(v) Age of the universe is about 1010 yr, whereas the mankind has existed for 106 yr. For how many seconds would the man have existed, if age of universe were 1 day?
(a) 9.2 s
(b) 10.2 s
(c) 8.6 s
(d) 10.5 s