# ICSE Class 9 Answered

**With the help of the example explain how will you do measurements**

Measurement is the process of comparing a given physical quantity with a known standard quantity of the same nature.

Measurement of time period of a simple pendulum:

(i) To measure the time period of a simple pendulum, the bob is slightly displaced from its mean position and is then released. This gives a to and fro motion about the mean position to the pendulum.

(ii) The time 't' for 20 complete oscillations is measured with the help of a stop watch.

(iii)Time period 'T' can be found by dividing 't' by 20.

To find the time period, the time for the number of oscillations more than 1 is noted because the least count of stop watch is either 1 s or 0.5 s. It cannot record the time period in fractions such as 1.2 or 1.4 and so on.

Measureing samll lengths using Vernier Callipers: -

Vernier caliper is an instrument used for measuring small lengths of solid objects where an ordinary scale cannot be applied. We can measure the length accurately up to the order of 10^{-2} cm, 10^{-3} cm depending upon the vernier used. Therefore a vernier caliper is important to measure the fraction of a smallest division of a measuring scale which otherwise could not be done by the judgment of the eye.

Measuring the diameter of a wire with the help of a screw gauge.

Following procedure is used to measure the diameter of a wire

(a). Calculate the least count and zero error of the screw gauge.

(b). Place the wire in between the studs. Turn the ratchet clockwise so as to hold the wire gently in between the studs. Record the main scale reading.

(c). Now record the division of circular scale that coincides with the base line of main scale. This circular scale division multiplied by least count will give circular scale reading.

(d). The observed diameter is obtained by adding the circular scale reading to the main scale reading. Subtract the zero error if any, with its proper sign, from the observed diameter to get the true diameter.