Give reasons for the following statements.

(a) A standard system of units was accepted.

(b) The correct position of eye is important to take measurements.

(c) A tailor uses measuring tape to take measurements.

(d) Jerks should be given to a clinical thermometer before using.

(e) Labs prefer using electronic balances.

(a) In earlier times, people used non-standard methods of measurement. These methods were approximate and often varied from the actual values. To avoid confusion and to maintain uniformity, scientists all over the world accepted a set of standard units of measurement. These units are definite, exact, convenient, and remain the same everywhere.

(b) For taking measurements, the eye must be placed exactly vertical above the mark to be read. The correct position of the eye is very important because, in other positions, the reading appears either more or less than the actual value. Such an error caused by the wrong positioning of the eye is called parallax error.

(c) A tailor uses measuring tape because :

• It can measure long objects.
• It is flexible and is made of a ribbon of cloth, plastic or metal strip.
• It can be easily carried.
• It can be used to measure around curves or corners of objects.
• Like a ruler, a measuring tape is also available in various lengths such as 1 m, 2 m, 5 m, 10 m and 50 m.

(d) When the bulb of the thermometer is in contact with a body, the mercury expands and rises in the tube. After the thermometer is removed, the mercury near the bulb contracts, but the mercury in the tube stays separated at the kink. This keeps the level of mercury constant. By giving jerks before reuse, all the mercury is brought back near the bulb, which ensures accurate measurement.

(e) Labs prefer using electronic balances for scientific purposes where accurate measurements are required. Scientific work needs highly sensitive instruments that can measure with a high degree of accuracy. Electronic balances can measure the mass of even very small objects up to grams and milligrams. They also give readings instantly. Hence, they are accurate, reliable, and convenient to use.