# NCERT Class 11 Physics Solutions: Chapter 2-Unit and Measurement Part 7

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Question: 2.11

The length, breadth and thickness of a rectangular sheet of metal are 4.234 m, 1.005 m and 2.01 cm respectively. Give the area and volume of the sheet to correct significant figures.

• Length of sheet,

• Thickness of sheet,

• Rules for determining significant figures

The given table lists the respective significant figures:

 Quantity Number Significant Figure l 4.234 4 b 1.005 4 h 2.01 3
• Hence, area and volume both must have least significant figures i.e. 3.

• Surface area of the sheet

• Volume of the sheet

• This number has only 3 significant figures i.e. 8, 5 and 5.

Question: 2.12

The mass of a box measured by a grocer’s balance is 2.300 kg. Two gold pieces of masses 20.15 g and 20.17 g are added to the box. What is

(a) The total mass of the box,

(b) The difference in the masses of the pieces to correct significant figures?

• Mass of grocer’s box = 2.300 kg

• Mass of gold piece I = 20.15 g = 0.02015 kg

• Mass of gold piece II = 20.17 g = 0.02017 kg

• (a) The total mass of the box

Total mass of the box

• In addition, the final result should retain as many decimal places as there are in the number with the least decimal places. Hence, the total mass of the box is 2.3 kg. Rounded off to two significant figures as mass of box has two significant figure only.

• (b) The difference in the masses of the pieces to correct significant figures

• Difference in masses of the pieces

• In subtraction, the final result should retain as many decimal places as there are in the number with the least decimal places.