10 JUNIOR GRADE SCIENCE 



Ratio of the diameter of a circle to its circumference. When 

 the results of careful experiments on the diameters of circles and their 

 respective circumferences are collected and plotted on squared paper 

 it is found that all the points lie on a straight line passing through 

 the origin. This shows that the circumferences increase in size at the 

 same rate as the corresponding diameters. For example, from the 

 graph it is seen that a circle having a diameter of 5 cm. has a circum- 

 ference of 15'7 cm., while a circle with a diameter of 10 cm. has a 

 circumference of 31 '4 cm., or, when the diameter is doubled, the 

 circumference is also doubled. From the last figure it is evident that 

 a circle with a diameter of 1 cm. would have a circumference of 3*14 

 cm. Accurate measurements show that the circumference of any circle 

 is equal to 3'1416 times its diameter. 



QUESTIONS ON CHAPTERS I. AND II. 



1. Explain how you have found the length of a centimetre in inches, 

 and the length of an inch in centimetres. 



2. Describe three methods you have used in measuring the lengths of 

 curved lines and state how any two of them may be adapted to finding the 

 length of a winding road. 



3. The centres of two wheels are 12 feet apart, and the diameter of each 

 wheel is 15 inches. Find the least length of belt inch thick which will 

 pass right round the wheels. 



4. Describe any methods for measuring lines which are not straight. 

 Show how the principles of these methods may be used for large distances. 



5. What do you understand by parallel blocks ? Give two examples 

 of measurements for which such apparatus may be used. Point out the 

 likely sources of error in making the measurements and explain how you 

 would guard against them. 



6. The wheel of a certain bicycle revolves 800 times in running a mile. 

 What is the diameter of the wheel ? 



