Chapter 17 Electric Field

Chapter 0 Significant FiguresMr. Chong Kwai Kun

Significant FiguresSignificant figuresThere are 2 kinds of numbers:Exact numbers: Known with certainty.Measured numbers: weight, heightanything MEASURED. No measurement is perfect.

Significant figuresWhen a measurement is recorded only those digits that are dependable are written down.If you measured the width of a paper with your ruler you might record 21.7cm.To a mathematician 21.70, or 21.700 is the same. But to a scientist 21.7cm and 21.70cm is NOT the same.

21.700cm to a scientist means the measurement is accurate to within one thousandth of a cm.If you used an ordinary ruler, the smallest marking is the mm, so your measurement has to be recorded as 21.7cm.Rule: All digits are significant starting with the first non-zero digit on the left.

1st Exception to rule: In whole numbers that end in zero, the zeros at the end are not significant.

Significant figures2nd Exception to rule: If zeros are at the end of a number that has a decimal, the zeros are significant. How many sig figs?7400.50.000037 x 1057,000,000111111How many sig figs here?1.2210056.764.000.07927,083,000,000224334How many sig figs here?340121002100.05.000.004128,000,050,000425336Calculations with sig figs?Rule 1: When adding or subtracting measured numbers, the answer can have no more places after the decimal than the LEAST of the measured numbers.Rule 2: When Multiplying or dividing measured numbers, the answer can have no more significant figures than the least reliable measurement.Add/Subtract2.45cm + 1.2cm = 3.65cm, Round off to = 3.7cm

7.432cm + 2cm = 9.432Round to 9cmMultiply/Divide56.78 cm x 2.45cm = 139.111 cm2Round to 139cm2

75.8cm x 9.6cm = ?730 cm2The End

Question 11) How many significant figures are there in the following number: 1.200 109? a)4b)3c)2d)1e)Cannot deduce from given information.

Question 22) How many significant figures are in the measurement 1.3000 meters?threefourtwofive

Question 33) How many significant figures are there in the following summation:a)2b)3c)4d)5e)6

6.220 1.0 + 125 .Question 44) How many significant figures are there in the result of the following multiplication: (2.54) x (6.2) x (12.000)a)2b)3c)4d)5e)6

Question 55) Solve: 345.009 g - 23.009 g = ? 322 g322.000 g322.00 g322.0 g

Question 66) Solve: 13.004 m + 3.09 m + 112.947 m = ?a) 129 mb) 129.0 mc) 129.041 md) 129.04 mQuestion 77) How many significant figures should be expressed in the answer to the following:2.333x103 + 1.1x102 =1 2 34 Question 88) How many significant figures should be shown for the calculation? a)1b)2c)3d)4e)5

Question 99) A piece of stone has a mass of 24.595 grams and a volume of 5.34 cm3. What is the density of the stone? (remember that density = m/v) 0.217 cm3/g4.61 g/cm30.22 cm3/g4.606 g/cm3Question 1010) The mass of a watch glass was measured four times. The masses were 99.997 g, 100.008 g, 100.011 g, and 100.005 g. What is the average mass of the watch glass? 100.005 g100.00525 g100.0 g100.01 gQuestion 1111) Select the best answer to the calculation:(27.6 - 25.1)(3.000)7.50 7.500 7.5 8