CHAPTER 3. Scientific Notation

Transcription

1 CHAPTER 3 Scientific Notation People who work in scientific fields often have to use very large and very small numbers. Look at some examples in the following table: Measurement Value Density of air at 27 C and 1 atm pressure g/cm 3 Radius of a calcium atom One light-year The mass of a neutron m km g You can see that measurements such as these would be awkward to write out repeatedly. Also, calculating with very long numbers is likely to lead to errors because it s so easy to miscount zeros and decimal places. To make these numbers easier to handle, scientists express them in a form known as scientific notation, which uses powers of 10 to reduce the number of zeros to a minimum. Look at a simple example of the way that scientific notation works. Following are some powers of 10 and their decimal equivalents Suppose we rewrite the values in the table using scientific notation. The numbers become much less cumbersome. Measurement Value Density of air at 27 C and 1 atm pressure g/cm 3 Radius of a calcium atom m One light-year km Mass of a neutron g 1 of 12

2 CONVERTING QUANTITIES TO SCIENTIFIC NOTATION General Plan for Converting Quantities to Scientific Notation Quantity expressed in long form Use the resulting number as the coefficient M. Move the decimal point right or left until there is only one nonzero digit to the left of it. Count the number of places the decimal point moved, and call that number n. Make the number n negative if the decimal moved to the right. M, the coefficient of 10 n n, the exponent of 10 Quantity expressed in the form M 10 n (scientific notation) SAMPLE PROBLEM 1 Express the following measurements in scientific notation. a L b kg SOLUTION 1. ANALYZE What is given in the problem? What are you asked to find? two measured quantities the measured quantities expressed in scientific notation 2 of 12

3 Items 2. PLAN What steps are needed to Move the decimal point in each rewrite the quantities in value until there is only one nonzero scientific notation? digit to the left of it. This number becomes the coefficient, M. Count the number of places the decimal was moved. If it moved to the left, the count is a positive number. If it moved to the right, the count is a negative number. Make this number, n, the exponent of 10. Quantity written in long form M 10 n 3. COMPUTE a. Express L in scientific notation Data Measured quantity L kg Quantity expressed in scientific notation? L? kg M 3.1 q L L b. Express kg in scientific notation. M 4.9 a b decimal point moves 5 places to the left n 5 decimal point moves 4 places to the right q n kg kg 4. EVALUATE a b Are units correct? Yes; the original Yes; the original measurement was measurement was in liters. in kilograms. Is the quantity correctly Yes; the decimal Yes; the decimal expressed? was moved to the was moved to the left five places to right four places give a coefficient to give a coeffiof 3.1 and an cient of 4.9 and an exponent of 5. exponent of 4. 3 of 12

4 PRACTICE 1. Express the following quantities in scientific notation: a m ans: m b kg ans: kg c kg/m 3 ans: kg/m 3 d Hz ans: Hz e amp ans: amp f km ans: km g L ans: L h g ans: g i kj/h ans: kj/h j m 2 ans: m 2 CALCULATING WITH QUANTITIES IN SCIENTIFIC NOTATION SAMPLE PROBLEM 2 What is the total of the measurements mm, mm, and mm? SOLUTION 1. ANALYZE What is given in the problem? What are you asked to find? three measured quantities expressed in scientific notation the sum of those quantities Items Data Measured quantity mm mm mm 2. PLAN What steps are needed to add the quantities? Convert each quantity so that each exponent is the same as that on the quantity with the largest exponent. The quantities can then be added together. Make sure the result has the correct number of significant figures. 4 of 12

5 (P 10 Q ) (R 10 S ) (T 10 V )? (P R T ) 10 Q? if the exponents are different, convert the quantities so that they have the same exponent as the term with the largest exponent add the quantities P, R, and T, and multiply them by the factor 10 Q (P 10 Q ) (R 10 Q ) (T 10 Q )? 3. COMPUTE mm mm mm? mm Convert the second and third quantities to multiples of To convert mm: mm M 10 4 mm Because one was added to the exponent, the decimal point must be moved one place to the left. M To convert mm: mm M 10 4 mm Because two was added to the exponent, the decimal point must be moved two places to the left. M Now the three quantities can be added, as follows: mm mm mm mm To express the result in the correct number of significant figures, note that the result should only contain two decimal places mm mm 4. EVALUATE Are the units correct? Is the quantity correctly expressed in scientific notation? this digit is 5, so round up Yes; units of all quantities were millimeters. Yes; there is only one number to the left of the decimal point. 5 of 12

6 Is the quantity expressed in the correct number of significant figures? Yes; the result was rounded to give two decimal places to match the least accurate measurement. PRACTICE 1. Carry out the following calculations. Express the results in scientific notation and with the correct number of significant figures. a km km km ans: km b m m m ans: m c m m m 3 ans: m 3 d mg mg mg ans: mg e atoms atoms atoms ans: atoms f nm nm nm ans: nm SAMPLE PROBLEM 3 Perform the following calculation, and express the result in scientific notation: cm cm SOLUTION 1. ANALYZE What is given in the problem? What are you asked to find? two quantities expressed in scientific notation the product of the two quantities Items Data Measured quantity cm cm 2. PLAN What steps are needed to multiply quantities expressed in scientific notation? Multiply the coefficients, and add the exponents. Then transform to the correct scientific notation form with the correct units and number of significant figures. 6 of 12

7 (P 10 Q ) (R 10 S ) Result correctly written in scientific notation, with the correct units and number of significant figures multiply the coefficients and add the exponents (P 10 Q ) unit 1 (R 10 S ) unit 2 coefficients exponents (P R) 10 (Q S) product of coefficients sum of exponents (Q S) product of units (P R) 10 (unit 1 unit 2) 3. COMPUTE cm cm ( ) 10 (4 2) (cm 2 cm) cm 3 To transform the result to the correct form for scientific notation, move the decimal point left one place and increase the exponent by one cm (6 1) cm cm 3 To express the result to the correct number of significant figures, note that both of the original quantities have three significant figures. Therefore, round off the result to three significant figures cm cm 3 if there is more or less than one nonzero digit to the left of the decimal, move the decimal and change the exponent to account for the move, then round to the correct number of significant figures 4. EVALUATE Are the units correct? this digit is 5, so round up Is the quantity expressed to the correct number of significant figures? Yes; the units cm 2 and cm are multiplied to give cm 3. Yes; the number of significant figures is correct because the data were given to three significant figures. 7 of 12

8 Yes; moving the decimal point de- creases the coefficient by a factor of 10, so the exponent increases by one to compensate. Is the quantity expressed correctly in scientific notation? PRACTICE 1. Carry out the following computations, and express the result in scientific notation: a cm cm ans: cm 2 b mm mm mm ans: mm 3 c m m m ans: m 3 d m m kg ans: kg m 2 e dm dm dm ans: dm 3 SAMPLE PROBLEM 4 Perform the following calculation, and express the result in scientific notation: g ml SOLUTION 1. ANALYZE What is given in the problem? What are you asked to find? two quantities expressed in scientific notation the quotient of the two quantities Items Data Measured quantity g ml Divide the coefficients, and subtract the exponents. Then transform the result to the correct form for scien- tific notation with the correct units and number of significant figures. 2. PLAN What steps are needed to divide the quantities expressed in scientific notation? 8 of 12

9 (P 10 Q ) (R 10 S ) Result written correctly in scientific notation, with the correct units and number of significant figures divide the coefficients and subtract the exponents in the order shown (P R) 10 (Q S) P 10 Q unit 1 R 10 S unit 2 quotient of coefficients P R 10 difference of exponents (Q S) if there is more or less than one nonzero digit to the left of the decimal, move the decimal and change the exponent to account for the move, then round to the correct number of significant figures quotient of units unit 1 unit 2 3. COMPUTE g ml (3 6) g ml g/ml The measurement ml has the fewest significant figures; round the result accordingly g/ml g/ml this digit is greater than 5, so round up To transform the result to the correct form for scientific notation, move the decimal point to the right one place and decrease the exponent by one g/ml ( 3 1) g/ml g/ml 4. EVALUATE Are the units correct? Is the quantity expressed to the correct number of significant figures? Is the quantity expressed correctly in scientific notation? Yes; grams divided by milliliters gives g/ml, a unit of density. Yes; the result was limited to two significant figures by the data given. Yes; there is only one nonzero digit to the left of the decimal point. 9 of 12

10 PRACTICE 1. Carry out the following computations, and express the result in scientific notation: a cm s ans: cm/s b L m 2 ans: L/m 2 c L km ans: 9.13 L/km d km min ans: km/min e g ( km km) ans: g/km 2 ADDITIONAL PROBLEMS 1. Express the following quantities in scientific notation: a km b L c cm 3 d mm 2 e g f m g J h g/l i kg j Hz 2. Perform the following calculations, and express the result in scientific notation with the correct number of significant figures: a kg kg kg b mg mg mg c m m m 3 d m m m e J J J f molecules molecules molecules g cm cm cm cm 10 of 12

11 3. Perform the following computations, and express the result in scientific notation with the correct number of significant figures: a L s b mm mm 2 c kg m 2 d km s e m m m f J s 4. Your electric company charges you for the electric energy you use, measured in kilowatt-hours (kwh). One kwh is equivalent to J. Express this quantity in scientific notation. 5. The pressure in the deepest part of the ocean is Pa. Express this pressure in scientific notation. 6. Convert 1.5 km to millimeters, and express the result in scientific notation. 7. Light travels at a speed of about km/s. a. Express this value in scientific notation. b. Convert this value to meters per hour. c. What distance in centimeters does light travel in 1 s? 8. There are molecules in cm 3 of a certain substance. a. What is the number of molecules in 1.09 cm 3 of the substance? b. What would be the number of molecules in cm 3 of the substance? c. What number of molecules are in cm 3 of the substance? 9. The number of transistors on a particular integrated circuit is , and the integrated circuit measures 9.5 mm 8.2 mm. a. What is the area occupied by each transistor? b. Using your answer from (a), how many transistors could be formed on a silicon sheet that measures 353 mm 265 mm? 10. A solution has g of a substance in 1.00 L. Express this concentration in grams per microliter. 11. Cesium atoms are the largest of the naturally occurring elements. They have a diameter of m. Calculate the number of cesium atoms that would have to be lined up to give a row of cesium atoms 2.54 cm (1 in.) long. 11 of 12

12 12. The neutron has a volume of approximately m 3 and a mass of g. Calculate the density of the neutron in g/m 3. What is the mass of 1.0 cm 3 of neutrons in kilograms? 13. The pits in a compact disc are some of the smallest things ever mass-produced mechanically by humans. These pits represent the 1s and 0s of digital information on a compact disc. These pits are only m deep (1/4 the wavelength of red laser light). How many of these pits would have to be stacked on top of each other to make a hole m deep? ml of oxygen gas contains oxygen molecules at 0 C and standard atmospheric pressure. a. How many oxygen molecules are in ml of gas? b. How many oxygen molecules are in 1.00 L of gas? c. What is the average space in milliters occupied by one oxygen molecule? 15. The mass of the atmosphere is calculated to be kg, and there are people living on Earth. Calculate the following values. a. The mass of atmosphere in kilograms per person. b. The mass of atmosphere in metric tons per person. c. If the number of people increases to , what is the mass in kilograms per person? 16. The mass of the sun is kg, and the mass of Earth is kilograms. How many Earths would be needed to equal the mass of the sun? 17. A new landfill has dimensions of 2.3 km 1.4 km 0.15 km. a. What is the volume in cubic kilometer? b. What is the volume in cubic meters? c. If objects averaging m 3 each are placed into the landfill each year, how many years will it take to fill the landfill? 18. A dietary calorie (C) is exactly equal to 1000 cal. If your daily intake of food gives you 2400 C, what is your intake in joules per day? (1 cal J) 12 of 12