40
Units of Scientific Measurements
24. A soap bubble is 3.0 inches in diameter and made of a film that is 0.010 mm
thick. How thick will the film be if the bubble is expanded to 15 inches in
diameter?
25. (a) A cube measures 1.00 cm on an edge. What is the surface area? (b) The
cube is crushed into smaller cubes measuring 1 .00 mm on an edge. What is the
surface area after crushing? (c) Further crushing gives cubes measuring 100 A
on an edge. What is the surface area now? How many football fields (160
ft x 100 yd) would this make?
26. The unit of viscosity (77) is called a poise. Viscosity is determined experimentally by measuring the length of time (t) for a certain volume (V) of liquid to
run through a capillary tube of radius R and length L under a pressure P ,
according to the Poiseuille equation
P-rrtR
4
What are the units of a poise in the centimeter-gram-second (cgs) system?
27. The energy of a quantum of light is proportional to the frequency (i/) of the
light. What must be the units of the proportionality constant (h) ifE = hvl E
is expressed in ergs, and v has the units of sec"
1
.
28. Show that the product of the volume of a gas and its pressure has the units of
energy.
PROBLEMS B
29. What are the area and the volume of a bar measuring 2 x 4 x 20 cm?
30. What are the area and the volume of a cylindrical rod with hemispherical ends
if the rod is 1.00 inch in diameter and has an overall length of 55.54 cm?
31. The driving distance between Los Angeles and San Francisco by one route is
420 miles. Express this in kilometers.
32. A common type of ultraviolet lamp uses excited mercury vapor, which emits
radiation at 2537A. Express this wavelength (a) in centimeters, and (b) in
nanometers.
33. A certain spectral line of cadmium often is used as a standard in wavelength
measurements. The wavelength is 0.000064384696 cm. Express this wavelength (a) in angstroms, and (b) in nanometers.
34. What must be the velocity in miles per hour of a jet plane if it goes at twice the
speed of sound? (The speed of sound is 1000 ft/sec under the prevailing conditions.)
35. The domestic airmail rate is B cents per ounce or fraction thereof. How much
postage will be required for a letter weighing 76 g? Give your answer in terms
ofB.
Units of Scientific Measurements
24. A soap bubble is 3.0 inches in diameter and made of a film that is 0.010 mm
thick. How thick will the film be if the bubble is expanded to 15 inches in
diameter?
25. (a) A cube measures 1.00 cm on an edge. What is the surface area? (b) The
cube is crushed into smaller cubes measuring 1 .00 mm on an edge. What is the
surface area after crushing? (c) Further crushing gives cubes measuring 100 A
on an edge. What is the surface area now? How many football fields (160
ft x 100 yd) would this make?
26. The unit of viscosity (77) is called a poise. Viscosity is determined experimentally by measuring the length of time (t) for a certain volume (V) of liquid to
run through a capillary tube of radius R and length L under a pressure P ,
according to the Poiseuille equation
P-rrtR
4
What are the units of a poise in the centimeter-gram-second (cgs) system?
27. The energy of a quantum of light is proportional to the frequency (i/) of the
light. What must be the units of the proportionality constant (h) ifE = hvl E
is expressed in ergs, and v has the units of sec"
1
.
28. Show that the product of the volume of a gas and its pressure has the units of
energy.
PROBLEMS B
29. What are the area and the volume of a bar measuring 2 x 4 x 20 cm?
30. What are the area and the volume of a cylindrical rod with hemispherical ends
if the rod is 1.00 inch in diameter and has an overall length of 55.54 cm?
31. The driving distance between Los Angeles and San Francisco by one route is
420 miles. Express this in kilometers.
32. A common type of ultraviolet lamp uses excited mercury vapor, which emits
radiation at 2537A. Express this wavelength (a) in centimeters, and (b) in
nanometers.
33. A certain spectral line of cadmium often is used as a standard in wavelength
measurements. The wavelength is 0.000064384696 cm. Express this wavelength (a) in angstroms, and (b) in nanometers.
34. What must be the velocity in miles per hour of a jet plane if it goes at twice the
speed of sound? (The speed of sound is 1000 ft/sec under the prevailing conditions.)
35. The domestic airmail rate is B cents per ounce or fraction thereof. How much
postage will be required for a letter weighing 76 g? Give your answer in terms
ofB.