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2.7: Units Raised to a Power

  • Page ID
    364537
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    Learning Objectives

    • To convert unit raised to a power to a corresponding value in a different unit raised to the same power using conversion factors.

    Volume

    Volume is the measure of the amount of space occupied by an object. The standard SI unit of volume is defined by the base unit of length (Figure \(\PageIndex{1}\)). The standard volume is a cubic meter (m3), a cube with an edge length of exactly one meter. To dispense a cubic meter of water, we could build a cubic box with edge lengths of exactly one meter. This box would hold a cubic meter of water or any other substance.

    CNX_Chem_01_04_Volume.jpg
    Figure \(\PageIndex{1}\): (a) The relative volumes are shown for cubes of 1 m3, 1 dm3 (1 L), and 1 cm3 (1 mL) (not to scale). (b) The diameter of a dime is compared relative to the edge length of a 1-cm3 (1-mL) cube.

    A more commonly used unit of volume is derived from the decimeter (0.1 m, or 10 cm). A cube with edge lengths of exactly one decimeter contains a volume of one cubic decimeter (dm3). A liter (L) is the more common name for the cubic decimeter. One liter is about 1.06 quarts. A cubic centimeter (cm3) is the volume of a cube with an edge length of exactly one centimeter. The abbreviation cc (for cubic centimeter) is often used by health professionals. A cubic centimeter is also called a milliliter (mL) and is 1/1000 of a liter.

    Conversions

    Conversion factors for area and volume can also be produced by the dimensional analysis method. Just remember that if a quantity is raised to a power of 10, both the number and the unit must be raised to the same power of 10. For example, to convert \(1500 \: \text{cm}^2\) to \(\text{m}^2\), we need to start with the relationship between centimeter and meter. We know that 1 cm = 10-2 m or 100 cm =1 m, but since we are given the quantity in 1500 cm2, then we have to use the relationship:

    \[1\, cm^2 = (10^{-2}\, m)^2 = 10^{-4}\, m^2\]

    CONCEPT MAP

    To convert centimeters squared to meters squared, use the conversion factor 0.01 meters per 1 centimeter,  squared overall

    CALCULATION

    \[1500 \: \cancel{\text{cm}}^2 \times \left( \frac{10^{-2} \: \text{m}}{1 \: \cancel{\text{cm}}} \right)^2 = 0.15 \: \text{m}^2\]

    or

    \[1500 \: \cancel{\text{cm}}^2 \times \left( \frac{1 \: \text{m}}{100 \: \cancel{\text{cm}}} \right)^2 = 0.15 \: \text{m}^2\]

    or

    \[1500 \: \cancel{\text{cm}}^2 \times \frac{1 \: \text{m}^2}{10,000 \: \cancel{\text{cm}^2}} = 0.15 \: \text{m}^2\]

    Example \(\PageIndex{1}\): Volume of a Sphere

    What is the volume of a sphere (radius 4.30 inches) in cubic cm (cm3)?

    Solution

    Steps for Problem Solving

    What is the volume of a sphere (radius 4.30 inches) in cubic cm (cm3)?
    Identify the "given” information and what the problem is asking you to "find."

    Given: radius = 4.30 in

    Find: cm3 (volume)

    Determine other known quantities.

    Volume of a sphere: V = \(\frac{4}{3} \times \pi \times r^3 \)

    = \(\frac{4}{3} \times 3.1416 \times (4.3\underline{0}in)^3 \)

    = \(33\underline{3}.04 in^3\)

    Prepare a concept map.

    To convert inches cubed to centimeters cubed,  use conversion factor 2.54 centimeters per 1 inch, cubed overall

    Calculate.

    \(33\underline{3}.04 \cancel{in^3} \left(\frac{2.54cm}{1 \cancel{in}}\right)^3 = 5.46 \times10^3 cm^3\)

    Think about your result.

    A centimeter is a smaller unit than an inch, so the answer in cubic centimeters is larger than the given value in cubic inches.

    Exercise \(\PageIndex{1}\)

    Lake Tahoe has a surface area of 191 square miles. What is the area in square km (km2)?

    Answer
    495 km2

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