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Powerpoint Templates

Measurement

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There are seven basic unit in SI. The base unit for the length is meter. The other base units are: kilogram for mass, second for time, ampere for electric current, Kelvin for temperature, candela for luminous intensity and mole for amount of substance.

Metric System of Measurement

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Conversion Factors

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Significant Figures

Significant figures in measurement expression comprise all digits that are known with certainty, plus the first digit that uncertain. The position of the decimal point is irrelevant

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Zero in Measurement Expression

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Scientific NotationScientific work often

involves the use of numbers that are extremely or exceedingly small. The speed of light is approximately 30 0000 000 000 cm/s. The mass of the earth is approximately 6 000 000 000 000 000 000 000 000 000 g and many others like the electron mass, and wavelength of light are exceeding small. Those numbers are inconvenient to write, difficult to read and cumbersome to use in calculation.

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Solving Problem involving conversions

Suppose an object travels 555 m in 15.0 s. It average speed is

Formula :

Based on the definition of speed its dimension are length/time. The dimensions of speed are also specified in the derived units m/s.

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Mass is defined as the amount of matter a body contains.

Formula :

Volume is the space occupied by matter.

Density the amount of matter a body contains per unit volume.

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Example : A cubical metal box which is 250cm long is half- filled with soil. How many

grams of soil needed to half- fill box if the density of the soil is 1.2g/cc. Your final answer be expressed in scientific notation.

Given:

Required:

Solution:

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Mole• A mole is the amount of pure substance containing the same number of

chemical units as there are atoms in exactly 12 grams of carbon-12 (6.023 X 1023). This involves the acceptance of two dictates ,the scale of atomic masses and the magnitude of the gram. Both have been established by international agreement.

• Formerly, the connotation of mole was gram molecular weight current usage tends to apply the term mole to an amount containing Avogadro’s number of whatever units are being considered.

Formula:

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If a piece of sodium metal contains 6.525 x 10 atoms, how many grams will weigh?

23

Example:

Given: Find:

Solution: