E-Lecture - Important Points
- The comparison of any physical quantity with its standard unit is called measurement.
- Systems of measurement: the metric system, the British imperial and the United States Customary systems
- Physical Quantities which cannot be expressed in terms of any other quantity are called fundamental.
- Physical quantities which depend on one or more fundamental quantities for their measurements are known as derived quantities.
- Words or symbols that represent the factors of ten are called prefixes.
- A conversion factor is a fraction that is equal to one used to convert a unit from one system to another.
- The number of figures required to specify a certain measurement are called significant figure.
- Accuracy is how close a measurement is to the true or accepted value.
- Precision is the degree of consistency and agreement among independent measurements of the same quantity.
- Uncertainty is a quantitative measure of how much your measured values deviate from a standard or expected value.
- Measurement error is the difference between a measured value and the true value for that measurement.
- Systematic errors are errors that are consistently in the same direction, they are one-sided errors.
- Random errors are errors that cause your measurements to be sometimes above the accepted value and sometimes below the accepted value.
- Pressure is defined as the amount of force exerted (thrust) on a surface per unit area.
- The density (ρ) of matter can be defined mathematically as the mass divided by the volume.
- The relative density (RD) or specific gravity (SG) of a substance is the ratio of density of a substance to the density of water at 4oC.
- The pressure of a static (non-flowing) liquid is: Pressuregh = ρgh
- The total pressure, or absolute pressure, is thus the sum of gauge pressure and atmospheric pressure: Ptotal = Patm + ρhg
- Pascal’s Principle: ”A change in pressure applied to an enclosed fluid is transmitted unchanged to every point within the fluid”
- The pressure due to the sea of air which surrounds us is called atmospheric pressure. Atmospheric pressure decreases with increasing height.
- Atmospheric pressure is measured using an instrument called a barometer.
- A manometer measures the pressure acting on a column of fluid. It is made from a U-shaped tube open on both ends.
- The relationship between temperature and pressure of a gas:
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- The relationship between volume and pressure of a gas: P1V1 = P2V2
- The dimension of a physical quantity refers to the fundamental units contained in it.
- The expression for a physical quantity in terms of the fundamental physical quantities is called the dimensional expression or equation.
- Meter rule, Vernier calipers, and micrometers are instruments for measuring distances or length.
- Beam balance, spring balance, table balance, platform balance, postal balance, triple balance are used for the measurement of mass.
- A stopwatch an instrument used to measure time intervals.
- Electronic balance is an instrument used in the accurate measurement of mass of an object.
- Thermometer is the device used to measure the temperature of an object or place.
- Physical quantities that have only a magnitude and no direction are called scalars.
- Physical quantities which need both magnitude and direction for their description are called vectors.
- A method of writing very big and very small numbers using the powers of ten is known as scientific notation.
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