H2 Physics Summary for all topics

A1 SI base units In the SI system of units, there are seven base quantities and their units. These 7 quantities are assumed to be mutually independent. Base Quantities SI Base Units Name Symbol Length metre m Mass kilogram kg Time seconds s Current ampere A Temperature kelvin K Amount of substance mole mol Luminous Intensity candela cd Derived Quantities Derived quantities are physical quantities expressed in terms of one or more bas e quantities. General rules for determining the units of derived quantities: 1) For addition / subtraction of two or more quantities, each quantity must have the SAME unit. 2) For multiplication / division, rules of algebraic multiplication and division apply. 3) Exponents (powers/indexes) are unitless. Homegeneity of Physical Equations • Each term in an homogeneous equation has the same units. • For any two quantities to be equated, added or subtracted , they must have the same dimension (or units). • Homogeneous equation may not be correct (e.g. missing terms / coefficients) but a non - homogeneous equation must be wrong. Prefixes (Order of magnitudes) Can be added to SI base units and derived units to make larger or smaller units. (e.g. 1 ms = 10−3 s, 1 km = 103 m ) Name Symbol Factor pico p × 10−12 nano n × 10−9 micro μ × 10−6 milli m × 10−3 centi c × 10−2 deci d × 10−1 kilo k × 103 mega M × 106 giga G × 109 tera T × 1012 Systematic Error & Random Error Systematic errors have the same magnitude and sign when measurements are repeated. Causes: Instrument errors (e.g. zero errors), Environmental conditions, Poor experimental techniques (e.g. parallax error). Systematic error can be eliminated if the source of the error is known. Random errors have different magnitudes and signs (i.e. varying both magnitude and direction) when measurements are repeated. Causes: Variations in environmental conditions, Irregularity of the quantity being measured, Limitation of equipment. Random error cannot be completely eliminated but can be minimised by finding the average of repeated measurements. Precision & Accuracy Precision refers to how close the repeated measured values are to each other , without regard to the true value of the quantity. Repeated measurements which are very close to one another are precise measurements. Thus an experiment which has small random errors (i.e. small spread of readings) is said to have high precision. Accuracy refers to how close a measured value is to the true value of a quantity. An experiment which has small systematic errors is said to have high accuracy. The average value is close to the true value. Errors / Uncertainties When making any measurement, there is always some uncertainty / error. Experimental uncertainty or error = Measured value – True value Absolute error / uncertainty – e.g. error / uncertainty in measuring length, Fractional error / uncertainty – e.g. Percentage error / uncertainty – e.g. G