physics notes o level

Chapter 1: Physical Quantities, Units, Measurement

What are physical quantities? -A physical quantity is a quantity that can be measured -It consists of a numerical value and a unit -There are 7 basic physical quantities, of which others are derived from Base quantity SI unit Symbol for SI unit length metre m mass kilogram kg time second s electric current ampere A thermodynamic temperature kelvin K amount of substance mole mol luminous intensity candela cd (luminous intensity is not tested at our level) Prefixes for SI units -Using decimal notation, 1 km can be expressed as 1000 m -This is not efficient, so prefixes are more commonly used Order of magnitude Prefix Symbol Amount 10^12 tera- T 1000000000000 (trillion) 10^9 giga- G 1000000000 (billion) 10^6 mega- M 1000000 (million) 10^3 kilo- k 1000 (thousand) 10^-1 deci- d 0.1 10^-2 centi- c 0.01 10^-3 milli- m 0.001 10^-6 micro- µ 0.000001 10^-9 nano- n 0.000000001

Standard form -Other than using prefixes, standard form is also a method of writing physical quantities in which 1 or 10 is multiplied by an appropriate power of 10 -e.g. 1 km = 1 x 10^3 m -The order of magnitude of some measure is the 10^x part -e.g. Order of magnitude of radius of earth 10^6 m Order of magnitude of diameter of earth 10^7 m Order of magnitude of size of atom 10^-10 m Measurement of length Metre ruler and measuring tape -The metre ruler and measuring tape are commonly used to measure length -A metre ruler can measure distances of up to 1 metre -The measuring tape can measure straight distances longer than 1 metre -A cloth measuring tape can measure the length along a curved surface Digital calipers -Digital calipers can measure the internal and external diameter of an object and the depth of an object accurately Digital micrometer screw gauge -The digital micrometer screw gauge is used to measure objects which are too small to be measured using the digtial calipers

Measurement of time Pendulum -A pendulum consists of a heavy object called a bob tied to a string -When a pendulum is swung, it will move back and forth at regular intervals -Each complete back and forth motion of the pendulum is called an oscillation Pendulum clock -A pendulum clock is clock which keeps time using a pendulum Clocks and stopwatches -The oscillations of springs and the natural vibrations of crystals are other motions used to keep track of time -Most clocks and stopwatches today use quartz crystals as they are small, accurate and require little electric power Precision of an instrument -The smallest unit an instrument can measure is known as its precision Instrument Measuring range Precision measuring tape 0 to several metres 0.1 cm or 1 mm metre ruler 0 to 1 metres 0.1 cm or 1 mm digital calipers 0 to 15 centimetres 0.001 cm or 0.01 mm digital micrometer screw gauge 0 to 2.5 centimetres 0.0001 cm or 0.001 mm

Avoiding errors of measurment Parallax erro