PHYSICS

• a physical quantity is a quantity that can be measured. it consists of a numerical magnitude and a unit
• the 7 base quantities are length, mass, time, electric current, temperature, and amount of substance
• si unit of length is metre (m)
• si unit of mass is kilogram (kg)
• si unit of electric current is ampere (A)
• si unit of time is second (s)
• si unit of temperature is kelvin (K)
• si unit of amount of substance is mole (mol)
• size of a carbon atom is 0.1 x 10^-10m
• the factor of the prefix tera- is 10^12 and its symbol is T
• the factor of the prefix giga- is 10^9 and the symbol is G
• the factor of the prefix mega- is 10^6 and the symbol is M
• the factor of the prefix kilo is 10^3 and the symbol is k
• the factor of the prefix deci- is 10^-1 and its symbol is d
• the factor of the prefix centi- is 10^-2 and its symbol is c
• the factor of the prefix milli- is 10^-3 and the symbol is m
• the factor of the prefix nano- is 10^-9 and the symbol is n
• the factor of the prefix micro- is 10^-6
• to measure length we use metre rule, measuring tape, digital calipers and digital micrometer screw gauge
• a metre rule can measure length up to 1 metre
• measuring tape can measure lengths of several metres and measure straight or curved surfaces
• inside jaws of digital calipers are used to measure the internal diameter of an object
• the outside jaws of digital calipers are used to measure the external diameter or width of an object
• the locking screw of calipers are used to ensure the jaws do not move apart
• digital display of calipers are used to display the numerical value
• zero button of the digital calipers is used to reset the displayed length back to zero
• tail of digital calipers is used to measure the depth of an object
• digital micrometer screw gauge are used to measure objects that are too small to be measured using the digital calipers
• the smallest unit an instrument can measure is known as the precision
• measuring range of measuring tape is zero to several metres
• the smallest division of measuring tape is 0.1cm or 1mm
• example of use of measuring tape is a persons waist
• the measuring range of a metre rule is 0 to 1 metere
• the smallest division of metre rule is 0.1cm or 1mm
• example of usage of metre rule is the height of a table
• the measuring range of digital calipers is 0 to 15 cm
• the smallest division of digital calipers is 0.001 cm or 0.01mm
• example of usage of digital calipers is the diameter of a test tube
• the measuring range of digital micrometer screw gauge is 0 to 2.5 cm
• the smallest division of digital micrometer screw gauge is 0.0001 cm or 0.001 mm