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Here is the extracted text in markdown format: ## Atom | Gamma Ray | UV Ray | Infra-red | Radiowave | | :-------- | :------- | :-------- | :-------- | | $10­^{-12} m$ | $10^{-8} m$ | $10^{-5} m$ | $10^{3} m$ | | X Ray | Visible Light | Microwave | | | $10^{-10} m$ | $10^{-6} m$...

Here is the extracted text in markdown format: ## Atom | Gamma Ray | UV Ray | Infra-red | Radiowave | | :-------- | :------- | :-------- | :-------- | | $10­^{-12} m$ | $10^{-8} m$ | $10^{-5} m$ | $10^{3} m$ | | X Ray | Visible Light | Microwave | | | $10^{-10} m$ | $10^{-6} m$ | $10^{-4} m$ | | ## Diameter of earth | Quantity | Symbol | Unit | Quantity | Symbol | | :------------------------------ | :----- | :----------------- | :------------------------------ | :------- | | Length | l, L | km,cm,mm | potential difference*/voltage | V | | area | A | $m2, cm2$ | current* | I | | volume | V | $m3,cm3$ | charge | q, Q | | weight* | W | N | e.m.f.* | E | | mass | m, M | kg, g, mg | resistance | R | | time | t | h, min, s, ms | half-life | t 1/2 | | period* | T | s | proton number | Z | | density* | p | g/cm3, kg/m3 | nucleon number | A | | speed | u, v | km/h, m/s, cm/s | activity of a radioactive source | A | | acceleration* | a | m/s2 | | | | acceleration of free fall | g | m/s2 | | | | force* | F, f | N | | | | moment of force* | M | Nm | | | | work done* | W, E | J | | | | energy | E | J, kWh | | | | power* | P | W | | | | pressure* | P | Pa*, N/m, mm Hg | | | | temperature | T | °C, K | | | | frequency* | f | Hz | | | | wavelength* | $\lambda$ | m, cm | | | | focal length | f | m, cm | | | | angle of incidence | i | degree (°) | | | | angles of reflection, refraction | r | degree (°) | | | ## Scalar and Vector Quantities - Scalar quantities are physical quantities that have magnitude only. - Vector quantities are physical quantities that have both magnitude and direction. | Scalar | Vector | | :----------- | :----------- | | Distance | Displacement | | Speed | Velocity | | Energy | Force | | Time | Acceleration | | Volume | | | Density | | | Power | | | Mass | | ## 1.3 How Do We Measure Physical Quantities? ### Measurement of Length - The SI unit for length is metre (m). - The instruments that can be used to measure length are metere ruler, measuring tape, digital calipers and digital micrometer screw gauge. ### Metre Rule and Measuring tape - A metre rule can measure lengths of up to one metre. - A measuring tape can measure lengths of up to several meters and measure straight distances or curved surfaces