Practical units measurement methodMarch 13, 2018
Error in Measurement Absolute RelativeMarch 14, 2018
Physical quantities units Measurement
Today our topic units measurement so far we have studies about Length, Mass and Time today we will study rest of the units and its measurement lets start the topic.
|Physical quantities units Measurement|
Electric Current ?
With the help of Length, Mass and time we can’t measure electric current so an another basic quantity required for measurement of current and its unit named as ampere we see electric current uses everywhere like bulb, fan, AC, washing machine, refrigerator and many more now the important question is how much electric current required for each equipment to run some equipment required more current and some required less amount of electric current we made its unit ampere for measurement suppose fan takes one ampere and AC takes 10 ampere computer takes 2 ampere then we see different amount of energy each equipment takes and this is calculated by ampere latter in current chapter we will see current definition but at the moment we will see what is one ampere current, how much powerful is one ampere current, then question arises how we measure current, the answer is current measured by its effect when current flows many types its effect shows like heating effect wire will become heated, magnetic field effect when current passes through wire it creates a magnetic field around the wire when we do electrolysis metal collected from solution like silver nitrate silver will be collected from solution during electrolysis if more current will be there more silver will be collected then we can say current value is more so we can made current definition with the help of current effect hence in SI system which effect of current was considered and how definition made for one ampere the answer is magnetic effect now deep analysis of magnetic effect. we took two rod of length one meter each and place parallel to each other at a distance of one meter apart now on left side rod we made such arrangement so that it can slide left side rail track now on left side rod we hang a weight of 2*10^-7 newton force with the help of a pulley now current is supply in the both rod by a battery and adjusted value with a variable resistance. now see as the weight of 2*10^-7 newton force applied on left side rod it will slide towards left but due to current supply in both rod magnetic field will be created and both rod will attract each other but right rod is fixed left is only movable what will happen on left rod two forces on left rod will act one due to weight in direction of left and other due to magnetic field in direction of right side at the moment when both forces become equal adjusting through variable resistance this time value of current is measured by ammeter and this is called one ampere.hence one ampere current is that value which balances 2*10^-7 newton force. similarly ammeter is connected through fan and if this ammeter stop at 2 ampere then we say fan is taking 2 ampere current same for AC if this ammeter stop at 10 ampere we say AC taking 10 ampere current.
Water has a condition when we cold it then become ice or when we heat is then become steam this condition may be changes if we decrease air pressure or increase air pressure then water become ice at different temperature or steam at different temperature here we see temperature changes for ice or steam changing the pressure now suppose in a glass of water we put some ice in water glass now there is two state of water one is solid that is ice and other is liquid water now we start to decrease the air pressure and this pressure becomes very low then we see from glass vapor is coming out now this is gas state now at this pressure and temperature water state is called triple state that is liquid, solid and gas at this pressure and temperature water is called triple point of state at that time of temperature is called one kelvin hence at triple point temperature of water is zero degree Celsius which is equal to 273.16 kelvin hence one kelvin is equal to (triple point)/273.6
Amount of Substance ?
What is mole answer is mole is a number like one dozen of banana means 12 banana similarly one mole atoms, one mole electrons now question is one mole what is that number actually we are familiar with number like, 100, 1000, 2000, 10000 etc but not frequently use mole and recognize this number but in SI system mole is accepted as standard counting then how much is this number for this take carbon of 0.012 kg that is 12 gram and spread it powder and now start counting how much of atoms you will found in powder that number will be called one mole if same number of electron taken then we can say one mole of electron if we take same number of molecules then it called one mole molecules so one mole is simply a number and its sample is carbon and it is equal to 6.022*10^23 this is also known as Avogadro’s number.
Luminous intensity is a brightness of anything like bulb, tube light, moon, sun every brightness is different from other like 100 watt and 200 watt bulb brightness will be different we can’t measure brightness with the help of length, mass, time, temperature, current so we have to made an another basic quantity luminous intensity then how it is defined for this measurement we count how much of energy packet that object send to our eyes per second that is energy per second this is power if object send more power than we say that object brightness is high like when we see sun our eyes get disturb immediately means sun power is high we can see light candle because it send low power hence we have to define one candela how much of light and which light wait light color is not yellow it is our imagination then which light taken for candela we know light color depend upon frequency so we taken radiation of frequency 540*10^12 Hertz so when you see this frequency chart you will found that is yellow light frequency which comes from candle in yellow there are so many frequency but we have fixed this frequency for light.hence how much of energy will be equal to one candela the answer is emit energy 1/683 watt is called one candela so in that way we measure light brightness but it must come in one steradian solid angle now so far we have discussed all seven basic units and two supplementary unit Plan angle is equal to arc divided by its radius and its unit is radian and solid angle is area divided by radius square so all unit is finished now wait litter is also a unit but we have not seen so this is called practical unit we will see in next post i hope your units concepts has been cleared thanks for reading
Physical quantities units Measurement