Units and measurements Flashcards
Physical Quantity
A quantity which can be measured and by which various physical happenings can be explained and expressed in form of laws.
Physical quantity (Q)=
Magnitude Unit = nu where n is the numerical value and u is the unit
nu= constant that implies
n1u1 = n2u2 = constant therefore n ∝ 1/u
Fundamental or base or absolute Quantities
Out of the large number of physical quantities which exist, there are only few quantities which are independent of all other quantities and do not require the help of any other physical quantity for its definition ∴ these are called absolute quantities.
Base quantity- Length
Name- metre
symbol- m
Base quantity- Mass
Name- Kilogram
symbol-kg
base quantity- Time
Name- second
symbol- s
base quantity- electric current
Name- ampere
symbol- A
base quantity- Thermodynamic temperature
Name- Kelvin
symbol- K
Base quantity - amount of substance
Name- Mole
symbol- mol
base quantity- Luminous intensity
Name- Candela
symbol- cd
Supplementary physical quantities
dimensionless units have been combined alongside base units just to generate derived units are known as supplementary quantities. Supplementary quantities are of two types, such as: Plane angle - radian (rad) Solid angle - steradian (sr)
Plane angle θ
it is a dimensionless quantity
the plane angle as the ratio of arc length to the radius. That is, if θ is the plane angle, s is the arc length and r is the radius, then, θ=s/r (theta =s/r is called the parallax method )
SI unit of plane angle θ
Radian [rad]
what is Radian ?
Rather than dividing a circle into some number of segments (like 360 degrees), mathematicians often prefer to measure angles using the circumference
You can think of radians as the “distance traveled” along the circumference of a unit circle. This is particularly useful when working with objects that are moving on a circular path.
