What is physics?
It is a branch of science in which we study about the basic law of nature and their uses in different natural phenomena.
It comes from the Greek word meaning " nature".
Unit and Dimension
physical quantity -: Those quantity which can be measured by any means directly or indirectly is known as physical quantity.
Any physical quantity can be given by the formula -----
Q =nu
here Q = physical quantity
n = numerical value
u = its unit
Example - mass = 5 kg
Q = mass n = 5
u = kg
What is unit ?
unit of a physical quantity is a chosen standard of that quantity which differentiate it from other physical quantity.
what is numerical value ?
Numerical value of a physical quantity gives the comparison b/w different of the same physical quantity.
Types of physical quantity ---------:
1. fundamental quantities
2. derived quantities
Fundamental quantities Unit
mass kg
Time s
electric current A
Luminous intensity cd
Amount of substance mole
plane angle Radian
solid angle steradian
What is meter (m) ?
Luminous intensity cd
Amount of substance mole
plane angle Radian
solid angle steradian
The meter is the length of path travelled by light in vacuum during a time interval of 1/299,792,458 of a second
What is kilogram (kg) ?
The kilogram is equal to the mass of international prototype of kilogram (a platinum-iridium alloy cylinder) kept at international Bureau of weights and measures at serves near Paris , France (1889)
What is second (S) ?
The second is a duration of 9,192,631,770 periods of the radiation corresponding to transition b/w the two hyper fine levels of the ground state of the caesium -133 atom
What is Ampere (A) ?
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce b/w these conductors a force equal to 2*(10) to power -7 newton per meter of lengths.
What is Kelvin (k) ?
The kelvin is the fraction 1/273.16 degree of the thermodynamic temperature of triple point of water. What is mol ?
The mole is the amount of substance of a system which contains as many elementary entities as there are atom in 0.012 kg of carbon -12.
what is candela (cd) ?
The candela is the luminous intensity in a given direction of a source the emits of monochromatic radiation of frequency 540*(10)to the power 12 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
Derived quantity Units Force newton (N)
pressure Pascal
Resistance Ω ohm
Resistivity Ω m
Power watt
Energy Joule
current Ampere
Time Second
Distance Km
Wavelength (A)
frequency Hz Largest unit of mass - : c.s.l.(ChandraSekhar limit)
1 c.s.l. = 1.4 times the mass of sun . Largest unit of length -: par sec. 1 par sec. = 3.26 light year. Smallest unit of time -: shake 1 shake = 1/(10)to the power 8 sec .
✔ some important unit -:
1.Astronomical unit (Au) -: It is the mean distance b/w sun and earth.1 Au = 1.496*(10)to the power 11 m = 15 crore km .
2. light year -: It is the distance covered by light in 1 year. 1 (ly) =3*100000000*1*365*24*3600 m
= 9.46*(10)to the power 15 m
Par sec -: It is the distance at which the angle subtended by an arc. 💥 Dimension
Dimension of a physical quantity is the power by which fundamental quantities are raised to get the unit of that quantity.
👉 The formula which represent the dimension of physical quantities is called dimensional formula.
Fundamental Quantity -: [ Mass , Length , Time ]
Note -: All digit[0,1]are whole to the power to the M ,L ,T.
= [L ] * [ L ]
= [ L] *[L ]* [L ]
= [L3 ]
= [M ]/ [ L3] =[ M L-3 ] = [ M L-3 T0 ]
[Velocity] = [Displacement ]/[Time ]
=[ L ]/ [ T ] =[L T-1 ] = [M0 L1 T-1 ]
[ force ] = [ mass ]* [ acceleration ]
= [M1 L1 T-2]
[acceleration] = [change in velocity ]/[time]
[work] = force *displacement = [ M1L1T-2 ] * [ L]
=[M1 L2 T-2]
[displacement ] =[ M0L1T0]
[power ] = [work]/[time ]
= [L2 T-2 ]/[T] = [ M0 L2 T-3 ]
[pressure] = [force]/[Area]
[momentum] = [mass] * [velocity ]
=[M] *[L1T-1] = [M1L1T-1 ]
[Heat] = [work]
[frequency] = [1]/[time period] = 1/[T] = [M0L0 T-1 ]
[Amplitude] = [M0 L1 T0]
[wavelength] = [ velocity*time period ] =[L1T-1]*[T]
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