Definitions of base units

Definitions of base units


Metre


The distance travelled by light in vacuum during a time interval of  1/299,792,458 second is called 1 metre.


Kilogram


The Kilogram is the mass of cylinder made of planitum-iridium alloy kept at International Bureau of Weights at Sevres near Paris in France.


Second

The time duration in 9,192,631,770 time periods of the selected transition of radiation of Cesium-133 atom is defined as 1 s.

Ampere
It is the steady current (a unit of measure of the rate of electron flow ) that when flowing in straight parallel wires of infinite length and negligible cross section, separated by a distance of one meter in free space, produces a force between the wires of 2 × 10-7 newtons per meter of length.

The ampere is named after Andre Marie Ampere, French physicist (1775-1836).



Kelvin

A temperature scale in which The fraction 1/273.16) of the thermodynamic temperature of triple point of water is called the Kelvin.



Mole


The amount of a substance that contain as many elementary entities (molecules, atoms and  ions if the substance is monatomic) as there are number of atoms in 0.012 kg of carbon-12 is called a mole.The number is 6.0225 × 1023, or Avogadro's number. Also called gram molecule.




Candela

It is the Standard International (SI) unit to measure the brightness of a source of light (  luminous intensity. one square centimeter of a blackbody  at the freezing point of platinum emits one-sixtieth of a candela of radiation. 

Introduction to physics

Physical science analyze the branches of natural science and the study of non living things. Examples of physical sciences are physics, chemistry, geography,meteorology,hydrology, geology, astronomy, astrology and oceanography.

Definition of Physics- Physics is a natural science which involves the study of matter and their manifestation in different natural phenomena.

Physics come from the greek word 'physis' meaning "nature'. Physics is a fundamental science because the other natural sciences like biology, chemistry, geology,astronmomy, geoscience etc deal with systems that use and obey the laws of physics.

cbse class 11th ist lesson Physical world

Force

iit entrance- Wavemotion

longitudinal wave


This animation depicts Transverse and Longitudinal waves on a spring.



For transverse waves the disturbance (in this case the displacement of the slinky) is PERPENDICULAR to the direction the wave is moving (in this case along the slinky). For Longitudinal waves the disturbance is ALONG the direction the wave is moving. In some materials these two waves go at different speeds, and in fluids (liquids or gases) transverse sound waves don't go at all! (This is important for earthquake vibrations going through the earth's core).

A transverse wave is created by a disturbance that is perpendicular to the direction the wave will travel.


A longitudinal wave is created by a disturbance that is along the direction the wave will travel.




Physics: Transverse vs. longitudinal waves. Wave graphs. Velocity (v) versus frequency (f); frequency (f) versus angular frequency (ω)