भौतिकी संग्रहित करें

Television, computers, domestic appliances, and nuclear weapons.

The word 'physics' comes from the Latin physica ('study of nature'), which itself is a borrowing of the Greek φυσική (phusikḗ 'natural science').

The term derived from φύσις (phúsis) is 'origin, nature, property'.

The Sumerians and ancient Egyptians had knowledge of astronomy dating before 3000 BCE.

Advances in thermodynamics led to the development of industrialization.

Total internal reflection (TIR) is the phenomenon where waves arriving at the interface from one medium to another are not refracted into the second medium, but completely reflected back into the first medium. It occurs when the second medium has a higher wave speed than the first, and the waves are incident at a sufficiently oblique angle on the interface. TIR occurs not only with electromagnetic waves such as light and microwaves, but also with other types of waves, including sound and water waves. If the waves are capable of forming a narrow beam, the reflection tends to be described in terms of 'rays' rather than waves; in a medium whose properties are independent of direction, the 'rays' are perpendicular to the associated wavefronts.

An example of TIR is the water-to-air surface in a fish tank, where when viewed obliquely from below, it reflects the underwater scene like a mirror with no loss of brightness. This occurs due to the higher wave speed (lower refractive index) of air compared to water, and the oblique angle of incidence on the interface.

Refraction is generally accompanied by partial reflection when waves are refracted from a medium of lower propagation speed to a medium of higher propagation speed, such as from water to air. The angle of refraction is greater than the angle of incidence, which results in partial reflection. An illustration of this concept can be observed when light waves pass from water into the air, where some of the light is refracted and some is reflected, resulting in the formation of a rainbow.

Rays are used to describe the reflection of waves when the waves are capable of forming a narrow beam. This is because in such scenarios, the reflection tends to be described in terms of 'rays' rather than waves. In a medium whose properties are independent of direction, such as air, water, or glass, the 'rays' are perpendicular to the associated wavefronts.

Total internal reflection occurs when the second medium has a higher wave speed (i.e., lower refractive index) than the first, and the waves are incident at a sufficiently oblique angle on the interface. This phenomenon is related to the refractive index and wave speed, as the difference in wave speed and refractive index between the two media determines whether TIR will occur at the interface.