Optics (Physics) Part-I

Photon energy is directly proportional to the wave frequency and inversely proportional to the wavelength.

where, E = energy of photon

h = Planck's constant

c = speed of light in a vacuum

λ = wavelength

Thus, among the given options 200-280 nm radiation has the highest energy per quantum. Ultraviolet radiation contains sufficient energy per quantum to damage living cells.

The ultraviolet spectrum is divided into UV-A (320-400 nm) responsible for tanning the skin; UV-B (280-320 nm) responsible for skin cancer and vitamin D synthesis; and UV-C (below 280 nm), potentially the most harmful waveband but absorbed almost completely by molecular oxygen in the stratosphere.

The electromagnetic spectrum encompasses all type of radiations. The part of the spectrum that reaches earth from the sun is between 100 nm to 10⁶ nm. This band is broken into three ranges - Infrared (above 700 nm), Visible (400 to 700 nm), Ultraviolet (below 400 nm).

Visible light is that part of electromagnetic radiation which can be seen by human eyes. Visible light is usually defined as having wavelengths in the range of 400-700 mm (4000-7000Å), between the infrared and ultraviolet.

A typical human eye will respond to wavelengths from about 380 to 750 nm. Thus, among the given options, option (d) will be the right answer.

Visible light is that part of electromagnetic radiation which can be seen by human eyes. Visible light is usually defined as having wavelengths in the range of 400-700 mm (4000-7000A), between the infrared and ultraviolet.

A typical human eye will respond to wavelengths from about 380 to 750 nm. Thus, among the given options, option (d) will be the right answer.

Eye is most sensitive to yellowish-green light that is light of wavelength about 5550 Å or 555 nm.

In normal lighting conditions, photo receptor cells in human eye are most sensitive to colours between the wavelengths of 530-570 nanometre. The sensitivity of our eyes is most for yellowish-green colour.

The human ear is most sensitive to sounds between 1000 and 5000 Hz. The human eye is most sensitive to yellowish-green colour. When fully light-adapted, the human eye features a wavelength response from around 400 to 700 nanometers, with a peak sensitivity at 555 nanometers (in the yellowish-green region of the visible light spectrum).

The impression of sound heard by our ears persist in our mind for 1/10ᵗʰ of a second. If another sound is heard before 1/10 second is over, the impression of the two sound mixes up and our mind cannot differentiate among the two.

Persistence of vision is a phenomenon of the human eye wherein the image formed on the retina is retained by the brain for 1/16ᵗʰ of a second. Hence, statement of option (b) is incorrect.

The light has a dual nature, sometimes it behaves as wave and sometimes as particle. In the later part of the 19th century and in the beginning of 20th century, it was realized that black body radiation and the photoelectric effect can be understood only on the basis of particle model of light.

Some experiments require light to be a wave, while others require light to be a particle. This led to the acceptance of dual nature of light. Quantum mechanics explains the duality of light by describing it as a wave-packet. A wave-packet refers to waves that may interact either as spatially localized, acting as particle, or interacting like waves.

Due to its very small wavelength, the light appears to travel in a straight line.

The speed of light in a vacuum is 3.00 × 10⁸ m/s, while the speed of sound in vacuum is zero and in air is 343 m/sec. The speed of light in glass is 2.0 × 10⁸ m/s. The velocity of light always greater than the velocity of sound. The velocity of celestial objects and the rockets is quite low than the velocity of light.