The materials (phosphors) that coat the inside of a fluorescent lamp convert ultravioletradiation (from the mercury- vapor discharge inside the tube) into visible light. Could one alsomake aphosphor that converts visible light to ultraviolet ? Explain.

A 124 W bulb converts only 15 % of the energy supplied to it into visible light of wavelength 640 nm . How many photons are emitted by the light bulb in one second ?

Which of the following is correct? (i) A fluorescent lamp, like the ones commonly found in offices, is a discharged tube in which the inner surface is coated with a fluoresecnet material such as zinc sulphide which is also used on TV screen. (ii)The fluorescent tube is filled with ercury vapor at low pressure. Excitation of the Hg atoms by electron bombardment cause the emission of light in the green, blue, and ultraviolet (UV) regions. (iii) When the light strike the inner glass wall, most of the UV light is abosorbed by the fluorescent material, which then emits a multitude of longer wavelengths that combine to produce white light. (iv) Fluorescent lamps are more enegry-efficient and, hence, cheaper to operate than tungsten lamp (ordinary light bulbs).

Read the following text and answer the following questions on the basis of the same: Laser: Electromagnetic radiation is a natural phenomenon found in almost all areas of daily life, from radio waves to sunlight to X-rays. Laser radiation - like all light - is also a form of electromagnetic radiation Electromagnetic radiation that has a wavelength between 380 nm and 780 nm is visible to the human eye and is commonly referred to as light. At wavelengths longer than 780 nm, optical radiation is termed infrared (IR) and is invisible to the eye. At wavelengths shorter than 380 nm, optical radiation is termed ultraviolet (UV) and is also invisible to the eye. The term "laser light" refers to a much broader range of the electromagnetic spectrum that just the visible spectrum, anything between 150 nm up to 11000 nm (i.e. from the UV up to the far IR). The term laser is an acronym which stands for "light amplification by stimulated emission of radiation". Einstein explained the stimulated emission. In an atom, electron may move to higher energy level by absorbing a photon. When the electron comes back to the lower energy level it releases the same photon. This is called spontaneous emission. This may also so happen that the excited electron absorbs another photon , releases two photons and returns to the lower energy state. This is known as stimulated emission. Laser emission is therefore a light emission whose energy is used, in lithotripsy, for targeting and ablating the stone inside human body organ. Apart from medical usage, laser is used for optical disk drive, printer, barcode reader etc. What is the full form of LASER?

Read the following text and answer the following questions on the basis of the same: Laser: Electromagnetic radiation is a natural phenomenon found in almost all areas of daily life, from radio waves to sunlight to X-rays. Laser radiation - like all light - is also a form of electromagnetic radiation Electromagnetic radiation that has a wavelength between 380 nm and 780 nm is visible to the human eye and is commonly referred to as light. At wavelengths longer than 780 nm, optical radiation is termed infrared (IR) and is invisible to the eye. At wavelengths shorter than 380 nm, optical radiation is termed ultraviolet (UV) and is also invisible to the eye. The term "laser light" refers to a much broader range of the electromagnetic spectrum that just the visible spectrum, anything between 150 nm up to 11000 nm (i.e. from the UV up to the far IR). The term laser is an acronym which stands for "light amplification by stimulated emission of radiation". Einstein explained the stimulated emission. In an atom, electron may move to higher energy level by absorbing a photon. When the electron comes back to the lower energy level it releases the same photon. This is called spontaneous emission. This may also so happen that the excited electron absorbs another photon , releases two photons and returns to the lower energy state. This is known as stimulated emission. Laser emission is therefore a light emission whose energy is used, in lithotripsy, for targeting and ablating the stone inside human body organ. Apart from medical usage, laser is used for optical disk drive, printer, barcode reader etc. What is the range of amplitude of LASER?