Case Study Questions for Class 12 Physics Chapter 8 Electromagnetic Waves
Question 1:
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.
Read the following case/passage and answer the following questions:
(i) What is the full form of LASER ?
(a) Light amplified by stimulated emission of radiation
(b) Light amplification by stimulated emission of radiation
(c) Light amplification by simultaneous emission of radiation
(d) Light amplified by synchronous emission of radiation
Answer
Answer:Option (b) is correct.
Explanation: The term laser is an acronym which stands for “light amplification by stimulated emission of radiation”.
(ii) The “stimulated emission” is the process of :
(a) release of a photon when electron comes back from higher to lower energy level.
(b) release of two photons by absorbing one photon when electron comes back from higher to lower energy level.
(c) absorption of a photon when electron moves from lower to higher energy level.
(d) None of the above Ans.
Answer
Answer:Option (b) is correct.
Explanation: 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.
(iii) What is the range of amplitude of LASER?
(a) 150 nm – 400 nm
(b) 700 nm – 11000 nm
(c) Both the above
(d) None of the above
Answer
Answer:Option (c) is correct.
Explanation: 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).
(iv) Lithotripsy is:
(a) an industrial application.
(b) a medical application.
(c) laboratory application.
(d) process control application.
Answer
Answer:Option (b) is correct.
Explanation: Laser emission is therefore a light emission whose energy is used, in lithotripsy, for targeting and ablating the stone inside human body organ.
(v) LASER is used in:
(a) optical disk drive.
(b) transmitting satellite signal.
(c) radio communication.
(d) ionization.
Answer
Answer:Option (a) is correct.
Explanation: An optical disc drive (ODD) is a disc drive that uses laser light or electromagnetic waves within or near the visible light spectrum as part of the process of reading or writing data to form optical discs.