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General ScienceMedium

The first working laser, a ruby laser, was built in 1960 by

  1. A.Charles Townes
  2. B.Theodore Maiman
  3. C.Dennis Gabor
  4. D.Arthur Schawlow

Correct answer

B. Theodore Maiman

Explanation

The correct answer is B, Theodore Maiman. Maiman built the first operating laser in 1960, using a rod of synthetic ruby, that is chromium ions in aluminium oxide, pumped by a flash lamp, and it emitted pulses of deep red light. Option A is wrong because Charles Townes built the first maser in 1954, which amplified microwaves rather than visible light, and he shared a Nobel Prize for the maser principle. Option C is wrong because Dennis Gabor invented holography and received the Nobel Prize for it in 1971; holography became practical only after the laser existed. Option D is wrong because Arthur Schawlow worked with Townes on the theory of the optical maser but did not build the first device. Fix 1954 maser, 1960 laser.

Read the full article: Photoelectric Effect, Lasers and Superconductivity Notes

Practice Questions

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Q1.General ScienceMedium

The photoelectric effect was first observed by which scientist?

  1. A.Albert Einstein
  2. B.Heinrich Hertz
  3. C.Max Planck
  4. D.Robert Millikan
Show answer
Correct answer: B. Heinrich Hertz

In 1887, while studying the sparks produced across a gap between two electrodes, Hertz noticed that the spark passed more easily when ultraviolet light fell on the electrodes, which was the first observation of the photoelectric effect; Hallwachs and Lenard then studied it systematically.

Q2.General ScienceMedium

Albert Einstein was awarded the Nobel Prize in Physics for 1921 mainly for

  1. A.The special theory of relativity
  2. B.The general theory of relativity
  3. C.His explanation of the photoelectric effect
  4. D.The discovery of the photon rest mass
Show answer
Correct answer: C. His explanation of the photoelectric effect

The citation for the prize refers to his services to theoretical physics and especially to his discovery of the law of the photoelectric effect, the equation in which the energy of a photon equals the work function plus the maximum kinetic energy of the emitted electron.

Q3.General ScienceMedium

The maximum kinetic energy of the photoelectrons emitted from a metal surface depends on

  1. A.The intensity of the incident light
  2. B.The frequency of the incident light
  3. C.The area of the illuminated surface
  4. D.The time for which light falls
Show answer
Correct answer: B. The frequency of the incident light

By Einstein's photoelectric equation, the photon gives energy equal to Planck's constant times the frequency, part of which is spent as the work function, so the maximum kinetic energy left with the electron rises with frequency and is independent of how bright the light is.

Q4.General ScienceEasy

The minimum energy required to eject an electron from the surface of a metal is called its

  1. A.Work function
  2. B.Stopping potential
  3. C.Ionisation energy
  4. D.Binding energy
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Correct answer: A. Work function

The work function of a metal is the least energy needed to free an electron from its surface, and it is equal to Planck's constant multiplied by the threshold frequency of that metal; caesium and potassium have low work functions, which is why they respond to visible light.

Q5.General ScienceEasy

The word LASER is an abbreviation for

  1. A.Light Absorption by Spontaneous Emission of Radiation
  2. B.Light Amplification by Stimulated Emission of Radiation
  3. C.Linear Amplification of Stored Energy by Radiation
  4. D.Light Alignment by Statistical Emission of Rays
Show answer
Correct answer: B. Light Amplification by Stimulated Emission of Radiation

The device works by stimulated emission, in which a photon passing an excited atom makes it fall to a lower level and emit a second photon identical in frequency, phase and direction, so one photon becomes two and the light is amplified.