Laser Beam Machining Ppt Download For Mac

Posted on 18-09-2021 by admin

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Manufacturing Processes Multiple Choice Questions on “Laser Beam Machining – 2”.

1. When coming back to normal state from excited state, electron releases _____
a) proton
b) anti-proton
c) positron
d) photon
Answer: d
Clarification: On reaching the higher energy level, the electron reaches an unstable energy band. And it comes back to its ground state within a very small time by releasing a photon. This is called spontaneous emission.

2. In population inversion, no of electrons in _____ are more as compared to numbers of electrons in _____
a) quasi-stable state, ground state
b) meta-stable state, ground state
c) meta-stable state, quasi-stable state
d) mono-stable state, ground state
Answer: b
Clarification: Sometimes such change of energy state puts the electrons in a meta-stable energy band. Instead of coming back to its ground state immediately (within tens of ns) it stays at the elevated energy state for micro to milliseconds. In a material, if more number of electrons can be somehow pumped to the higher meta-stable energy state as compared to the number of atoms at ground state, then it is called “population inversion”.

3. In laser beam machine, one end of the glass is_____
a) open
b) blocked with a 10% reflective mirror
c) blocked with a 75% reflective mirror
d) blocked with a 100% reflective mirror
Answer: d
Clarification: The gas, called lasing medium is enclosed in a cylindrical glass vessel. One end of the glass is blocked with a 100% reflective mirror and the other end is having a partially reflective mirror.

4. In laser beam machining, electrons are excited by _____
a) high temperature steam
b) flash lamps
c) flash torch
d) cathode ray tube
Answer: b
Clarification: Population inversion can be carried out by exciting the gas atoms or molecules by pumping it with flash lamps. Then stimulated emission would initiate lasing action. Stimulated emission of photons could be in all directions.

5. The photons emitted in the _____ direction form a laser beam.
a) vertical
b) horizontal
c) longitudinal
d) lateral
Answer: c
Clarification: Most of the stimulated photons, not along the longitudinal direction would be lost and generate waste heat. The photons in the longitudinal direction would form coherent, highly directional, intense laser beam.

6. How many types of lasers are there?
a) 2
b) 3
c) 4
d) 5
Answer: a
Clarification: Many materials can be used as the heart of the laser. Depending on the lasing medium lasers are classified as:
• Solid-state laser
• Gas laser.

7. How many types of solid state lasers are there?
a) 2
b) 3
c) 4
d) 5
Answer: b
Clarification: Solid-state lasers are commonly of the following type:
• Ruby which is a chromium – alumina alloy having a wavelength of 0.7 μm
• Nd-glass lasers having a wavelength of 1.64 μm
• Nd-YAG laser having a wavelength of 1.06 μm
These solid-state lasers are generally used in material processing.

8. Lasers can be operated in _____ modes
a) 2
b) 7
c) 8
d) only one
Answer: a
Clarification: Lasers can be operated in
• continuous mode, or
• pulsed mode
Typically CO₂ gas laser is operated in continuous mode and Nd – YAG laser is operated in pulsed mode.

9. Helium-Neon is a gas laser.