# VT Level III Questions- Answers

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1. What property of mirrors allows them to change the direction of light?
• a) Refraction
• b) Diffraction
• c) Reflection
• d) Dispersion
2. Which type of mirror provides an enlarged field of view of the reflected image?
• a) Flat
• b) Convex
• c) Concave
• d) Parabolic
3. Where is the reflecting focal point of a concave or spherical mirror located?
• a) In front of the mirror
• b) Behind the mirror
• c) At the center of the mirror
• d) At the top of the mirror
4. What happens to light when it is projected onto a spherical mirror normal to the curve of the surface?
• a) It is absorbed by the mirror
• b) It is refracted away from the mirror
• c) It is focused slightly in front of the mirror
• d) It passes through the mirror unaffected
5. How does a concave mirror reflect light when a point light source is placed at its focal point?
• a) It reflects the light back towards the source
• b) It refracts the light away from the source
• c) It reflects the light parallel to the normal of the curve
• d) It focuses the light at a point in front of the mirror
6. Which type of prism deflects light rays by 90 degrees?
• a) Right angle prism
• b) Porro prism
• c) Convex prism
• d) Concave prism
7. What is the angle above which all light is reflected known as?
• a) Incidence angle
• b) Refractive angle
• c) Critical angle
• d) Reflection angle
8. What is the primary function of a porro prism?
• a) To produce a 90 degree reflection
• b) To separate frequencies of a chromatic light source
• c) To change the orientation of the image produced by light rays
• d) To provide an enlarged field of view of the reflected image
9. How do prisms separate the frequencies of a chromatic light source?
• a) By refraction
• b) By diffraction
• c) By dispersion
• d) By reflection
10. Why do the higher frequency portions of the spectrum emerge from the base of the prism?
• a) Because the refractive indices of the materials are higher at the base
• b) Because the refractive indices of the materials are lower at the base
• c) Because the index of refraction changes with the frequency of the light
• d) Because the angle of incidence is greater at the base
11. What is the most frequent reason for reduced vision acuity?
• a) Glaucoma
• b) Cloudy ocular media
• c) Uncorrected refractive error
• d) Macular degeneration
12. How is vision conventionally graded?
• a) By measures of contrast sensitivity
• b) By the size of the visual objects
• c) By measures of visual acuity
• d) By the brightness of the background
13. What is the typical contrast percentage for a vision acuity chart with black letters?
• a) Less than 20%
• b) Between 50% to 60%
• c) Greater than 85%
• d) Exactly 100%
14. What is contrast sensitivity a better predictor of, compared to vision acuity?
• a) Brightness perception
• b) Object size perception
• c) Functional vision performance
• d) Color perception
15. At what spatial frequencies is the contrast sensitivity of the normal visual system highest?
• a) Below 2 cycles per degree
• b) Between 6 to 8 cycles per degree
• c) Between 2 to 6 cycles per degree
• d) Above 8 cycles per degree
16. Which method presents letters of constant size with decreasing contrast to measure contrast sensitivity?
• a) Pelli-Robson ™ letter sensitivity chart
• b) Weber contrast method
• c) Michelson contrast method
• d) Contrast threshold method
17. What does a difference in far vision acuity versus near vision acuity indicate?
• a) Need for cataract surgery
• b) Need for glaucoma treatment
• c) Potential refractive correction benefit
• d) Development of macular degeneration
18. Which condition is NOT listed as a reason for reduced vision acuity?
• a) Glaucoma
• b) Scarred cornea
• c) Diabetic retinopathy
• d) Nearsightedness
19. What is the angular measure of the smallest detail that can be resolved when presented with high contrast?
• a) Vision threshold
• b) Visual acuity
• c) Spatial frequency
• d) Contrast threshold
20. What aspect of the visual system does contrast sensitivity primarily depend on?
• a) Lens curvature
• b) Retinal pigment density
• c) Size of the pupil
• d) Neural processing
21. What is the goal when choosing lighting for automated inspection and machine vision applications?
• a) To increase the brightness of the environment
• b) To decrease the contrast between discontinuities
• c) To optimize contrast and reduce signal processing complexity
• d) To minimize the spectral sensitivity of sensors
22. Which type of light source is ineffective during direct visual testing but recommended for automated inspection?
• a) Incandescent
• b) Luminescent
• c) Polarized
• d) Solar
23. What is critical in automated inspection due to light sensors’ limited ability to adapt to differing levels of illumination?
• a) Consistent illumination
• b) Dynamic illumination
• c) Variable illumination
• d) Intermittent illumination
24. Which characteristic of a test material determines the type of lighting geometry and light source for inspection?
• a) Reflective, absorptive, and transmissive characteristics
• b) Temperature and pressure
• c) Electrical conductivity
• d) Chemical composition
25. What type of light source is commonly used for inspecting nonselective absorptive materials?
• a) Condenser reflector
• b) Spot projector
• c) Diffuse light source
• d) Collimated light source
26. Which lighting technique floods the area of interest with light to minimize shadow formation?
• a) Side illumination
• b) Front illumination
• c) Back illumination
• d) Top illumination
27. Which type of light source is characterized by emission due to thermal excitation of atoms or molecules?
• a) Solar
• b) Luminescent
• c) Incandescent
• d) Coherent
28. How is luminescent light different from incandescent light sources?
• a) It emits light without thermal excitation
• b) It emits light with a broader spectrum
• c) It emits light with a higher degree of phase coherence
• d) It emits light with a more monochromatic nature
29. What is the primary characteristic of coherent light?
• b) Non-directional propagation
• c) Parallel alignment of rays
• d) Random phase coherence
30. Which optical technique uses polarized light to measure interference patterns for assessing test objects?
• a) Diffraction
• b) Refraction
• c) Birefringence
• d) Dispersion
31. What is the term used to describe discontinuities formed during the metal casting process due to imperfect fusion between two streams of metal?
• a) Cold Shut
• b) Hot Tears
• c) Blowholes
• d) Porosity
32. Which type of discontinuity may result from uneven cooling in thin sections or corners that adjoin heavier masses of metal?
• a) Cold Shut
• b) Pipe
• c) Hot Tears
• d) Blowholes
33. Gas porosities in castings are caused by the accumulation of gas bubbles during solidification. What term describes the non-metallic inclusions usually found in ferrous alloys?
• a) Cold Shut
• b) Hot Tears
• c) Blowholes
• d) Nonmetallic Inclusions
34. What type of discontinuity may appear as seams in the rolled ingot and can be conical, wide at the surface, and tapering internally?
• a) Cold Shut
• b) Pipe
• c) Hot Tears
• d) Blowholes
35. What is the term used to describe the rounded cavities caused by the accumulation of gas bubbles in molten metal as it solidifies?
• a) Cold Shut
• b) Pipe
• c) Hot Tears
• d) Porosity
36. What is undercut in welding?
• a) A groove formed at the toe or root of a weld
• b) The complete filling of the root of the weld joint with weld metal
• c) The melting away of base metal at the root of a weld
• d) The reduction of base metal thickness due to excessive weld metal
• Answer: c) The melting away of base metal at the root of a weld
37. Which standard specifies that undercut should be less than 0.8 mm deep in completed welds?
• a) AWS D1
• b) ASME Boiler and Pressure Vessel Code
• c) ASTM International
• d) ISO 9001
• Answer: b) ASME Boiler and Pressure Vessel Code
38. What is the consequence of inadequate joint penetration in welding?
• a) Increase in base metal thickness
• b) Improved fatigue strength of the joint
• c) Reduction in joint strength, particularly fatigue strength
• d) Enhancement of joint ductility
• Answer: c) Reduction in joint strength, particularly fatigue strength
39. Which tool is recommended for visually detecting surface cracks in welding?
• a) High-power microscope
• b) 5× magnifying lens
• c) Ultrasonic testing device
• d) Infrared camera
• Answer: b) 5× magnifying lens
40. What causes arc strikes in welding?
• a) Poorly connected welding ground clamp
• b) Insufficient weld metal
• c) Inadequate base metal thickness
• d) Lack of joint penetration
• Answer: a) Poorly connected welding ground clamp
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3. Answer: a) In front of the mirror
4. Answer: c) It is focused slightly in front of the mirror
5. Answer: c) It reflects the light parallel to the normal of the curve
6. Answer: a) Right angle prism
8. Answer: d) To provide an enlarged field of view of the reflected image
10. Answer: c) Because the index of refraction changes with the frequency of the light
11. Answer: c) Uncorrected refractive error
12. Answer: c) By measures of visual acuity
13. Answer: c) Greater than 85%
14. Answer: c) Functional vision performance
15. Answer: c) Between 2 to 6 cycles per degree
16. Answer: a) Pelli-Robson ™ letter sensitivity chart
17. Answer: c) Potential refractive correction benefit