Visual Inspection and Basics - Module 2 - Part 1 Flashcards
What is light? And what concept is most suitable to describe it for NDT?
Scientists are still trying to define this!
Photon concept; light is made up of photon energy. Photons are like packets of energy that have some of the same characteristics of wave motion.
A wavelength is defined as…
…the distance between similar points on the wave form. Often referred to by a character from the Greek alphabet, λ (pronounced lambda).
Wavelength is important to visual inspection because it describes the ____ of light.
Colour.
The electromagnetic spectrum represents…
…all of the radiated electromagnetic energies including X-rays and radio waves.
The range of visible light is from approximately…
…400 nm to 700 nm. It is important to note that not everyone can perceive this entire range.
Definition: White light
Light that contains all the wavelengths of visible light at approximately equal intensities, as in sunlight or the light from white-hot solids.
When we see black…
no electromagnetic waves in the visible portion of the spectrum get to our eyes.
Contrast is…
the difference in colour and/or brightness of objects within our field of view. Occurs when light strikes the surface of a part (reflected or absorbed).
Why is contrast important for NDT?
The human eye is very sensitive to contrast, so it is important to create conditions that maximize contrast. This is usually done by cleaning the part to be inspected.
What types of surfaces tend to reflect more light?
Smooth or polished.
What types of colours tend to reflect more light? Absorb more?
Light colours.
Dark colours.
Inverse Square Law
The intensity of the light decreases as the distance from the source increases, or the farther away the light is the dimmer it appears.
The relationship of intensity and distance is defined by the formula:
S.I. = I/D^2 S.I. = Light intensity at the surface I = Original light intensity D = proportional increase in distance (new distance/original distance) *lux
The relationship between light intensity and distance is…
Doubling the distance from the light to the surface cuts the intensity by…
…exponential.
…a quarter.
Lambert’s Cosine Law
S.I.=I/D^2 x Cos Ɵ
S.I. = Light intensity at the surface I = Original light intensity D = proportional increase in distance (new distance/original distance) Ɵ = Angle that of the surface the light strikes
