PHY 11 - Light and Geometrical Optics Flashcards
What is the approximate speed of light in a vacuum ?
295 000 000 m/s
What is refraction of light dependent on ?
The density of the medium
e.g. water = low density and therefore minimum refraction
What is meant by the rarer medium in terms of light ?
The least dense medium
What happens to light when it passes from a rarer to a denser medium ?
It is refracted towards the normal (90º to the surface)
What happens to light when it passes from a denser to a rarer medium ?
It is refracted away from the normal (90º to the surface)
What is the difference between the angle of incidence and the angle of refraction ?
They are equal
Why do we see colour ?
Different wavelengths of light make up the visible portion of the light spectrum (the electro-magnetic spectrum)
Describe the two aspects of the theory of light
- Particulate - referring to a packet of energy called a photon e.g. used to describe the photoelectric effect
- Wavy - e.g. light interference and diffraction
Why does diffraction occur ?
When waves of light bend at the interface between two different media.
Describe the optical domain of the electromagnetic wave theory ?
It corresponds to the following range of wavelengths:
0.4µ< h (visible) < 0.8µ
(µ = microns = 10-6 metres)
What is an electromagnetic field ?
At every point of the field there are two perpendicular vectors:
E: Electrical field vector
B: Magnetic induction field vector
What is polarized light ?
The electromagnetic wave front is polarized in a straight line when E and B are fixed at all times.
Therefore, it is light that has waves in only 1 plane.
What is reflection in terms of light ?
The process by which light rays bounce back into a medium from a surface with another medium.
What is the difference between an incident and a refracted ray ?
The ray that arrives from the source is the incident ray, the reflected ray is the ray that bounces back
What are the laws of reflection ?
The angle of incidence equals the angle of reflection at normal.
What are spherical mirrors ?
They are non-plane mirrors which may have the reflecting surface concave (converges light) or convex (diverges light)
What is a vertex ?
The centre of a mirror
Describe the convention for lower and upper case letters in terms of light optics
Upper case: refer to a point
Lower case: refer to a distance
What is refraction ?
The bending of light as it passes from one transparent medium to another. This is caused by the different speeds of light in the two media
What is the relationship between wavelength and speed ?
Longer wavelengths travel faster in a medium than shorter wavelengths (ie. longer wavelengths are more subject to refraction)
What is dispersion of light ?
The separation of white light (ie. all colours together) into individual colours by differential refraction
What are the laws of refraction ?
- The incident ray, the refracted ray and the normal ray all lie in the same plane
- The path of the ray (incident and refracted parts) is reversible
What is the critical angle in terms of light optics ?
Explain why when looking at an object under water from above the surface, the object appears closer than it actually is ?
What is a lens ?
A transparent material which refracts light
What is the difference between converging and diverging lenses ?
Converging lenses refract toward the axis, diverging lenses refract away from the axis.
What are aberrations in terms of light optics ?
E.g. A nick or a cut in a convex lens might create a microscopic are of concavity, causing divergent light instead of convergent light. The image will be less sharp or clear as the number or sizes of aberrations increase.
