Download An introduction to Optics

Optics
An introduction to Optics
Optics is the study of light and describes its behaviour and properties. Optics looks at light’s origin and it’s
propagation- which is how the light spreads out.
There are two branches of Optics:
Classic optics – The study of Geometrical Optics and Wave Optics.
Quantum Optics – Light on a quantized photons.
Optic’s History
Optics is a field of study that is more than 2000 years old. It started in Ancient Greece when the Ancient Greek
Philosophers began question the world around them and try and figure out what it was made of.
Galileo who live in 1500 BC invented the telescope which led to the microscope and theodolites- Optics was
expanding the horizons of the world around us. With the telescope they discovered that that our solar system is
Heliocentric instead of Geocentric, with microscopes they looked deeper into the world around them and with
theodolites they could measure the angles of the world around them.
20th century Optical inventions/discoveries
Amazing inventions using lasers in the 20th century were developed such as DVD players and now the more
modern and advanced Blue-Ray player which uses the stronger blue laser
instead of the weaker red laser.

The Photoelectric Effect:
An observation that many metals emit electrons when light shines upon them.
Electrons emitted in this manner may be called photoelectrons.

Blackbody Radiation:
A type of electromagnetic radiation within or surrounding a body in
thermodynamic equilibrium with its environment, or emitted by a black body (an
opaque and non-reflective body.

Spectral Lines:
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a
deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies.
Continuous Spectrum
Emission Lines
Absorption Lines
Sources of Light
Chemical energy is converted into light through Combustion
Nuclear energy is converted into light through
Fission or Fusion
Electrical energy is converted into light through Electricity
Chemical energy is converted into light without generating
heat through Chemolouminescence.
Terminology:
Transparent: Light goes through without being scattered.
Translucent: light goes through but is scattered.
Reflective: All light bounces back as it hits the surface.
Deflective: All light bounces back in random directions.
Absorbent: Some components of white light do not bounce back.
Opaque: No light goes through.
Refraction: is the change in direction of a wave due to a change in its transmission medium.
Properties of light:
Light travels in straight lines. It is invisible as long as it is not reflected in your eye.
Refraction:
Exp.1
Method: A glass pipe is placed in a fish tank.
n1 x sinθ1 = n2 x sinθ2
Angles are measured with respect to the line which is perpendicular to the interface. It is called the
normal.
When light travels from one medium--such as air, to another one of higher density--such as water,
usually the light ray bends toward the perpendicular line.
The quantitative law of refraction, called Snell´s law, was first worked out in 1621 by Willibrord Snell
(Dutch astronomer and mathematician).
Refractive Indices of Different Transparent Substanc
Refraction
Refraction is essentially a surface phenomenon. The phenomenon is mainly in governance to the law
of conservation of energy and momentum. Due to change of medium, the phase velocity of the
wave is changed but its frequency remains constant. This is most commonly observed when a wave
passes from one medium to another at any angle other than 90° or 0°. Refraction of light is the most
commonly observed phenomenon, but any type of wave can refract when it interacts with a
medium, for example when sound waves pass from one medium into another or when water waves
move into water of a different depth. Refraction is described by Snell's law, which states that for a
given pair of media and a wave with a single frequency, the ratio of the sines of the angle of
incidence θ1 and angle of refraction θ2 is equivalent to the ratio of phase velocities (v1 / v2) in the
two media, or equivalently, to the opposite ratio of the indices of refraction (n2 / n1):
In optics, refraction is a phenomenon that often occurs when waves travel from a medium with a
given refractive index to a medium with another at an oblique angle. At the boundary between the
media, the wave's phase velocity is altered, usually causing a change in direction. Its wavelength
increases or decreases but its frequency remains constant. For example, a light ray will refract as it
enters and leaves glass, assuming there is a change in refractive index. A ray traveling along the
normal (perpendicular to the boundary) will change speed, but not direction. Refraction still occurs
in this case. Understanding of this concept led to the invention of lenses and the refracting
telescope. (Wikipedia, 2014)
Main Lesson:
REFraCTION2
TOTAL INTERNAL REFLECTION:
Reflection is when light travels from one surface to another and bounces back.
We have seen, how a ray of light, passing from glass to air, bends away from the normal.
If we increase the angle of incidence, the angle of refraction increases too.
o
At a particular value of angle of incidence, the angle of refraction is 90 .
This particular angle of incidence is called the critical angle.
Above the critical angle we get total internal reflection. There is no transmission of light at
all.