Reflection of light presentation

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Reflection & Diffraction

Reflection :- : 

Reflection :- Definition of Reflection. Laws of reflection. Critical Angle. Total internal reflection. Contents :-

Definition of Reflection “Reflection occurs when light changes direction as a result of "bouncing off" a surface like a mirror. " Normal Angle of incidence Angle of reflection This is an example of reflection of light.

1st Law of reflection : 

1st Law of reflection Angle of incidence = Angle of reflection Angle of reflection Angle of incidence

2nd Law of reflection : 

2nd Law of reflection The incident ray, the reflected ray and the normal all lie in the same plane.

Critical Angle : 

Critical Angle When the angle of refraction is 90, the incident angle is called the critical angle(C).

Total Internal Reflection : 

Total Internal Reflection An effect that combines both refraction and reflection is total internal reflection. When refraction angle exceeds 90º the light does not cross the surface.

Diffraction : 

Diffraction Definition of diffraction. Diffraction occurrence. Characteristics of Diffraction of waves. Diffraction of Electromagnetic Waves. Contents :-

Definition of Diffraction : 

Definition of Diffraction Waves are scattered when they pass through an aperture or are bent by passing from one medium to another .

Diffraction occurs with all waves.. : 

Diffraction occurs with all waves.. Sound waves. Water waves. Electromagnetic waves such as Visible light. X-rays. Radio waves .

Characteristics of Diffraction of waves: : 

Characteristics of Diffraction of waves: The frequency, wavelength and speed of the waves remains the same after diffraction. The direction of propagation and the pattern of the waves change. The effect of diffraction is most obvious when λ ≥ a, a = size of the aperture.

The amplitude of the part of the wave that spreads out is lower - because the energy is distributed over a bigger area. : 

The amplitude of the part of the wave that spreads out is lower - because the energy is distributed over a bigger area.

When λ < a …… : 

When λ < a …… Diffraction through a big aperture. The effect of diffraction is not obvious. The waves are bent only at the edges after passing the slit.

When λ ≥  a …. : 

When λ ≥  a …. Diffraction of a small aperture (about the size of the wavelength of the water wave). The effect of diffraction is obvious. The waves are circular and appear to originate from the small slit.

Diffraction of Electromagnetic Waves:- : 

Diffraction of Electromagnetic Waves:- Radio waves are used in radio and television to transmit audio and picture signal over long distance. Similar to other electromagnetic waves, radio waves also travel in straight line. For long and medium wavelength radio transmissions, they can diffract round obstacles like large buildings and hills, so radio reception on long and medium wave is quite good in hilly areas.

Slide 16: 

For Very High Frequency (VHF) for stereo radio and Ultra High Frequency waves (UHF) for TV transmissions (short wavelength), they do not diffract easily. Hence good reception of VHF and UHF is only possible over short distance from the transmitting towers and with the use of good aerials. These radio waves also diffract round the earth's curvature and are reflected by the ionosphere (a layer of charged particles above the atmosphere). This results in good and clear transmission of long and medium waves over long distances.