Properties of light

Reflection of Light

Reflection is the turning back of the light from the surface it hits. Incoming and reflected lights have same angle with the surface. If the surface reflects most of the light then we call such surfaces as mirrors.

Laws of Reflection

First law of reflection states that; Incident ray, reflected ray and Normal to the surface lie in the same plane.

Angle of incident ray is equal to the angle of reflection ray.

Plane Mirrors and Image Formation in Plane Mirrors

If the reflecting surface of the mirror is flat then we call this type of mirror as plane mirrors. Light always has regular reflection on plane mirrors.

First look at picture and then follow the steps one by one.

In plane mirrors, we use the laws of reflection while drawing the image of the objects. As you see from the picture we send rays from the top and bottom of the object to the mirror and reflect them with the same angle it hits the mirror. The extensions of the reflected rays give us the image of our object. The orientation and height of the image is same as the object. In plane mirrors always virtual image is formed.

Curved Mirrors

We call these types of mirrors also spherical mirrors because they are pieces of a sphere. If the reflecting surface of the mirror is outside of the sphere then we call it convex mirror and if the reflecting surface of it is inside the sphere then we call it concave mirror.

Center of Curvature: As you can understand from the name it is the center of the sphere which the mirror is taken from. It is denoted by C in the diagrams.

Principal Axis: Line coming from the center of the sphere to the mirror is called as principal axis.

Vertex: It is the intersection point of the mirror and principal axis. We show it with the letter V in ray diagrams.

Focal Point: For concave mirrors and thin lenses rays coming parallel to the principal axis reflects from the optical device and pass from this point. For convex mirrors and thick lenses rays coming from this point or appear to coming from this point reflect parallel to the principal axis from the optical device. Another explanation for this term is that, it is the point where the image of the object at infinity is formed. It is denoted with the letter F or sometimes f in ray diagrams.

Radius of Curvature: It is the distance between center of the sphere and vertex. We show it with R in ray diagrams.

Mirror Equations of Curved Mirrors

Refraction

When light passes from one medium to another medium velocity of it changes and so, its direction changes. We call this change in the direction of light refraction.

Refractive Index

It is the ratio of the speed of light in vacuum to the speed of the light in given medium. Refractive index of medium A is given below;

The Laws of Refraction

1. Incident ray, reflected ray, refracted ray and the normal of the system lie in the same plane.
2. Incident ray, coming from one medium to the boundary of another medium, is refracted with a rule derived from a physicist Willebrord Snellius. He found that there is a constant relation between the angle of incident ray and angle of refracted ray. This constant is the refractive index of second medium relative to the first medium. He gives the final form of this equation like;

Critical Angle and Total Reflection

According to the angle of incident ray, at one point it does not refract but goes parallel to the boundary of the mediums. We called this angle as critical angle. If the angle of incident ray is larger than the critical angle then it does not refract but it does total reflection.

 

 Reference:

 http://www.physicstutorials.org/

The Eye is like a Camera

Blue sky

The blue color of the sky is caused by the scattering of sunlight off the molecules of the atmosphere. This scattering, called Rayleigh scattering, is more effective at short wavelengths (the blue end of the visible spectrum). Therefore the light scattered down to the earth at a large angle with respect to the direction of the sun's light is predominantly in the blue end of the spectrum.

Note that the blue of the sky is more saturated when you look further from the sun. The almost white scattering near the sun can be attributed to Mie scattering, which is not very wavelength dependent.

 
 

Pasted from <http://hyperphysics.phy-astr.gsu.edu/HBASE/atmos/blusky.html>

 
 

Red sunset

Sunsets are reddened because for sun positions which are very low or just below the horizon, the light passing at grazing incidence upon the earth must pass through a greater thickness of air than when it is overhead. Just before the sun disappears from view, its actual position is about a diameter below the horizon, the light having been bent by refraction to reach our eyes. Since short wavelengths are more efficiently scattered by Rayleigh scattering, more of them are scattered out of the beam of sunlight before it reaches you. Aerosols and particulate matter contribute to the scattering of blue out of the beam, so brilliant reds are seen when there are many airborne particles, as after volcanic eruptions.

 
 

The equivalent phenomenon can be seen at sunrise

 
 

Pasted from <http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/redsun.html>

 
 

How a Rainbow is Formed

10 Great Motivational Quotes

Light

• Our primary source of light is the sun.
  
• Light travels in straight lines at a speed of 186,000miles per second.
  
• *Light waves travel faster than sound waves!
  
• Light energy from the sun travels through space , reaches earth, and some of it turns to heat energy and warms the earth's air.
  
• Light from the sun also travels to the cells of green plants (producers) and is stored as energy.
  
• When light reaches an object, it is absorbed, reflected, or passes through it.
  

 

SOURCES OF LIGHT

• SUN=warms air, water, and land.
  
• Fire=provides heat, light, and cooking fuel.
  
• Lightning
  
• Firefly
  
• Flashlight
  
• Light bulb
  
• Laser beams
  
• Optical
  
  telephone
  
  fibers
  
  *Traffic lights
  
  

 

EXAMPLE OF TRANSPARENT OBJECTS:

• The windows on a school bus,
  
• A clear empty glass,
  
• A clear window pane,
  
• The lenses of some eyeglasses,
  
• Clear plastic wrap,
  
• The glass on a clock,
  
• A hand lens,
  
• Colored glass…
  
• ALL of these are transparent. Yes, we can see through them because light passes through each of them.
  

 

EXAMPLE OF TRANSLUCENT OBJECTS:

• Thin tissue paper,
  
• Waxed paper,
  
• Tinted car windows,
  
• Frosted glass,
  
• Clouds,
  
• All of these materials are translucent and allow some light to pass but the light cannot be clearly seen through.
  

 

EXAMPLE OF OPAQUE OBJECTS:

• Heavy weight paper,
  
• Cardboard
  
• Aluminum foil,
  
• Mirror, bricks, buildings,
  
• Your eyelids and hands,
  
• Solid wood door,
  
• All of these objects are opaque because light cannot pass through them at all.
  
• They cast a dark shadow.
  

 

WHAT IS REALY LIGHT? . .Electromagnetic wave radiation

• Light waves are three dimensional.
  
• Light waves vibrate in all planes around a center line.
  
• The waves have high points called "crests."
  
• Waves also have low points called "troughs."
  
• *The distance from one crest to the next crest is called a "wavelength."
  
• *The number of waves passing a given point in one second is called the "frequency."
  

 

 

ELECTROMAGNETIC WAVE

• Electromagnetic radiation can be described as a stream of photons. Each photon traveling in a wave-like pattern, moving at the speed of light and carrying some amount of energy.
  
• The only difference amongst radio waves, visible light, and gamma-rays is the amount of energy of the photons. Radio waves have photons with low energies. Microwaves have a little more energy than radio waves. Gamma-rays and cosmic rays have highest energy waves and are the deadliest.