LIGHTS AND OPTICS

Reflection

Refraction

Optical Instruments

THE NATURE OF LIGHTLight (along with all other forms of electromagnetic radiation) is a fundamental entity and physics is still snuggling to understand it.

Light may be defined as electromagnetic radiation, which is visible to the human eye. It is also applied to radiation having frequencies somewhat above and below the range human sight.Many of the properties of light can be explained on the theory that light is a transverse wave motion with both electrical and magnetic properties. This theory satisfactorily explains the variation in the velocity of light as it passes through different solid, liquids, and gases.

PROPERTIES OF LIGHT

SOURCES OF LIGHT

REFLECTION OF LIGHT

It is the turning back of light waves from a surface.

The amount of light an object reflects depends upon the kind of material it is made of, how well its surface is polished, and the angle at which the light strikes its surface.

REFLECTION

LAWS OF REFLECTIONBy laboratory experiment it may be shown that the

angle of reflection is equal to the angle of incidence. Furthermore, the reflected ray lies in the same plane as the incident ray and the normal to the reflecting surface at the point of reflection. These statements are called the LAWS OF REFLECTION.

The angle of incidence is equal to the angle of reflection.

The incident ray, the reflected ray, and the normal all lie in the same plane.

Normal

Angle of Incidence

It is a line drawn perpendicular to a line or plane.

It is the angle between the incident ray and the normal drawn to the point

of reflection.

Angle of Reflection

Plane of Incidence

the angle between the reflected ray and the normal drawn to the point of reflection.

the incident ray, reflected ray, and normal to the surface all lie in the same plane

Reflected Ray

Incident Ray

 It is the ray that represents the light reflected by the surface. 

It is a ray of light that strikes a surface. 

LAWS OF REFLECTION

surface normal

plane reflecting surface

Incident ray Reflected ray

90°

Angle ofincidence

Angle ofreflection

.Point of incidence

IMAGES IN A PLANE MIRROR

The Characteristics of an Image in a Plane Mirror are:

It is the same size as the

object

It is vertically erect

It is virtual

REFLECTION OF LIGHT

REFLECTION OF LIGHT

REFRACTION OF LIGHT

It is a phenomenon when a ray of light is transmitted obliquely through the boundary between two materials of unlike index of refraction, the ray bends.

The bending of light rays as they pass obliquely from one medium into another of different optical density, is a property of a transparent substance which is a measure of the speed of light through the substance.

REFRACTION

PARTIAL REFLECTIONand

PARTIAL REFRACTION

When light passes at an angle from air to glass, it immediately changes direction. Also, at the boundary between the air and the glass, but some are reflected according to the laws of reflection.

normal Incident ray

airglass

reflected ray

boundary

reflected ray

Diagram Of An Air/Glass Interface

r

i

R

REFRACTION OF LIGHT

INDEX OF REFRACTION

The speed of light in a vacuum (c) is 2.997 924 x 10⁸ m/s. In air, the speed of light is only about 0.000 87 x 10⁸ m/s less than in a vacuum. Thus the value 3.00 x 10⁸ m/s can be used for air or a vacuum.

INDEX OF REFRACTION

In other transparent mediums, such as water or glass, the speed is significantly smaller. It was a French scientist, Jean Foucault, who, in 1862, devised a method for measuring the speed of light in both air and water. He found that light travels in water at approximately three – quarters the speed it travels in a vacuum, i.e., at 0.75 c.

INDEX OF REFRACTION

Other materials produce different values, but the speed is always smaller than the speed of light in a vacuum. The term “optically dense” is used when referring to a medium in which the speed of light decreases.

INDEX OF REFRACTION

The ratio of the speed of light in a vacuum (c) to the speed of light in a given material (v) is called the index of refraction (n) of that material. That is,

n = c ⁄ v

INDICES OF REFRACTIONSubstances Index of refraction (n)

Vacuum 1.0000

Air (0°C, 101 kPa) 1.0003

Water 1.33

Ethyl alcohol 1.36

Quartz (fused) 1.46

Glycerin 1.47

Lucite or Plexiglass 1.51

Glass (crown) 1.52

Sodium chloride 1.53

Glass (crystal) 1.54

Ruby 1.54

Glass (flint) 1.65

Zircon 1.92

Diamond 2.42

LAWS OF REFRACTION

Although the phenomenon of refraction had been known for centuries, it was not until 1621 when Willebrod Snell, a Dutch mathematician, determined the exact relationship between the angle of incidence and the angle of refraction. This discovery enabled scientists to predict the direction of a ray light would take in various media. Snell’s Law says:

sin i/sin R = constant

LAWS OF REFRACTION

It has been found that the Snell’s Law constant and the index of refraction (n)is one and the same thing. Consequently, the Snell’s Law relationship may be written as:

sin i/sin R = n

LAWS OF REFRACTIONThe ratio of the sine of the

angle of incidence to the sine of the angle of refraction is constant (also known as Snell’s Law).

The incident ray and the refracted ray are on opposite sides of the normal ray at the point of incidence, and all three are in the same plane.

PRISM

It can be used to dispose light into its various colors, because the index of refraction of a material varies with wavelength, different colors of light refract differently. In nearly all materials, red is refracted least and blue is refracted most.

HOW A PRISM WORKS TO MAKE A RAINBOW COLORS

CONVERGING LENSES

DISPERSION OF LIGHT