CHAPTERS-16 &17Light

1. Electromagnetic waves

2. Human eye and color

3. Reflection and Image Formation

4. Refraction of Light

5. Lenses and Image Formation

6. Focusing Light with Curved mirrors

7. Eyeglasses, Microscopes, and Telescopes

Everyday Phenomenon:

Rainbows and Laser Refractive Surgery

Outline:

Electromagnetic Waves

• An electromagnetic wave consists of time-varying electric and magnetic fields, in directions perpendicular to each other as well as to the direction the wave is traveling.

There is a wide spectrum of frequencies and wavelengths of electromagnetic waves.

– Different types of electromagnetic waves have different wavelengths and frequencies.

– Together they form the electromagnetic spectrum.

How do our eyes distinguish color?

– Light is focused by the cornea and lens onto the retina.– The retina is made up of light-sensitive cells called rods and cones.– Three types of cones are sensitive to light in different parts of the

spectrum.

How Are Light Rays Related to wavefronts?

Wavefronts are perpendicular to the rays.

Reflection

The Law of Reflection

The angle of incidence = The angle of reflection.

ri

How Are Images Formed by a Plane Mirror?

How Are Images Formed by a Plane Mirror?

How tall must a plane mirror be in order for you to view your full height reflected in it?

a) Half your height.b) Three-quarters of your height.c) A little shorter than your height.d) Exactly your height.e) A little taller than your height.

Since the light reaching your eyes from your feet would be reflected from a point on the mirror exactly halfway between your feet and your eyes, you would be able to view your feet (and all points between your feet and your eyes) in a mirror that was half as tall as you.

Q7

Refraction of Light

Definition Of The Index Of Refraction

The index of refraction n of a material is the ratio of the speed c of light in a vacuum to the speed v of light in the material:

Law of Refraction

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Apparent Depth of Fish Is Smaller Than Actual Depth Due to Refraction

Total Internal Reflection

Why a Diamond Sparkles?

Why does a diamond exhibit such brilliance? And why does a diamond lose much of its brilliance when placed under water?

Optical Instruments

Many optical instruments, such as binoculars, periscopes, and telescopes, use glass prisms and total internal reflection to turn a beam of light through 90° or 180°.

Prism and Spectrum of Colors

Dispersion of Light

Rainbow

Primary Rainbow

Water droplet disperses the light into colors.

Secondary Rainbow

Colors are reversed and less intense.

Focal Point (F) and Focal Length (F)

Ray Diagram

Ray Diagram

Diverging or Negative lens:Focal Point (F) and Focal

Length (f)

Ray Diagram for Diverging Lens

Lens Equation

Lens Equation and Magnification, m

E6

Optical Instruments

• Human eye and Vision Defects

• Camera

• Eyeglasses

• Microscope

• Telescope

Nearsighted Eye, Myopia

Nearsightedness: can see only nearby objects clearly.Negative Lens Is Used to Correct Nearsightedness.

Positive Lens Is Used to Correct Farsightedness

Farsightedness: can see only far objects clearly.

How Does a Microscope Work?

• Used to view small things nearby.

• Consists of two positive lenses, objective and eyepiece.

• Final image is magnified and inverted.

• Ray diagram can be used to illustrate the image formation.

Ray Diagram For Microscope

A laboratory microscope has 3 or 4 objective lenses.

Astronomical Telescope