• Is the bending of a wave when it enters a medium where it's speed is different

• Amount of bending depends quantitatively by Snell's Law

Sin θ v = Sin θ v

Less optically denser More optically denser

More optically denser Less optically denser

1 1 2 2

Fog Brow

Upside down Rainbow

Glory

• Refraction has many applications in optics and technology.

• Some of the important ones are:

SpectacleCamera

Telescope

Prism to split light for spectrograph

Light Liquid Display

• Spectacle Lens

• Cameras

• Telescopes

• Microscope

• Liquid crystal displays

• In the past, people used to paint portraits in order to record images like landscapes, people etc.

• However , this was a long and tedious process as it took a long time to complete.

• It was until the invention of a revolutionary device that truly transformed how people conceive of the world

• Photography lets us capture moments in time and preserve them for years to come

• It was the Camera.

• Basically, a camera is made of three fairly simple elements

• By calibrating and combining these elements , they record a crisp, recognizable image.

• In this respect, it resembles an eye

Optical Element—Lens Chemical Element—Film

Mechanical Element—Camera Body

Optical Element—Lens Chemical Element—Film

Mechanical Element—Camera Body

Lens:A curved piece of glass

As light travels from one medium to another, it changes speed. Light travels more quickly through air than it does through glass, so the lens slows it down.

When light waves enter apiece of glass at an angle, one part of the wave will reach the glassbefore another and so willstart slowing down first.

When light waves enter a piece of glass at an angle, one part of the wave will reach the glass before another and so will start slowing down first.

Because the left wheel is briefly moving more quickly than the right wheel, the shopping cart turns to the right as it moves onto the grass.

This is like pushing a shopping cart from pavement to grass, at an angle .The right wheel hits the grass first and so slows down while the left wheel is still on the pavement.

The effect on light is the same – as it enters the glass at an angle, it bends in one direction.

This means rays of light passing through will bend toward the center of the lens on entry.

In a standard converging, or convex lens, one or both sides of the glass curves out.

The effect on light is the same – as it enters the glass at an angle, it bends in one direction.

• A real image is formed as a result • The nature of this real image varies depending on how the light travels through the lens

• It depends on two major factors: 1. The angle of the light beam's entry into the lens 2. The structure of the lens

Angle of light entry• Changes according to the distance of subject and lens

•Enter at a shaper angle•Exit at a more obtuse angle

•Enter At a more obtuse angle•Exit At a sharper angle

As a result , light beams from a closer point converge farther away from the lens than light beams from a point that's farther away.

• Therefore, the real image of a closer object forms farther away from the lens than the real image from a more distant object.

Lenses• Lens with a rounder shape (a center that extends out

farther) will have a more acute bending angle.• Curving the lens out increases the distance between

different points on the lens.

•This increases the amount of time that one part of the light wave is moving faster than another part, so the light makes a sharper turn.

• The previous phenomenon can be observed with a simple experiment.

1. Light a candle in the dark, and hold a magnifying glass between it and the wall

2. An upside down image of the candle will be formed If the real image of the candle does not fall directly on the wall, it will

appear blurry. The light beams don't converge at this point.

3. To focus the image, move the magnifying glass closer or farther away from the candle.

• Most vision problems occur when the eye cannot focus the image onto the retina.

• Here are a few of the most common problems: 1. Myopia (nearsightedness)

2. Hyperopia (farsightedness)

3. Astigmatism

4. Presbyopia

• One of the most common physical ailments that people suffer from is poor vision.

• The Human eye is constructed like a camera with clear lens at the front and light-sensitive tissue at the rear which has photographic functions

• If one of these components is not precisely the correct shape, then light that falls on the eye will not be focused correctly.

• Light from distant objects gets focused in front of the retina rather than on it

Causes• Usually happens when the eyeball is too long• Sometimes caused by too much focusing power in the

lens system. Result • Person can see close-up objects clearly, but distant

objects are blurry.

• Light gets focused in back of the retina rather than on it.Causes• Usually happens when the eyeball is too short or when

the focusing power of the lens system is too weak. Result • The person can see distant objects clearly, but close-up

objects are blurry

• Watch the video:

• Are frames bearing lenses worn in front of the eyes• Normally made of plastic to ensure safety

Uses • Vision correction• Eye protection• UV rays protection• Or decorative purpose…

• 1st century Emperor Nero watched the gladiatorial games using an emerald as a corrective lens

• 9th century Corrective lenses were used by Abbas Ibn Firnas in the, who had devised a way to produce very clear glass which is the ‘reading stone’.

• 1284in Italy, Salvino D'Armate is credited with inventing the first wearable eye glasses

• 1727 The modern style of glasses was developed in 1727 by the British optician Edward Scarlet.

• Refraction error is an error in the focusing of light by the eye which led to reduced visual sharpness

• The two most common ones are myopia and hyperopic as mentioned before

• Therefore, glasses are used to correct refractive errors of the eye by modifying the focal length of the lens

Compensating for myopia using a concave lens Restoring of vision with convex lens.

• Curiosity was one of an innate nature of humanity

• When Early Man could finally understand the occurrences around him on Earth , he began to observe the pitch-black void above him intently and asked himself,” What is that? Are there gods and angels dwelling in this twinkling dots”.

• Since the invention of telescope, mankind was able to explore the universe and the far-fetched concept of astronomy

soon materialized

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• A telescope is a device used to magnify distant objects • URL:

http://videos.howstuffworks.com/hsw/23389-astronomy-telescopes-video.htm

• Contrary to the popular belief that the telescope magnified light, the telescope merely gathered light in order to create a brighter and clearer image

• By using the simple concept of refraction, the telescope used multiple lens to focus the image.

• A telescope may sound like a complicated device but it is composed of two simple items

1. Objective lens : Collects lots of light from a distant object and brings that light to a point or focus.

2. Eyepiece lens : Takes the bright light from the focus of the objective lens and magnifies it to take up a large portion of the retina.

Drag bar to see the light inside

• Light is refracted into focus as it enters the objective lens • The eyepiece magnifies the bright image and spread it over our retina.

1. How well it can collect the light • Affected by the diameter of the lens or mirror -- the aperture -- that is

used to gather light. • The larger the aperture, the more light the telescope collects and

brings to focus, and the brighter the final image.

2. How much it can magnify the image • Depends on the combination of lenses used.• Affected by the type of eyepiece* Drag the bar to see the light beingmagnified as it traveled throughthe telescope

Diagram of a Newtonian reflector showing the light path inside.

• Throughout the history, mankind had been plagued by various of diseases especially the incurable or contagious ones.

• One such example was the bubonic plague which precipitated in one of the most notorious pandemic—Black Death

• Another notable epidemics are the smallpox and tuberculosis which claimed the lives of millions of people.

Illustration of the Black Death

What led to our success in developing new and powerful drugs?

• It was the invention of microscope that allow us to study the nature of various micro-organisms and learn more about them.

• Equipped with this knowledge, we are able to pinpoint their weakness and invented new drugs to combat them.

• Microscopes can magnify objects up to 1,000 times, revealing microscopic details

1021

The properties of magnifying glass are first described by an Arabic physicist, Ibn al-Haytham

1609

Galileo develops a compound microscope witha convex and a concave lens.

1931

Ernst Ruska built the first electron microscope.

1951

Erwin Wilhelm Müller invents the field ion microscope and is the first to see atoms.

Gerd Binnig and Heinrich Rohrer develop the scanning tunneling microscope (STM).

1981

• Gather light from a tiny area of a thin, well-illuminated specimenusing small and spherical objective lens with smaller focal length

• The objective lens brings the image of the object into focus at a short distance within the microscope's tube through refraction (Real)

• The image is then magnified by a second lens, called an ocular lens or eyepiece, as it is brought to your eye. (Virtual)

Object

Objective lens

• Related to focal length • Affected by:1. Can be controlled with the focus knobs2. Thickness of the cover glass on the specimen slide : Can be too

thick for the objective lens.

• Click on the any button and then click web preview to see how the distance of eyepiece affect the image

• URL:http://demonstrations.wolfram.com/RayDiagramsForMicroscopeAndTelescope/

• Video: How to use an optical Microscope • URL:

http://videos.howstuffworks.com/hsw/17165-how-to-use-a-microscope-the-optical-microscope-video.htm

• Activity: Made a Simple Microscope

1. Get two magnifying glasses and a sheet of printed paper. 2. Hold one magnifying glass a short distance above the paper. The image of the print will look a little bit larger. .

3. Place the second magnifying glass between your eye and the first magnifyingglass. The print now appear larger.