Refraction

1
Refraction

• Lee Zi Jing
• 3i3 (13)

2
What is refraction?

• Refraction is the change in direction of a light
  wave due to a change in speed.
• This usually occurs as light passes through
  materials of different refractive index.
• This causes a change in speed and hence a
  resulting change in direction.

3
Snells law

• Snells law, also know as Snell-Descarte law, is
  a formula used to describe the relationship
  between the angle of incidence and refraction.
• v velocity, SI units are m/s
• n refractive index, which is unitless

4
(No Transcript)
5
Spectacles

• Corrective lenses are used to correct refractive
  errors of the eye.
• They modifying the effective focal length of the
  lens in order to alleviate the effects of
  conditions such as nearsightedness (myopia),
  farsightedness (hyperemia) or astigmatism.

6
Myopia

• Myopia causes far objects to appear blurred but
  near objects are seen clearly.
• Myopic eyeglasses have concave lenses, correcting
  the refraction error by moving the image of the
  distant objects backward onto the retina.

7
Hyperopia

• Hyperopia causes near objects to appeared blurred
  but far objects are seen clearly.
• Hyperopia glasses have convex lenses.
• They correct the refraction errors by moving the
  image of a distant object forward onto the retina.

8
Refracting telescope

• A refracting telescope is a type of optical
  telescope that uses a lens as its objective to
  form an image.
• The refracting telescope design was originally
  used in spy glasses and astronomical telescopes
  but is also used for long telephoto camera
  lenses.

9
Refracting telescope

• The objective in a refracting telescope refracts
  or bends light.
• This causes parallel light rays to converge at a
  focal point.
• The telescope converts a bundle of parallel rays
  to make an angle a, with the optical axis to a
  second parallel bundle with angle ß.
• The ratio ß/a is called the angular
  magnification. It equals the ratio between the
  retinal image sizes obtained with and without the
  telescope

10
(No Transcript)
11
Microscope

• A microscope is an instrument used to see objects
  too small for the naked eye.
• There are many types of microscopes, the most
  common and first to be invented is the optical
  microscope which uses light to image the sample.

12
Microscope

• The objective lens is a magnifying glass with a
  short focal length.
• When the sample is brought close to the objective
  lens, a magnified, virtual image is obtained.
• The ability of a microscope to enlarge the
  resolve the image is through varying the focal
  length.

13
(No Transcript)
14
Magnifying glass

• A magnifying glass is a convex lens which is used
  to produce a magnified image of an object.
• It creates a magnified virtual image of an object
  behind the lens.
• The distance between the lens and the object must
  be shorter than the focal length of the lens.
• Otherwise, the image appears smaller and inverted.

15
(No Transcript)
16
Camera

• A camera is a device that records/stores images.
  These images may be still photographs or moving
  images such as videos or movies.
• Cameras may work with the light of the visible
  spectrum or with other portions of the
  electromagnetic spectrum.
• It generally consists of an enclosed hollow with
  an opening at one end for light to enter, and a
  recording or viewing surface for capturing the
  light at the other end.

17
Formation of a real image
18
Linear magnification
19
Focusing a camera
20
Camera aperture
21
Changing the aperture