Chapter slides of chapter 9 & 10 physics part 1

1. Physical optics
MUHAMMAD IMTIAZ
CS, YEAR 2
NAMAL COLLEGE, MIANWALI

2. Idea about physical optics
 Optics:
 A branch of physics in which we study all about light.
 physical optics:
 physical optics, or wave optics, is the branch of optics that studies interference,
diffraction, polarization and other phenomenon of light.

3. Some terminologies
 Wave front:
 A surface on which all points have same phase of vibration, known as wave front.
 Monochromatic light:
 A beam of light having same wavelength is called monochromatic light.
 Coherent sources:
 Monochromatic sources of light which emit waves having constant phase difference.

4. Huygens's principle
 Each point of wave front may be considered as a source of secondary wavelets
which spread out in forward direction with the speed equal to the speed of
propagation of waves.
 The new position of wave front can be founded by constructing a surface that
touches all the points.

5. Young’s double slit experiment
 If we placed a surface in front of light source it will behave a source of secondary
wavelets. When beams of light is emitted through those slits, they produces dark
and bright bands which can be seen on a screen placed parallel to the first screen.
 Maxima:
 The bright bands / fringes are called maxima.
 Minima:
 The dark bands are called minima.
Note: The central region of the fringes are bright.

6. Michelson’s interferometer
 Definition:
 It is an instrument devised by “Albert A. Michelson” in 1881 which is used to measure
distance with extremely high precision.
 He devised this instrument by using the idea of interference of light.
 For λ = 400nm, it measures up to precision of 400nm.

7. Diffraction of light
 Definition:
 The property of bending of light around the obstacles and spreading of light waves into
the geometrical shadows of obstacle is called Diffraction.
 This phenomena is found to be prominent if the wavelength of the light is greater than
the size of obstacle.
 This phenomena is occurs due to interference of light coming from different parts of the
same wave front.

8. Diffraction due to diffraction grating
 Diffraction grating:
 It is a glass plate having a large number of close parallel equidistant slits mechanically
ruled on it.
 A typical diffraction grating has about 400 to 5000 lines per centimeter.
 Grating element:
 The distance between two adjacent slits(d), called grating element.
 It is obtained by dividing the total length of grating to the total number of lines ruled on
it.

9. Optical instruments

10. Some terminologies
 Least distance:
 The minimum distance from the eye at which object appears distinct is called least
distance of distinct vision or near point.
 Magnification:
 The ratio of the size of the image to the size of the object, magnification.
 Angular magnification / magnifying power:
 It the ratio between the angle subtended by the image to the angle subtended by our
naked eye.

11. Continued…
 Resolving power:
 The ability of an instrument to reveal minor details of objects under examination.
 It is reciprocal of the minimum angle which two points subtends at the instruments.
 R = 1 /α 𝑚𝑖𝑛 = D / 1.22λ

12. Simple microscope
 Definition:
 An optical instrument which is used to see the minor details of the objects.
 It uses one convex lens.
 Magnification of simple microscope:
 M = 1 + d / f

13. Astronomical microscope
 Definition:
 An optical instrument which is used to see the distant objects.
 It uses two convex lenses.
 Magnification of astronomical microscope:
 M = focal length of the object / focal length of the eye piece

14. GKK / HKK
 Compound microscope
 Spectrometer
 Michelson’s method to measure speed of light
 Polarization from previous chapter

15. Optical fibers
 Intro:
 Communication of data(audio, video, telephone etc.) through light is done by fibers.
 Principle:
 Data is sent from one place to another place by total internal reflection and continuous
refraction.

16. Signal transmission and conversion to
sound
 An optic communication system consist of three major components:
 Transmitter that convert electrical signal to light signal.
 Optical fibers that guide the signals.
 Receiver that convert light signals to electrical signals.

17. Thank you