1st Year Physics Chapter 9 Notes

• Important 1st year physics chapter 9 mcqs from Punjab Textbook.
• Wavefronts:  Light is a type of energy which produces sensation of vision. But how does this energy propagate? In 1678, Huygen's, an eminent Dutch scientist, proposed that light energy from a luminous source travels in space as waves. The experimental evidence in support of wave theory in Huygen's time was not convincing. However, Young's interference experiment performed for the first time in 1801 proved wave nature of light and thus established the Huygen's wave theory. In this chapter you will study the properties of light, associated with its wave nature. Consider a point source of light at S (Fig. 9.1 a). Waves emitted from this source will propagate outwards in all directions with speed c. After time t, they will reach the surface of an imaginary sphere with centre as S and radius as ct.Every point on the surface of this sphere will be set into vibration by the waves reaching there. As the distance of all these points from the source is the same, their state of vibration will be identical. In other words, all the points on the surface of the sphere will have the same phase such a surface on which all the points have the same phase of vibration is known as wavefront.
• Huygen's principle
• Interference of light waves
• Conditions for detectable interference
• Important 1st year physics chapter 9 solved exercise from Punjab Textbook.
• Young's double-slit experiment: Thus in case of a point source, the wavefront is spherical in shape. A line normal to the wavefront, showing the direction of propagation of light is called a ray of light. With time, the wave moves farther giving rise to new wave- fronts. All these wavefronts will be concentric spheres of increasing radil as shown in Fig. 9.1 (a). Thus the wave propagates in space by the motion of the wavefronts. The distance between the consecutive wavefronts is one wave- length. It can be seen that as we move away at greater distance from the source, the wavefronts are parts of spheres of very large radii. A limited region taken on such a wavefront can be regarded as a plane wavefront (Fig.9.1b). For example, light from the Sun reaches the Earth with plane wavefronts. In the study of interference and diffraction, plane waves and plane wavefronts are considered. A usual way to obtain a Interference in thin films.
• Newton's rings
• Michelson interferometer
• Diffraction of light
• Diffraction due to a narrow slit
• Important 1st year physics chapter 9 long questions from Punjab Textbook.
• Diffraction grating: In the interference pattern obtained with Young's double slit experiment (Fig. 9.3 b), the central region of the fringe system is bright. If light travels in a straight line the central region should appear dark le.. the shadow of the screen between the two slits. Another simple experiment can be performed for exhibiting the same effect.
• Consider that a small and smooth steel ball of about 3 mm in diameter is illuminated by a point source of light. The shadow of the object is received on a screen as shown in Fig. 9.8. The shadow of the spherical object is not completely dark but has a bright spot at its centre. According to Huygen's principle, each point on the rim of the sphere behaves as a source of secondary wavelets which illuminate the central region of the shadow.
• Diffraction of X-rays by crystals
• Polarization
• Production and detection of plane-polarized light
• Important 1st year physics chapter 9 important long questions from Punjab Textbook.
• Optical rotation
• Important 1st year physics chapter 9 numericals from Punjab Textbook.