Using Huygens' principle, establish the law of reflection.

Let X Y be a plane reflecting surface and A B be a plane wavefront incident on the surface as shown in the figure. According to Huygens' principle, every point on the wavefront A B is a source of secondary wavelets, and the during which the wavelet from B to C reaches, the reflected wavelet from A would arrive at D . t = B C v = A D v or B C = A D ⋯ ( i ) Where v is the velocity in the medium. In right triangle ∠ ∆ A B C , sin i = B C A C B C = A C sin i ⋯ ( ii ) In right triangle ∠ ∆ A D C , sin r = A D A C A D = A C sin r ⋯ ( iii ) Putting equations (ii) and (iii) in equation (i) A C sin i = A C sin r sin i = sin r ⇒ i = r i.e Angle of incidence = angle of refraction This is the first law of reflection. From the figure, the incident ray, the reflected ray, and the normal all lie on the same plane X Y . This proves the second law.

E M B I B E

Physics Standard 12>Chapter 7 - Wave Optics>Exercises>Q 20

MEDIUM

12th Maharashtra Board

IMPORTANT

Earn 100

The intensity of the light coming from one of the slits in Young's experiment is twice the intensity of the light coming from the other slit. What will be the approximate ratio of the intensities of the bright and dark fringes in the resulting interference pattern?

Important Questions on Wave Optics

HARD

12th Maharashtra Board

IMPORTANT

Physics Standard 12>Chapter 7 - Wave Optics>Exercises>Q 21

A parallel beam of green light of wavelength

550 nm

passes through a slit of width

0.4 mm

. The intensity pattern of the transmitted light is seen on a screen which is

40 cm

away. What is the distance between the two first order minima?

HARD

12th Maharashtra Board

IMPORTANT

Physics Standard 12>Chapter 7 - Wave Optics>Exercises>Q 22

What must be the ratio of the slit width to the wavelength for a single slit to have the first diffraction minimum at 45.0°?

HARD

12th Maharashtra Board

IMPORTANT

Physics Standard 12>Chapter 7 - Wave Optics>Exercises>Q 23

Monochromatic electromagnetic radiation from a distant source passes through a slit. The diffraction pattern is observed on a screen $2.50 m$ from the slit. If the width of the central maximum is $6.00 mm$ , what is the slit width if the wavelength is $500 nm$ (visible light);

HARD

12th Maharashtra Board

IMPORTANT

Physics Standard 12>Chapter 7 - Wave Optics>Exercises>Q 23

Monochromatic electromagnetic radiation from a distant source passes through a slit. The diffraction pattern is observed on a screen $2.50 m$ from the slit. If the width of the central maximum is $6.00 mm$ , what is the slit width if the wavelength is $50 μ m$ (infrared radiation);

HARD

12th Maharashtra Board

IMPORTANT

Physics Standard 12>Chapter 7 - Wave Optics>Exercises>Q 23

Monochromatic electromagnetic radiation from a distant source passes through a slit. The diffraction pattern is observed on a screen $2.50 m$ from the slit. If the width of the central maximum is $6.00 mm$ , what is the slit width if the wavelength is $0.500 nm$ (X-rays)?