A star emitting light of wavelength 5896 Å is moving away from the earth with a speed of 3600 km/sec. The wavelength of light observed on earth will

(1) Decrease by 5825.25 Å

(2) Increase by 5966.75 Å

(3) Decrease by 70.75 Å

(4) Increase by 70.75 Å

(c = 3 × 108 m/sec is the speed of light)

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A heavenly body is receding away from the earth such that the fractional change in λ is 1, then its velocity is :

(1) C

(2) $\frac{3C}{5}$

(3) $\frac{C}{5}$

(4) $\frac{2C}{5}$

Concept Questions :-

Wave front
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A slit of width a is illuminated by white light. For red light (λ = 6500 Å), the first minima is obtained at θ = 30°. Then the value of a will be

(1) 3250 Å

(2) 6.5 × 10–4 mm

(3) 1.24 microns

(4) 2.6 × 10–4 cm

Concept Questions :-

Diffraction
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The radius of central zone of the circular zone plate is 2.3 mm. The wavelength of incident light is $5893\text{\hspace{0.17em}\hspace{0.17em}}Å.$ Source is at a distance of 6m. Then the distance of the first image will be

(1) 9 m

(2) 12 m

(3) 24 m

(4) 36 m

Concept Questions :-

Huygens' principle
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What will be the angular width of central maxima in Fraunhoffer diffraction when light of wavelength $6000\text{\hspace{0.17em}}Å$ is used and slit width is 12×10–5 cm

Concept Questions :-

Diffraction
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Direction of the first secondary maximum in the Fraunhofer diffraction pattern at a single slit is given by (a is the width of the slit)

(1) $a\mathrm{sin}\theta =\frac{\lambda }{2}$

(2) $a\mathrm{cos}\theta =\frac{3\lambda }{2}$

(3) $a\mathrm{sin}\theta =\lambda$

(4) $a\mathrm{sin}\theta =\frac{3\lambda }{2}$

Concept Questions :-

Diffraction
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A parallel monochromatic beam of light is incident normally on a narrow slit. A diffraction pattern is formed on a screen placed perpendicular to the direction of the incident beam. At the first maximum of the diffraction pattern, the phase difference between the rays coming from the edges of the slit is

(1) $0$

(2) $\frac{\pi }{2}$

(3) $\pi$

(4) 2$\pi$

Concept Questions :-

Diffraction
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A parallel beam of monochromatic light of wavelength 5000 Å is incident normally on a single narrow slit of width 0.001 mm. The light is focused by a convex lens on a screen placed on the focal plane. The first minimum will be formed for the angle of diffraction equal to

(1) 0o

(2) 15o

(3) 30o

(4) 60o

Concept Questions :-

Diffraction
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In the far field diffraction pattern of a single slit under polychromatic illumination, the first minimum with the wavelength ${\lambda }_{1}$ is found to be coincident with the third maximum at ${\lambda }_{2}$. So

(1) $3{\lambda }_{1}=0.3{\lambda }_{2}$

(2) $3{\lambda }_{1}={\lambda }_{2}$

(3) ${\lambda }_{1}=3.5{\lambda }_{2}$

(4) $0.3{\lambda }_{1}=3{\lambda }_{2}$

Concept Questions :-

Diffraction
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The angle of polarisation for any medium is 60o, what will be critical angle for this

(1) ${\mathrm{sin}}^{-1}\sqrt{3}$

(2) ${\mathrm{tan}}^{-1}\sqrt{3}$

(3) ${\mathrm{cos}}^{-1}\sqrt{3}$

(4) ${\mathrm{sin}}^{-1}\frac{1}{\sqrt{3}}$

Concept Questions :-

Polarization of light