Sound waves travel faster in water than in air. Imagine a plane sound wavefront incident at an angle $$\alpha$$ at the air-water interface; the refracted wavefront making an angle $$\beta$$ with the interface. Then,
 1 $$\alpha>\beta$$ 2 $$\beta>\alpha$$ 3 $$\alpha=\beta$$ 4 the relation between $$\alpha~\&~\beta$$ cannot be predicted.
Subtopic: Â Huygens' Principle |
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When light is refracted into a medium then,
 1 its wavelength and frequency both increase. 2 its wavelength increases but frequency remains unchanged. 3 its wavelength decreases but frequency remains unchanged. 4 its wavelength and frequency both decrease.

Subtopic: Â Huygens' Principle |
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The wavefronts of light coming from a distant source of unknown shape are nearly:
1. plane
2. elliptical
3. cylindrical
4. spherical

Subtopic: Â Huygens' Principle |
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For light diverging from a point source:

 (a) the wavefront is spherical. (b) the intensity decreases in proportion to the distance squared. (c) the wavefront is parabolic. (d) the intensity at the wavefront does not depend on the distance.
Choose the correct option:
 1 (a), (b) 2 (a), (c) 3 (b), (c) 4 (c), (d)
Subtopic: Â Huygens' Principle |
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Plane waves of light of wavelength $$\lambda$$ are incident onto a convex lens, and the beam is brought to a focus. A plane slab of thickness $$t$$ having refractive indices $$\mu_1,~\mu_2$$ in the upper and lower halves is placed parallel to the incoming wavefronts. The phase difference between the wavefronts at the focus, coming from the upper and lower halves of the slab is:

1.  $$\dfrac{2 \pi}{\lambda}\left[\left(\mu_{1}-1\right) t+\left(\mu_{2}-1\right) t\right]$$
2.  $$\dfrac{2 \pi}{\lambda}\left(\mu_{1}-\mu_{2}\right) t$$
3.  $$\dfrac{2 \pi}{\lambda}\left(\dfrac{t}{\mu_{1}}-\dfrac{t}{\mu_{2}}\right)$$
4.  $$\dfrac{2 \pi}{\lambda}\left(\dfrac{t}{\mu_{1}}+\dfrac{t}{\mu_{2}}\right)$$
Subtopic: Â Huygens' Principle |
From NCERT