Posts Tagged ‘Optics’

Huygens Wave Theory and rectilinear propagation of light

As per 12th Physics textbook, it has been mentioned that according to Huygens wave theory of light, light does not travel in straight line.

But I have heard that it is wrong and rectilinear propagation of light is one of the merits of Huygens theory rather than demerit please clear my doubt

Asked by Mohammed Faiz Ansari

Answer:

The wave nature of light becomes prominent only when the size of the aperture of the obstacle is comparable to the wavelength.

The light of wavelength λ coming through an aperture of width a can be considered to be in rectilinear motion up to a distance of

Z_F= a²/λ,

where Z_F is called the Fresnel distance.

As

Thus, wavelength λ decreases, the limit for rectilinear propagation increases.This is the reason why we say, ray optics is valid when the limiting case wavelength λ tending to zero is applied.

Numerical on Eye defect

A myopic eye has a far point of 3m and a near point of 150mm . State the type of spectacle lens needed for viewing an object at normal far point and determine its power in dioptres . Find the near point when wearing this lens ?

(Asked Zahraa via our mobile site http://m.askphysics.com)

Optics

Rajat asked:

“when we exchange the lenses of compound microscope, then why it does not act as a telescope?”

What accounts for the acceleration or deceleration of light when it travels from one medium to another?

“When light passes through different mediums speed changes but who provide acceleration to change velocity?”

This question was posted by Jishnu

Answer: Just imagine you are participating in a cross country race. When the road is good you can travel faster; but if the path is a marshy place, your speed will decrease. This is just an analogy. To understand it better, you should know that the way light travels in a medium is different from the way it travels in vacuum.