Ray Optics and Optical Instruments Test - 2

Light from each point on a luminous object travels outward in all directions in straight lines. Light travels at very high speeds, but is not instantaneously everywhere. Light from a point object travels indefinitely until it collides with matter in its path to be partially absorbed and reflected.

In a convex lens,  (1/v)−(1/u)=(1/f)​
Or (1/v)​−(1/f)​=(1/u)​where u is always negative and f is always positive.
(1/v)​=(1/f)​−(1/u)​
So, as u is increased 1/u will decrease and  (1/f)​−(1/u)​ will increase, so, 1/v ​increases or v decreases.
So, its graph will be a hyperbola

P=P1 ​+P2 ​=+2 −1=+1 dioptre, lens behaves as convergent
F=1 ​/P=1/1 ​=1m=100cm

In air, all the colours of light travel with the same velocity with the same velocity, but in glass, velocities of different colours are different. Velocity of red colour is largest and velocity of violet colour is smallest. Therefore, after travelling through the glass slab, red colour will emerge first.

When the deviation is minimum, then the incidence angle and emergence angle are equal and this is possible only when the refracted ray inside the prism is parallel to the base of the prism. 
Minimum deviation is given by δ=2i −A, where A is prism angle.

Magnification of a telescope is given by:
M= θ_i /θ_o ​​​
10= (h/d_i )/(h/d_o ​) ​​
10= d_o ​​/d_{i ​}
Distance of image, d_{i ​} =d_o ​​/10

Magnifying power of a compound- microscope is given by m=−(l ​D ​/f₀ ​f_e ​)
where, l is length of tube
D is least distance of clear vision
f₀ ​is focal length of objective
f_e ​is focal length of eyepiece
So, clearly, it can be seen that focal length of objective and eyepiece needs to be decreased so that magnifying power increases.
 

The molecules of air and other fine particles in the atmosphere have a size smaller than the wavelength of visible light. These particles are more effective in scattering light of a shorter wavelength at the blue end than the light of the longer wavelengths at the red end. The red light has a wavelength 1.8  times greater than blue light. Thus, when sunlight passes through the atmosphere, the fine particles in the air scatter the blue color more strongly than red color. The scattered blue light enters our eyes and we see the blue color of the clear sky.