A lens acts as converging in air and diverging when immersed in water. Then, refractive index of lens is :

• equal to unity

• below 1.33

• greater than 1.33

• less than unity

The angular resolution of a 10 cm diameter telescope at a wavelength of 5000 A is of the order of

• 10⁶ rad

• 10^-2 rad

• 10^-4 rad

• 10^-6 rad

The frequency of a light wave in a material is 2 x 10¹⁴ Hz and wavelength is 5000 A^o.  The refractive index of material will be

• 1.40

• 1.50 

• 3.00

• 1.33

The refractive index of glass is 1.520 for red light and 1.525 for blue light. Let D₁ and D₂ be angles of minimum deviation for red and blue light respectively in a prism of this glass. then,

• D₁ < D₂

• D₁ = D₂

• D₁ can be less than or greater than D₂ depending upon the angle of prism

• D₁ > D₂

In a laboratory four convex lenses L₁ ,L₂ , L₃ and L₄ of focal lengths 2, 4, 6 and 8 cm,respectively are available. Two of these lenses form a telescope of length 10 cm and magnifying power 4. The objective and eye lenses are respectively

• L₂ , L₃

• L₁, L₄

• L₁ , L₂

• L₄ , L₁

A symmetric double convex lens is cut in two equal parts by a plane perpendicular to the principal axis. If the power of the original lens is 4D, the power of a cut lens will be

• 2D

• 3D

• 4D

• 5D

In refraction, light waves are bent on passing from one medium to the second medium, because, in the second medium

•  the frequency is different

• the coefficient of elasticity is different

• the speed is different

• the amplitude is smaller

228.

A telescope has focal length of objective and eye-piece as 200 cm and 5 cm respectively. What is magnification of telescope?

• 40

• 80

• 50

• 0.01

Which of the following is true for rays coming from infinity?

• Two images are formed

• continuous image is formed between focal points of upper and lower lens

• One image is formed

• None of the above

A plane mirror produces a magnification of

• zero

• -1

• +1

• between 0 and +1