If the space between two convex lenses of glass in the combination shown in the figure below is filled with water, then

1.  The focal length of the system will decrease

2.  The focal length of the system will increase

3.  Power of the system will increase

4.  Power of the system will become infinite  

A prism of refracting angle $30°$, has one of the refracting faces polished. A beam of light incident on the other refracting face with i = $60°$ will retrace its path, if the refractive index of prism would be

1.  $\sqrt{2}$

2.  $\sqrt{3}$

3.  $\sqrt{5}$

4.  $\sqrt{7}$

The Refractive index of material of an equilateral prism is $\sqrt{2}$. Angle of incidence for minimum deviation is:

1. \(60^{\circ}\)${}^{}$

2. \(45^{\circ}\)$$

3. \(30^{\circ}\)$$

4. \(15^{\circ}\)$$

To form an achromatic combination, two lenses of focal length X and Y and dispersive power A and B respectively, are kept in contact. Which of the following is correct?

1.  A = C, B = C/2; X = 2Y

2.  A = C, B = C/2; X = -2Y

3.  A = C, B = 2C; X = 2Y

4.  A = C, B = 2C; X = -2Y 

In a glass ($\mu =1.5$) sphere of radius 10 cm, there is an air bubble B at distance 5 cm from C. The distance of bubble from the surface of the sphere (i.e. point A) as observed from point P in the air will be

(1) 4.5 cm

(2) 20.0 cm

(3) 9.37 cm

(4) 6.67 cm

A concave lens is made of three layers of glass of three different materials as shown in the furure. A point object is placed on its axis. Number of images of the object is -

1. 2

2. 3

3. 4

4. 1

An object is placed at a distance of 20 cm from the thin lens as shown in the figure. The points $C_1$ and $C_2$ denote centres of curvature. The magnification produced by the lens is (Refractive index of glass is 1.5)

1.  -2

2.  +2

3.  -1/2

4.  +1/2

A lens forms image of a point object placed at distance 20 cm from it, just in front of the object at distance 4 cm from the object towards the lens. The power of lens is

(1) -2.25 D

(2) 1.75 D

(3) -1.25 D

(4) 1.4 D

A point object O is placed on the principal axis of the convex lens of focal length f = 20 cm at a distance of 40 cm. The diameter of the lens is 10 cm. An eye is placed 60 cm to the right of lens and a distance h below the principal axis. The maximum value of h to see the image is-

1. Zero 

2. 2.5cm

3. 5cm

4.10cm 

If the wavelength of a ray of light from a source of lights is 3000 $\stackrel{0}{A}$in air, then the wavelength of that ray of light in a liquid in which S is placed will be:

(1) 4000 $\stackrel{0}{A}$

(2) 1500 $\stackrel{0}{A}$

(3) 9000 $\stackrel{0}{A}$

(4) 3500 $\stackrel{0}{A}$