The focal length of a glass $\left(\mu =1.5\right)$ lens in air is 20 cm. If it is dipped in water $\left(\mu =\frac{4}{3}\right)$, its focal length in water will be:

1.	80 cm	2.	40 cm
3.	60 cm	4.	20 cm

When a concave mirror of focal length f is immersed in water, its focal length becomes f', then:

Two convex lenses of focal length X and Y are placed parallel to each other. An object at infinity from the first lens forms its image at infinity from the second lens. The separation between the two lenses should be:

A plane mirror is placed at the bottom of a fish tank filled with water of refractive index $\frac{4}{3}$. The fish is at a height 10 cm above the plane mirror. An observer O is vertically above the fish outside water. The apparent distance between the fish and its image is:
                         

1. 15 cm

2. 30 cm

3. 35 cm

4. 45 cm

If \(C_1,~C_2 ~\mathrm{and}~C_3\) are the critical angle of glass-air interface for red, violet and yellow color, then:

An object is placed 20 cm in front of a concave mirror of a radius of curvature 10 cm. The position of the image from the pole of the mirror is:

1. 7.67 cm

2. 6.67 cm

3. 8.67 cm

4. 9.67 cm

When a ray of light falls on a given plate at an angle of incidence \(60^{\circ}\), the reflected and refracted rays are found to be normal to each other. The refractive index of the material of the plate is:

A thin rod of length \(\frac{f}{3}\) lies along the axis of a concave mirror of focal length \(f\). One end of its magnified, real image touches an end of the rod. The length of the image is:

1. \(f\)

2. \(\frac{f}{2}\)$$

3. \(2f\)

4. \(\frac{f}{4}\)$$

A thin equiconvex lens of power P is cut into three parts A, B, and C as shown in the figure. If P₁, P₂, and P₃ are powers of the three parts respectively, then:

A medium shows relation between i and r as shown. If the speed of light in the medium is nc then the value of n is:

1. 1.5

2. 2

3. 2^–1

4. 3^–1/2