A concave mirror and a converging lens (glass with $\mathrm{\mu } = 1.5$) both have a focal length of 3 cm when in air. When they are in the water $\left(\mathrm{\mu } = \frac{4}{3}\right)$, their new focal length are:

1.  ${\mathrm{f}}_{\mathrm{Lens}} = 12 \mathrm{cm}, {\mathrm{f}}_{\mathrm{Mirror}} = 12 \mathrm{cm}$

2.  ${\mathrm{f}}_{\mathrm{Lens}} = 3 \mathrm{cm}, {\mathrm{f}}_{\mathrm{Mirror}} = 12 \mathrm{cm}$

3.  ${\mathrm{f}}_{\mathrm{Lens}} = 3 \mathrm{cm}, {\mathrm{f}}_{\mathrm{Mirror}} = 3 \mathrm{cm}$

4.  ${\mathrm{f}}_{\mathrm{Lens}} = 12 \mathrm{cm}, {\mathrm{f}}_{\mathrm{Mirror}} = 3 \mathrm{cm}$

A soldier directs a laser beam on an enemy by reflecting the beam from a mirror. If the mirror is rotated by an angle $\mathrm{\theta }$, by what angle will be reflected beam rotate?

1.  $\mathrm{\theta }$/2

2.  $\mathrm{\theta }$

3.  2$\mathrm{\theta }$

4.  None of these

When an object is at a distance of ${\mathrm{\mu }}_1 \mathrm{and} {\mathrm{\mu }}_2$ from the poles of a concave mirror, images of the same size are formed. The focal length of the mirror is:

1.  ${\mu }_1 + {\mu }_2$

2.  ${\mu }_1 - {\mu }_2$

3.  $\frac{{\mu }_1 + {\mu }_2}{2}$
4.  $\frac{{\mu }_1 - {\mu }_2}{2}$

A given ray of light suffers minimum deviation in an equilateral prism P. Additional prism Q and R of identical shape and of the same material as P is now added as shown in the figure. The ray will now suffer:

1.  greater deviations 

2.  no deviation

3.  same deviation as before 

4.  total internal reflection

For a spherical mirror, the graph of 1/v versus 1/u is given by:

1.  

2.  

3.  

4.  

The focal length of the objective and the eyepiece of a microscope are 4 mm and 25 mm respectively. If the final image is formed at infinity and the length of the tube is 16 cm, then the magnifying power of the microscope will be:

1.  -327.5

2.  -3.75

3.  3.3275

4.  32.75

The figure shows a concavo-convex lens. What is the condition on the refractive indices so that the lens is diverging?

1. $2{\mu }_3<{\mu }_1+{\mu }_2$

2. $2{\mu }_3>{\mu }_1+{\mu }_2$

3. ${\mu }_3>2({\mu }_1-{\mu }_2)$

4. None of these

Statement I: If a source of light is placed in front of the rough wall its image is not seen.

Statement II: The wall does not reflect light.

1. Statement I is true, statement 2 is true; statement 2 is the correct explanation for statement I

2. Statement 1 is true, statement 2 is true; statement 2 is not the correct explanation for statement 1

3. Statement 1 is true, statement 2 is false.

4. Statement 1 is false, statement 2 is true

A thin prism having refracting angle 10⁰ is made of glass of refractive index 1.42. This prism is combined with another thin prism of a glass of refractive index 1.7. This combination produces dispersion without deviation. The refracting angle of the second prism should be:-

1. $6^o$

2. $8^o$

3. ${10}^o$

4. $4^o$

In an astronomical telescope in normal adjustment, a straight line of length L is drawn on inside part of the objective lens. The eye-piece forms a real image of this line. The length of this image is I. The magnification of the telescope is :

1. $\frac{L}{I}+1$

2. $\frac{L}{I}-1$

3. $\frac{L+1}{I-1}$

4. $\frac{L}{I}$