A concave mirror gives an image three times as large as the object placed at a distance of \(20~\text{cm}\) from it. For the image to be real, the focal length should be:

1.	\(10~\text{cm}\)	2.	\(15~\text{cm}\)
3.	\(20~\text{cm}\)	4.	\(30~\text{cm}\)

If the focal length of the objective lens is increased, then magnifying power of:

The correct mirror image of the figure is:
       

1.		2.
3.		4.

A mark on the surface of the sphere \(\left(\mu= \frac{3}{2}\right)\) is viewed from a diametrically opposite position. It appears to be at a distance \(15~\text{cm}\) from its actual position. The radius of the sphere is:
1. \(15~\text{cm}\)
2. \(5~\text{cm}\)
3. \(7.5~\text{cm}\) 
4. \(2.5~\text{cm}\)

A concave lens of focal length \(25~\text{cm}\) produces an image \(\frac{1}{10}\text{th}\)$$ of the size of the object. The distance of the object from the lens is:

The focal lengths of the objective and eyepiece of a compound microscope are \(2​​\text{cm}\) and \(6.25​​\text{cm}\) respectively. An object \(AB\) is placed at a distance of \(2.5​​\text{cm}\) from the objective which forms the image \(A'B'\) as shown in the figure. The maximum magnifying power in this case, will be:
          

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

In the diagram shown below, the image of the point object \(O\) is formed at \(l\) by the convex lens of focal length \(20~\text{cm},\)  where \(F_1\) and \(F_2\) are foci of the lens. The value of \(x'\) is:
        

In the following diagram, what is the distance \(x\) if the radius of curvature is \(R= 15​​\text{cm}?\)