A double convex lens has two surfaces of equal radii \(R\) and refractive index \(m=1.5.\) We have:
1. \(f=R/2\)
2. \(f=R \)
3. \(f=-R\)
4. \(f=2R\)

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 was 4 D, the power of a cut-lens will be

1. 2 D

2. 3 D

3. 4 D

4. 5 D

A thin lens is made with a material having refractive index \(\mu=1.5\). Both sides are convex. It is dipped in water (\(\mu=1.33\)). It will behave like:
1. a convergent lens
2. a divergent lens
3. a rectangular slab
4. a prism

A convex lens is made of a material having refractive index \(1.2.\) Both the surfaces of the lens are convex. If it is dipped into water (\(\mu=1.33\) ), it will behave like:
1. a convergent lens
2. a divergent lens
3. a rectangular slab
4. a prism