Reena and Vani find a discarded plastic lens lying on the beach. The girls’ discuss what they learnt in Physics and argue whether the lens is a converging or diverging one. When they look through the lens, they notice that the objects are inverted.

i) If an object 25 cm in front of the lens forms an image 20 cm behind the lens, what is the focal length of the lens?

ii) Is it a converging or diverging lens?

Ranjini makes arrangements for a candle-light dinner and tops it with a dessert of elatine filled blue berries. If a blueberry that appears at an angle of 45^o to the normal in air is really located at 30^o to the normal in elatine, what is the index of refraction of the elatine?

If the far point of a myopic person is 75 cm, what should be the focal length of the lens used to rectify this defect?

Light which is incident on a flat surface makes an angle of 150 with the surface.

i) What is the angle of incidence?

ii) What is the angle of reflection?

iii) Find the angle of deviation.

How can you identify the three types of mirrors without touching them?

Give reasons.