Question

Rajesh is a student of class X and his brother Ram is studying in

class VII. Rajesh told Ram that he would show a magic to him.

Rajesh had a lens. He focussed the sun rays on the dry leaves in

their garden. After sometime the leaves were burnt​

Answer 1

Answer:

convex lens

Explanation:

convex lens are converging lens since they converge sunlight and form heat energy to burn the leaf

Answer 2

Correct Question:

Rajesh is a student of class X and his brother Ram is studying in class VII. Rajesh told Ram that he would show a magic to him. Rajesh had a lens. He focussed the sun rays on the dry leaves in their garden. After sometime the leaves were burnt.

What lens did he use ? Justify .

Solution:

• Rajesh used a bi-convex lens to burn the leaves.

• Since the source of light (i.e. sun) is located far away from us, we can consider it to be situated at infinity.

• Now, paraxial light rays from the source after getting refracted from the convex lens converge at the focus.

• Rajesh kept the leaves in such a way that they were located at the position of the focus of the lens.

• At the focus, the light rays converged and concentrated a lot amount of energy.

• This resulted in excessive increase in temperature at that position. The temperature became greater than the ignition temperature of the leaves.

• This caused the leaves to get burnt.

$\star$ Hope It Helps.