Rohan conducted experiments on echo in different media. He observed that a minimum distance of ‘x’ meters is required for the echo to be heard in oxygen and ‘y’ meters in benzene. Compare ‘x’ and ‘y’. Justify your answer.

Speed of sound in oxygen: 340 ms^-1

Speed of sound in benzene: 200 ms^-1

(a) In a reading glass what is the position of the object with respect to the convex lens used?

(b) Why can we not use concave lens for the same purpose?

State two factors affecting the speed of rotation of the coil in a D.C. motor.

How much heat is required to convert 500 g of ice at 0°C to water at 0°C? The latent heat of fusion of ice is 330 J g⁻¹.