The Fundamental Unit of Life — Science STD 9 — Question

Why does an object float or sink when placed on the surface of water?

A student placed a gas jar containing air in the upside down position over a gas jar full of red-brown bromine vapours. He observed that the red brown colour spread upwards into the jar containing air. Based on this observation, the student concluded that it is only the bromine vapour which moves up and diffuses into air in the upper jar, the air from the upper jar does not move down by diffusion into the lower jar containing bromine vapours. Do you agree with this conclusion of the student? Give reason for your answer.

How does a proton differ from an electron?

Differentiate between fibers and sclereids.

Calculate the power of a pump which lifts 100kg of water to a water tank placed at a height of 20min 10s. (Take, g = 10ms^-2)

Classify the following as physical or chemical changes:

1. Formation of curd from milk.
2. Condensation of steam.
3. Growth of a plant.
4. Breaking of a glass tumbler.