Science Que-Ans (Each of 2 Mark )

This can be established on the basis of Rutherford experiment. Since some alpha particles were repelled by the nucleus of the atom, it is expected to have the same charge as on alpha particles. Therefore, nucleus of an atom has positive charge.The nucleus of an atom contains two things: Protons and neutrons. Because neutrons have no charge and protons have positive charge, the overall charge of the nucleus is positive.

When the branch is, suddenly set in motion, the leaves attached to it tend to continue in their state of rest, on account of inertia of motion. Thus a lot of strain acts on the junction of the leaves and the branches. Due to this strain the weakly held leaves are left behind and, hence fall off the branch.

When the standing tanker suddenly picks up speed, the oil in it on account of inertia of rest tends to continue in its state of rest. Thus, in a way oil is left behind and, hence, exerts very large force on its rear wall. Conversely, when the moving tanker suddenly stops, the oil in it continues moving forward and, hence exerts a very large force on the front wall. These forces can crack the walls of the oil tanker. Therefore to avoid such a mis-hap, some space is left at the top of the tanker for the free movement of oil.

During summer, we perspire more because of the mechanism of our body which keeps us cool. When evaporation takes place then sweat particles gain energy from body surface and change into vapour. The heat energy equal to the latent heat of vaporisation is absorbed from the body leaving the body cool. Cotton, being a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation. On the other hand, synthetic clothes (made of nylon, polyester, etc.) do not absorb much of sweat and therefore, they cannot keep our body cool in summer.

Yes. Sound follows the same laws of reflection as light does. We can say that because here the directions in which the sound is incident and is reflected make equal angles with the normal to the reflecting surface at the point of incidence, and the three are in the same plane.

It all depends upon the amount of kinetic energy available with the constituent particles which determines their speed and the attractive forces existing between them.
1) If the constituent particles have sufficiently more kinetic energy, and they move so fast that they are not able to remain close to each other. Then the substance is in gaseous state.
2) If they are moving slowly enough then the force between the constituent particles have a chance to pull them together and the substance then exists in the form of a liquid.
3) If the constituent particles are moving so slowly that the forces of attraction hold them rigidly together, then substance exist in the form of a solid.
The important fact to keep in mind is that, 'the higher the temperature, the faster the constituent particles move'. Due to this reason, solids melt as the temperature increases and vapourises at yet higher temperatures. The exact temperature at which a change takes place depends on the strength of the force between the molecules.

All cutting instruments such as blades, axes etc. are sharpened so that the area of cross section decreases and hence exerted by them increases. Thus they can easily penetrate a given surface.

When salt is mixed with water it increases the density of water and, hence, its density becomes greater than that of the density of egg which now floats in it.