An electric switch is a device used to complete or break an electric circuit. Usually, it is manually operated.
Purpose of using electric switch: In 'ON' position, the switch allows the current to flow through the circuit. Thus, the circuit becomes a closed circuit. In 'OFF' position, the switch does not allow current to flow through the circuit. Thus, the circuit becomes an open circuit.
Examples: Electrical appliances such as fans, electric lamps, washing machines, juicer and mixer, TV radio, etc, have switches.

Elastic tapes are stretchable due to which their length can be increased during the measurement if it is not handle with care. Therefore, the measurement done by elastic tapes may be greater than the actual length of the object. So, we can say that elastic tapes are not accurate to measure a length.

The shadow of an aeroplane flying high in the sky is not seen on the ground because the ground will not act as screen for the aeroplane due to its high distance from the ground.

The habitats can be classified as:
Terrestrial habitats - Grassland and rice field
Aquatic habitats - Pond and ocean

The name of an object which does not allow the light to pass through it is an opaque object, e.g. wood.

The cells used in calculators are known as button cells, as they resemble the shape of a button. The plates of these cells are made from compounds of nickel and cadmium. The main advantage of these cells is that they can stay in an active stage for months without any leakage.

Fish breathes through gills which take up dissolved oxygen present in water. When it is kept out of the water, it is unable to respire due to difference in pressure of gas. Hence, it dies.

The light always travels in a straight line. This can be shown by performing a simple activity. For this, first of all let us take three cardboards of equal size. Now, a hole is made'at the centre of each cardboard at the same level. The three cardboard are placed on a flat table and aligned linearly as shown in the figure.
A candle is lighted at one end of the table with its flame at the level of the holes and is seen at the other end. It is observed that the light of the candle is seen effortlessly. Now, the middle one of the three cardboards is displaced from its position. Now, we are unable to see the light. The reason behind this is that the light travelling in the straight line is obstructed due the misalignment of the cardboards. This proves that light always travels in a straight line

(a) Land-motorcycle, car.
(b) Water-Boat, steamer.
(c) Air-Aeroplane, helicopter.