a. A comb run through one's dry hair attracts small bits of paper. Why? What happens if the hair is wet or if it is a rainy day? (Remember, a paper doesn't conduct electricity.) b. Ordinary rubber is an insulator. But special rubber tyres of aircraft are made slightly conducting. Why is this necessary? c. Vehicles carrying inflammable materials usually have metallic ropes touching the ground during motion. Why? d. A bird perches on a bare high power line, and nothing happens to the bird. A man standing on the ground touches the same line and gets a fatal shock. Why?

Assertion : Vehicles containing inflammable materials usually have metallic ropes touching the ground during motion. Reason : Charge produced by friction causes fire so, metallic ropes touching the ground for discharging for the safety of vehicles.

Sperms have a tail, whereas eggs do not. Why so?

Explain i. Oxides of nitrogen have open chain structures while those of phosphorus have closed chain or cage structure. Why is it so? IIustrate with one structural example for each type of oxides or The oxides of phosphorus have cage strućtures but not open ones. ii. Elemental phosphorus does not exist as P_2 as N_2

Two wires A and B of the same material, having radii in the ratio 1:2 and carry currents in the ratio 4:1. The ratio of draft speed of electron in A and B is

During sunset , you might have noticed that the western horizon becomes reddish . Why is it so ?

In a nuclear reactor the chain reaction is carried out under controlled conditions. Name the material that is used as control rods in a nuclear reactor.

What happens to the oxygen ț{that reaches the lungs? } Haven't you leamt that respiration is' the exchange of gases? This gaseous exchange has three stages. We have so far discussed the first of these stages. Observe. the given illustration. How does the oxygen that enters the lungs reach the cells and the carbon dioxide formed in the cells reach the lungs? Haven'tyou understood from the illustration that it is the blood that carries oxygen to all cells and receives carbon.dioxide from the cells and carries it to the lungs? You have also learnt earitier that digested food components from the small intestine are carried to the cells by the blood..Isn't the human blood red in colour?

In $C_(4)$ plants, the leaves have a special type of anatomy to avoid photorespiration. a. What is the special anatomy called? Why is it so called? b. Give examples of two plants having this anatomy.

Immerse the plastic bottle to the bottom of the bucket. Don't you have to exert a force? Why is it so?