Measurement of Time and Motion — Science STD 7 — Question

Why did we use metal wire for making the electric circuit? Can we not use some other material for the wires?

Explain with the help of an example that the states of rest and motion are relative terms.

Why should we not taste unknown substances during experiments?

A food stall owner was preparing dough for making bhaturas. He added a pinch of yeast and sugar to the dough and left it in a warm place. After few hours, the dough had risen. There was a sour smell too. Why was sugar added to the dough?

Most of the physical changes are reversible. Give some examples with reasons.

Boojho has seen in television programmes that whales and dolphins often come up to the water surface. They even release a fountain of water sometimes while moving upwards. Why do they do so?

Phosphorus is kept in water. Why?

Why should factory waste be treated before release?

A goat eats away all the leaves of a small plant (balsam). However, in a few days, new leaves could be seen sprouting in the plant again. How did the plant survive without leaves?

Boojho made light from a laser torch to fall on a prism. Will he be able to observe a band of seven colours? Explain with a reason.