Coal and Petroleum — Science STD 8 — Question

Explain the difference between pure air and polluted air.

Explain how the Moon’s phases affect its visibility and position in the sky.

What are the differences between a Wildlife Sanctuary and a National Park?

Farmers in a village reported a decline in soil health after years of using synthetic fertilisers. They noticed fewer earthworms and harder soil. Suggest two sustainable practices they could adopt and explain their benefits.

How is reproduction in Hydra different from that in Amoeba?

Explain, what happens when a beam of sunlight is passed through a glass prism.

Give two examples each for a solid, liquid and gaseous fuel along with some important uses.

In case of a fire, before the firemen use the water hoses to throw water to douse fire, they shut off the electricity supply for the area. Explain why this is done.

Activity: To make an electric pen.
Materials required: Potassium iodide salt, water, metal sheet, starch solution, paper napkin, copper wire, battery.
Procedure
1. Take potassium iodide salt solution in a beaker, battery and a metal sheet.
2. Connect the metal sheet to the negative terminal of the battery.
3. Add a few drops of starch solution to it
4. Soak a paper napkin in the potassium iodide solution and place it on the metal sheet.
5. Connect another wire to the positive terminal of the battery. Write with the positive terminal on the paper napkin.
Answers the following questions.
(i) Are you able to write?
(ii) Why is it possible?