Electricity — Science STD 10 — Question

At what distance should an object be placed from a convex lens of focal length 18cm to obtain an image at 24cm from it on the other side? What will be the magnification produced in this case?

Of the three metals X, Y and Z. X reacts with cold water, Y with hot water and Z with steam only. Identify X, Y and Z and also arrange them in order of increasing reactivity.

Explain how tidal energy can be used to generate electricity.

Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W . How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A ?

What can you see in a completely dark room? If you switch on an electric bulb in this dark room as a light source, explain how you could now see:

1. The electric bulb.
2. A piece of white paper.

What is an ecosystem? List its two main components. We do not clean natural ponds or lakes but an aquarium needs to be cleaned regularly. Why is it so? Explain.

Name the water and minerals conducting element of non-flowering plants. Mention how conduction takes place in it.

The radius of curvature of a concave mirror is 50cm. Where should an object be placed in the mirror, so as to form its image at infinity? Justify your answer.

P, Q, R and S are four major types of phytohormones. P is a phytohormone which functions mainly as a growth inhibitor. It promotes the wilting and falling of leaves. Q, R and S are phytohormones which all promote growth of plants in various ways. Q is responsible for the phenomenon of phototropism in plants. R is involved mainly in shoot extensions. The phytohormone S helps in breaking the dormancy of seeds and buds. What are P, Q, R and S? Give one reason each for your choice.

Give reasons:
Baking powder is added to make the cakes spongy and soft.