Life Processes — Science STD 10 — Question

A substance X which is used as an antacid reacts with dilute hydrochloric acid to produce a gas Y which is used in one type of fire-extinguisher. Name the substance X and gas Y. Write a balanced equation for the chemical reaction which takes place.

To find the image distance for varying object distances in case of a convex lens of focal length 15 cm, a student obtains on a screen a sharp image of a bright object by placing it at 20 cm distance from the lens. After that he gradually moves the object away from the lens and each time focuses the image on the screen.

1. In which direction-towards or away from the lens does he move the screen to focus the object?
2. How does the size of image change?
3. Approximately at what distance does he obtain the image of magnification -1?
4. How does the intensity of image change as the object moves farther and farther away from the lens?

It is desired to obtain an erect image of an object, using concave mirror of focal length of 12cm.
Will the image be smaller or larger than the object? Draw ray diagram to show the formation of image in this case.

Describe how hydro-energy can be converted into electrical energy. Write any two limitations of hydro-energy.

Name the source gland and one major effect of each of the following hormones:

1. Parathormone.
2. Progesterone.

How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?

A milkman adds a very small amount of baking soda to fresh milk.

1. Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
2. Why does this milk take a long time to set as curd?

Explain why, when the sun is overhead at noon, it appears white, but when the same sun is near the horizon at sunset, it appears red?

What is the difference between a real image and a virtual image? Give one example of each type of image.

What is puberty? Who attains puberty at an earlier age in human beings: male or female (boy or girl)?