Acids, Bases and Salts — Science STD 10 — Question

How is ozone formed in the upper atmosphere? Why is damage to ozone layer a cause of concern to us? What causes this damage?

List three techniques that have been developed to prevent pregnancy. Which one of these techniques is not meant for males? How does the use of these techniques have a direct impact on the health and prosperity of a family?

An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.

Name two metals which react violently with cold water. Write any three observations you would make when such a metal is dropped into water. How would you identify the gas evolved, if any, during the reaction?

Why do elements in the same group show similar properties but the elements in different groups show different properties?

Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.

List three factors that provide evidences in favour of evolution in organisms and state the role of each in brief.

A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases?

A lens of focal length 20cm is used to produce a ten times magnified image of a film slide on a screen. How far must the slide be placed from the lens ?

What is a ‘food web’? Show its formation.