How do Organisms Reproduce? — Science STD 10 — Question

The shiny outer surface of a hollow sphere of aluminium of radius 50cm is to be used as a mirror:

1. What will be the focal length of this mirror?
2. Which type of spherical mirror will it provide?
3. State whether this spherical mirror will diverge or converge light rays.

Giving reasons, state the ‘signs’ (positive or negative) which can be given to the following:

1. Object distance (u) for a concave mirror or convex mirror.
2. Image distances (v) for a concave mirror.
3. Image distances (v) for a convex mirror.

Any four methods of contraception used by humans. How does their use have a direct effect on the health and prosperity of the family?

How does inserting the control rods in the graphite core affect the fission in the reactor? Explain your answer.

How do organisms, whether reproduced asexually or sexually maintain a constant chromosome number through several generations? Explain with the help of suitable example.

With the help of a flow chart explain in brief how the sex of a newborn is genetically determined in human beings. Which of the two parents, the mother or the father, is responsible for determination of the sex of a child?

The atomic masses of three elements X, Y and Z having similar chemical properties are 7, 23 and 39 respectively.

1. Calculate the average atomic mass of elements X and Z.
2. How does the average atomic mass of elements X and Z compare with the atomic mass of element Y?
3. Which law of classification of elements is illustrated by this example?
4. What could the elements X, Y and Z be?
5. Give another example of a set of elements which can be classified according to this law.

Derive the expression for the heat produced due to a current ‘I’ flowing for a time interval ‘t’ through a resistor ‘R’ having a potential difference ‘V’ across its ends. With which name is this relation known?