Answer briefly :
(a) How do you perceive the colour of an object ?
(b) Which part of our body helps us in maintaining the body balance ?
(c) How does the eye regulate the amount of light that falls on the retina.

How does Balanced diet help in our body?

Answer briefly: (a) Why are villi present in the intestine and not in the stomach? (b) How does pepsinogen change into its active form? (c) What are the basic layers of the wall of alimentary canal? (d) How does bile help in the digestion of fats?

Raju got an injury on the head during motorbike accident on the road. Later he faced a problem in maintaining balance of the body while walking or sitting. Which part of the brain do you think is affected?

Answer the following questions regarding earth's magnetism. a. A vector needs three quantities conventionally used to specify the earth's magnetic field. b. The angle of dip at a location in southern India is about 18^@ . Would you expect a greater or smaller dip angle in Britain ? c. If you made a map of magnetic field lines at Melboune in Australia, would the lines seem to go into the groung or come out of the ground ? d. In which direction would a compass free to move in the vertical plane point to , if located right on the geomagnetic north or south pole ? e. the earth' s field, it is claimed roughly approximates the field due to a dipole of magnetic moment 8 xx10^(22)JT^(-1) located at its centre. Check the order of magnitude of this number in some way. f. Geologists claim that besides the main magnetic N - S poles, there are several local poles on the earth's surface oriented in different directions. How is such a thing possible at all ?

a. What happens if a bar magnet is cut into two pieces : (i) transverse to its length , (ii) along its length ? b. A magnetised needle in a uniform magnetic field experiences a torque but no net force . An iron nail near a bar magnet , however , experiences a force of attraction in addition to a torque . Why ? c. Must every magnetic configuration have a north pole and a south pole ? What about the field due to a toroid ? d. Two identical looking iron bars A and B are given , one of which is definitely known to be magnetised. (We do not know which one ) . How would one ascertain whether or not both are magnetised ? If only one is magnetised , how does one ascertain which one ? [Use nothing else but the bars A and B ]

Answer the following questions . a. The earth's magnetic field varies from point is space. Does it also change with time ? It so , on what time scate does it change appreciably ? b. The earth's core is known to contain iron. Yet geologists do not regard this as a source of the earth's magnetism why ? c. The charged currents in the outer conducting regions of the earth's core are thought to be responsible for earth's magnetism . What might be the ' battery ' (i.e., the source of energy) to sustain these currents ? d. The earth may have even reversed the direction of its field several times during its history of 4 to 5 billion years. How can geologists know about the earth's field in such distant past ? e. The earth's field departs from its dipole substantially at large distances (greater than about 30,000 km) what agencies may be responsible for this distortion ? f. Interstellar space has an extremely weak magnetic field of the order of 10^(-12) T, Can such a weak field be of any significant consequence ? Explain. [Note : Exercise 2 is meant mainly to arouse your curiosity . Answers to some question above are tentative or unknown . Brief answers wherever possible are given at the end . For details , you should consult a good text on geomagnetism.]