When a candle is lit the following are observed.
a. Wax melts.
b. Candle keeps burning
c. The size of the candle decreases.
d. The molten wax solidifies
e. Which of the changes can be reversed? Justify your answer.

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.]

During the stages of succession in a given ecosystem, the following changes in characteristics may be observed. Which one of the characteristics A,B,C,D or E is responsible for the apparent high degree of stability associated with a climax acosystem?

Answer the following questions, which help you to understand the difference between Thomson's model and Rutherford's model better. a. Is the average angle of deflection of a-particles by a thin gold foil predicted by Thomson's model much less, about the same, or much greater than that predicted by Rutherford's model? b. Is the probability of backward scattering (i.e., scattering of a-particles at angles greater than 90^@ ) predicted by Thomson's model much less, about the same, or much greater than that predicted by Rutherford's model? c. Keeping other factors fixed, it is found experimentally that for small thickness t, the number of alpha - particles scattered at moderate angles is proportional to t.What clue does this linear dependence on t provide? d. In which model is it completely wrong to ignore multiple scattering for the calculation of average angle of scattering of alpha particles by a thin foil?

State whether each of the following statement is true or false. Justify your answer. { a, e, i, o, u } and { a, b, c, d } are disjoint sets.

State whether the following statements are true or false? Also give reasons for your answers. a) Only one line can pass through a given point. b) All right angles are equal. c) Circles with same radii are equal. d) A line segment can be extended on its both sides endlessly to get a straight line. e) From the figure, AB gt AC .

Which two of the following changes (A-D) usually tend to occur in the plane dwellers when they move to high altitudes (3500 m or more)? A)Increase in red blood cell size B) Increase in red blood cell production c) Increased breathing rate d) Increase in thrombocyte count Changes occurring are:

Assertion (A) : Burning of a candle is considered a physical as well as chemical change. Reason (R) : Melting of wax is a physical change melted wax turns into vapours and then burns which is a chemical change.