Questions and answers for AISSCE board exams

Question 1.  Why electron capture is common in case of heavy nucleus?
Answer. A heavy nucleus has large positive charge. Moreover, the raidus of K-shell in heavy nuclei is much smaller than that in case of light nucleus. Due to both these factors, the K-shell electrons experiences a large force of attraction due to positive nucleus and is keptured by it.

Question 2. Why is nuclear fusion difficult to carry out?
Answer. The fusion reaction require very high temperature condition and it has to be obtained by causing explosion due to fission process. Further , due to very high temperature no material can sustain the region where fusion is to be carried out.

Question 3. Would you prefer to use a transistor in CB or CE as a amplifier?
Answer. Transistor in CE configuration as an amplifier as curent gain in this case is more than that as in case of amplifier in CB configuration.

Question 4. Explain why the core of the transformer is laminated?
Answer. The core of a transformer is laminated so as to reduce loss of energy due to eddy currents. The magnitude of the eddy currents set up is considerably minimised, when the core is laminated.

Question 5. Why is the core of a transformer made of a magnetic material of high permeability?
Answer. The transformer works on the principle of mutual induction. In case, the core has a high value of magnetic permeability, the magnetic field lines will crowd through the core and the magnetic flux linkage between the two coils will also be large.

Question 6. When the motor of an electric refrigerator starts, the lights in the house become dim momentarily. Why?
Answer. When the electric motor of the refrigerator starts, it draws maximum current from the a.c. mains. It is because, just at the start of the motor, the back e.m.f. is zero. Due to the large current drawn by the motor, the current through the lights (connected in parallel) decreases and they become dim. However, as the armature of the motor rotates, back e.m.f. is produced and the motor draws current less than that drawn in the beginning . Then, the lights recover their brilliance.

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