DC Circuit - Short Questions and Answers

DC Circuit - Short Questions and Answers Points : dc circuit short questions and answers Q. 1. Can you calculate the e.m.f of a cell by a voltmeter? Ans : Not precisely. It is because as voltmeter is linked across the cell current starts- flowing through it This causes a voltage drop across the inner resistance of cell. Thus the voltmeter will not specify the e.m.f. of the cell. Remember e.m.f. of a cell is the voltage across open-circuit terminals of the cell z e., voltage across the terminals of cell when it carry no current. Q. 2. What is objection to have lamps in a house-lighting circuit connect in series? Ans : The lamps in a house-lighting circuit are not connect in series due to following reasons:

(i) For capable operation, only those lamps or devices can be connected in series that to have the similar current score. Though, electrical devices (e.g., toaster, heater, lamp etc.) contain different current ratings. Clearly, they cannot be connect in series for capable operation.
(ii) A high supply voltage is necessary if lams (or other devices) are to be linked series. For example, if five 230 V lamps are to be connected in series, then supply voltage would contain to be 5 x 230 = 1150 V. Thus, series connection is not feasible for lighting circuits.
(iii) If break occurs in any part of circuit, no current will flow and the whole circuit becomes useless. Q. 3. It is general belief that a person touching a high power line gets stuck to the line is it true? Ans : This is not accurate. The reality is that a current of even a few mA is sufficient to make nervous system useless for a moment. As a result, the affect person has trouble to confiscate his hand off the live wire. We think that the person has got fixed to line. Q. 4. Why does the glow of lamps become weaker when a weighty current appliance is switched on in house? Ans : Domestic appliances are attached in parallel across the supply. While heavy current appliance is switched, total resistance of the system in room is decrease as, appliance is connected in parallel ‘by other loads. This increase the line current. This in turn causes better voltage drop in line. Thus, the voltage available crossways the lamps decreases and so is their glow. Q.5. Why is Wheatstone bridge method preferred to voltmeter-ammeter method for measuring resistance? Ans : Wheatstone bridge technique is preferred to voltmeter-ammeter technique, for measuring resistance due to following reasons:

(i) It eliminate objectionable element of voltmeter-ammeter technique where the precision of measurement is incomplete by the precision of calibration of instruments.
(ii) Wheatstone bridge technique is independent of fluctuations and variations in supply voltage. Q. 6. What is the meaning of algebraic sum? Ans : The aIgebraic sum is one in which sign of the amount is taken into account. For exemplar, if a current flowing towards a point 0 is assign ‘positive’ sign, then current flow away as of point 0 will be assign negative sign. Equally, if a rise in voltage is assign positive sign, then fall in voltage will be assign negative sign. Q. 7. Why are domestic appliances connected in parallel? Ans : Domestic appliances can connected in parallel suitable to following reasons:

(i) If break occurs in a few one of branch circuits, it will contain no effect on other branch circuits.
(ii) Domestic appliances are rate for similar voltage (that is, 230 V) but dissimilar powers. While connected in parallel, performance of every appliance becomes independent of other. Therefore a 230 V. 250W TV receiver can be operate separately in parallel by a 230 V, 100 W lamp. Q. 8. The resistance of human body is quite high (a few k ohm Why does one experience a strong shock as of 230 V supply ? Ans : The human body is extremely sensitive to even minute current. A current as low as a few mA can wholly affect nervous system. Q. 9. Which type of grouping of cells will lie suitable to obtain higher current and voltage? Ans : Series-parallel groping of cells; To create a large voltage, a number of cells are linked in series and to create a large current, a number of sets of such series-connected cells are connected in parallel. Such a connection is call series-parallel grouping. Q.10. Why does a cell possess internal resistance? Ans : While current flows through a cell, it meets resistance as of electrodes and the electrolyte. This resistance to current accessible through the cell is call its inside resistance. Q. 11. Why is Wheatstone circuit called a bridge? Ans : The circuit is call a bridge as the galvanometer bridges the opposite junctions of circuit. Q. 12. When we need a d.c. supply we take for a d.c. source other than a battery. Why? Ans : As batteries are costly and require frequent replacement Q. 13. A high voltage supply should have high internal resistance. Why ? Ans : If internal resistance of a high voltage supply is small, then on chance short-circuit, a damaging large current will flow through the source of em.f. This might damage high voltage source. For this cause, a high voltage supply must have high internal resistance.