Capacitance - Short Question and Answer

Capacitance - Short Question and Answer Points : capacitance - short question and answer Q. 1. Two spheres of different capacitances are electric to different potentials. They are then connected through a wire. Will total power increase, decrease or stay the same? Ans : The two spheres are at dissimilar potentials. Then, when they are attached through a wire, there will be redistribution of charge that is., flow of charge through wire) till the two spheres reach the similar potential. Due to flow of charge through connecting wire, A few energy will be lost as heat. Therefore, total energy after connecting the spheres will decrease. Q. 2. How does a spark discharge happen among two charged objects? Ans : Air among two charged objects is subjected to an electric field. If potential incline in intervening air column becomes high sufficient, air is ionised and conducting pathway is produced for free electrons which move crossways to discharge surfaces. Stored electric potential energy is dissolute as heat, light and sound. Q 3. Can there be potential dissimilarity between two adjacent conductors which carry the similar positive charge? Ans : Yes. We identify that V= q/C. The capacitance depends upon dimensions of conductor. If the two conductors are of dissimilar shapes and sizes, they will be charged to dissimilar potentials when given similar charge. Q. 4. A few conducting object attached to earth is said to be grounded. Clarify. Ans : Earth is an voting source or sink and is randomly said to be at zero potential. A conducting body attached to earth is also at zero potential or “ground potential”. Otherwise, capacitance of earth is so large that elimination of electrons as of it or supply of electrons to it makes no difference also in charge or potential of earth. Q. 5. What law is obey through a charging capacitor ? What is characteristic of such a laws? Ans : Charging of a capacitor obey exponential law. A amount is said to differ exponentially if it changes to half of its value in say x seconds and in next x seconds, value changes to half the new value and so on. Q. 6. If a solid dielectric is placed among the plates of a capacitor, its capacitance increases. Is there some additional advantage of solid dielectric? Ans : There are other two return of a solid dielectric. First, it helps in keeping plates close jointly without touching. Secondly, we preserve now charge capacitor to a higher potential (V=q/C). Q. 7. Two charged conductors are touch mutually and then divided. What will be the charge on them ? Ans : Charge on them will be separated in the ratio of their capacitances. We identify that q = CV. While charged conductots touch, they obtain the same potential. Hence, q x C. Q. 8. Given a solid metal sphere and a hollow metal sphere. Which will hold more charge? Together spheres are of similar radius. Ans : Both spheres will hold the similar charge: It is because charge remnants on outer surface of a charged conductor (whether solid or hollow) and the spheres have equivalent surface areas. Q. 9. Why do most changeable capacitors use air as the dielectric? Ans : Most variable capacitors have an air dielectric as of following reasons:
(i) The ‘all out’ (i.e.. minimum) capacitance is extremely low.
(ii) Air is the majority perfect dielectric material known.
(iii) There is minimum squander of energy and so efficiency is extremely high. Q. 10. What are differences among conductors and dielectrics? Ans : (i) There is no edge to current that a conductor can take, provide that it can be kept cool sufficient. Though, there is a limit to electric flux that a dielectric will take with no breaking down.
(ii) Conductors contain a large number of free electrons as dielectrics have practically no free electrons.
(iii) Dielectric power of conductors is zero as that of dielectrics is finite.
(iv) While a conductor is located in an exterior electric field, there is no electric field inside conductor. Though, as a dielectric is placed in an electric field, its molecules are polarised. The cause of this polarisation is to fail the applied electric field in the dielectric.
(v) Dielectric steady of conductors is infinity as chat of dielectrics is limited Q. 11. How is energy stored in a capacitor? Ans : Charging of a capacitor means transferring electrons as of one plate of capacitor to other. This involves expenses of energy because electrons have to be enthused against opposing forces. This energy is stored in the electrostatic field set up in dielectric medium. On discharging capacitor, field collapses and stored energy is free. Q. 12. How will you get a high dc. voltage for testing reason? Ans : While a high d.c. voltage source is necessary for testing, a regular technique is to charge a group of capacitors in parallel. They are then re-connected in sequence by a proper switching agreement, giving an accessible voltage which equals the practical voltage multiplied by number of charged capacitors. Therefore a million volts can be obtain through charging 20 capacitors in parallel to 50,000 volts and then connecting them in series. Q. 13. Where do we use variable air capacitor? Ans : Variable air capacitor is multiplate air capacitor whose capacitance can be different through changing plate area. It is frequently use to tune in” radio stations in radio receiver. Capacitance of such uneven capacitors is as of zero to about 4000 uF. Q. 14. Is the name condenser suitable for a capacitor? Ans : Name condenser is given to device suitable to verity that when pd. is applied crossways it. the electric lines of force are strong in small space among plates. In fact, a capacitor is a device use for ‘condensing’ or accumulates the charge on plates. Term condenser is confusing and, thus, the term capacitor is prefer. Q. 15. What is the significance of time constant of a circuit? Ans : Time steady of a circuit tells about charging and discharging rate of a circuit. The larger time constant, the longer charging and discharing method will take to reach the stable state value and vice-versa. For instance, if the time constant of a circuit is 1 second (i.e. RC =1 second), it means that time necessary for capacitor voltage ti’ rise 63.2% of its final stable state value is 1 second. It may be noted that capacitor is approximately fully charged (99.3 %) after rime equal to 5 time constants (i.e., 5 RC). Q. 16. What precautions should be taken as capacitors are connected in series? Ans : While capacitors are related in series, it is essential to keep in mind that voltage crosswise capacitors in series are not the similar except capacitances are equivalent. The better voltage will be across the slighter capacitance, which may result in its failure if capacitances vary extremely much. Q. 17. Can you connect a capacitor directly to a d.c. source Ans : No, because there is no resistance to limit current in circuit. An uncharged capacitor is equal to a short circuit so distant as d.c. voltage source is anxious. Thus except a resistor is connected in series by a capacitor, flow of charging current while a voltage source is first attached to it is imperfect through the small internal resistance of source. The surge of current that flows while no resistor is present can be great sufficient to damage the capacitor or supply or equally.