What is capacitor ? And Questions Answer.

WHAT  IS  CAPACITOR   ?  Questions And Answer

   

A capacitor is a device that stores electrical energy in an electric field.

 It is a passive electronic component with two terminals. The effect of a capacitor is known as capacitance.

Capacitor is store Electrical charge.

Unit of capacitor is  farad.

Dielectric capacitor

Most capacitors have a dielectric spacer,  increases their capacitance compared to air or a vacuum. In order to maximise the charge that a capacitor can hold, the dielectric material needs to have as high a permittivity as possible, while also having as high a breakdown voltage as possible. The dielectric also needs to have as low a loss with frequency as possible.

 However, low value capacitors are available with a vacuum between their plates to allow extremely high voltage operation and low losses. Variable capacitors with their plates open to the atmosphere were commonly used in radio tuning circuits. Later designs use polymer foil dielectric between the moving and stationary plates, with no significant air space between the plates.

 Several solid dielectrics are available, including paper, plastic, glass, mica and ceramic

A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery, or like other types of rechargeable energy storage system.[70] Capacitors are commonly used in electronic devices to maintain power supply while batteries are being changed. (This prevents loss of information in volatile memory.)

 A capacitor can facilitate conversion of kinetic energy of charged particles into electric energy and store it.

 Conventional capacitors provide less than 360 joules per kilogram of specific energy, whereas a conventional alkaline battery has a density of 590 kJ/kg. There is an intermediate solution: Supercapacitors, which can accept and deliver charge much faster than batteries, and tolerate many more charge and discharge cycles than rechargeable batteries. They are, however, 10 times larger than conventional batteries for a given charge. On the other hand, it has been shown that the amount of charge stored in the dielectric layer of the thin film capacitor can be equal to, or can even exceed, the amount of charge stored on its plates.

Questions And Answer.

Q. 2. The plates of a charged capacitor are connected to a voltmeter. If the plates of the capaci- tor are separated further, what will be the effect on the reading of the voltmeter?

 Ans.    V = q/C    As the capacitor plates are separated, C decreases. Since charge on the plates remains the same, value of V increases. Hence, the reading of the voltmeter will increase. 

Q.   3. Any conducting object connected to earth is said to be grounded. Explain. 

Ans.    The earth is an electron source or sink and is arbitrarily said to be at zero potential. A conducting body connected to earth is also at zéro potential or "ground potential". Alternatively, the capacitance of earth is so large that removal of electrons from it or supply of electrons to it makes no difference either in the charge or potential of earth. 

Q.  4  How does a spark discharge occur between two charged objects?

 Ans.    The air between the two charged objects is subjected to an electric field. If the potential gradient in the intervening air column becomes high enough, the air is ionised and con- ducting path is formed for free electrons which move across to discharge the surfaces. Stored electric potential energy is dissipated as heat, light and sound. 

Q.  5.    If a solid dielectric is placed between the plates of a capacitor, its capacitance increases. Is there any other advantage of solid dielectric?

 Ans.     There are other two advantages of a solid dielectric. First, it helps in keeping the plates close together without touching. Secondly, we can now charge the capacitor to a higher potential (V = q/C).

 Q. 6.  Can you place a parallel plate capacitor (consisting of two plates) of 1 farad in your almirah? 

Ans.    No. Suppose the two plates of the capacitor are separated by as small a distance as 1 mm. (Ix10) Cd = (1)x 8.854x10 12 Eg A A = = 1.1 x 10 m? C = or d. This area is equal to the area of a square having each side more than 10 km. Modern technology, however, has permitted the construction of IF capacitors of very moderate size.

 Q .7.    Given a solid metal sphere and a hollow metal sphere. Which will hold more charge? Both spheres are of same radius.

 Ans.    Both the spheres will hold the same charge. It is because charge remains on the outer surface of a charged conductor (whether solid or hollow) and the spheres have equal surface areas. 

Q. 8.   Two capacitors of capacitance TuF and 0.01 µF are charged to the same potential. Which will give more intense electric shock if touched? 

Ans.    q = CV. Since V is constant, q a C. It means that capacitor having large capacitance will store more charge. Hence, when luF capacitör is touched, the discharging current will be high and you will get more intense electric shock than in case of 0.01µF capacitor. 

Q. 9.   Two spheres of different capacitances are charged to different potentials. They are then joined by a wire, Will total energy increase, decrease or remain the same?

Ans.      The two spheres are at different potentials. Therefore, when they are connected by a wire, there will be redistribution of charge (i.e., flow of charge through wire) till the two spheres attain the same potential. Due to the flow of charge through the connecting wire,

 Q 10.    Can there be potential difference between two adjacent conductors which carry the sitive charge? 

Ans.    Yes. We know that gC. The capacitance depends upon the dimensions of the ductor. If the two conductors are of different shapes and sizes, they will be charond different potentials when given the same charge.

 Q 11.     What are the differences between conductors and dielectrics? 

Ans.   (i) When a conductor is placed in an external electric field, there is no electric field inside the conductor. However, when a dielectric is placed in an electric field, its molecules are polarised. The cffect of this polarisation is to weaken the applied electric field within the dielectric,

 (ii) The dielectric constant of conductors is infinity while that of dielectrics is finite.

 (iv) The dielectric strength of conductors is zero while that of dielectrics is finite. 

(v) There is no limit to the current that a conductor can carry, provided cool enough. However, there is a limit to the electric flux that a dielectric will carry without breaking down. it can be kept .

Q. 12. Is the name condenser appropriate for a capacitor? 

Ans.   The name condenser is given to the device due to the fact that when p.d. is applied across it, the electric lines of force are condensed in the small space between the plates. In fact, a capacitor is a device used for "condensing' or accumulating the charge on plates. The term condenser is misleading and, therefore, the term capacitor is preferred.

 Q. 13. What is the need of multiplate construction in a capacitor?

 Ans.    C = E0 E, The capacitance of the capacitor can be increased by;

 (1) using dielectric of high ɛ, 

(ii) decreasing the distance between plates, 

(iii) increasing the plate area High cost limits the choice of dielectric and dielectric strength of the insulating material limits the reduction in spacing between the plates. The most convenient way of achiev- ing large capacitance is by using large plate area. Increasing the plate area may increase the physical size of the capacitor enormously. In order to obtain a large area of plate surface without using too bulky a capacitor, multiplate construction is employed. 

Q. 14.   Where do we use variable air capacitor? 

Ans. Variable air capacitor is a multiplate air capacitor whose capacitance can be varied by changing the plate area. It is commonly used to "tune in" radio stations in the radio receiver. The capacitance of such variable capacitors is from zero to about 4000 nF Q. 15. Why do capacitors connected in series result in less total capacitance? Ans, When capacitors are connected in series, they act as though we were adding to thick- ness of the dielectric. Whenever the spacing between plates is increased, the capacitance decreases. Even the formula for series-connected capacitors reveals this fact.

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