7. An ideal parallel-plate capacitor consists of a set of two parallel plates of
ID: 779294 • Letter: 7
Question
7. An ideal parallel-plate capacitor consists of a set of two parallel plates of area A separated by a very small distance d. When the capacitor plates carry charges +Q and -Q, the capacitor stores energy Uo. If the separation between the plates is QUADRAPOLE, how much electrical energy is stored in the capacitor? a) 4Uo b) 200 c) Uo d) Uo/2 e) Uo/4 8. A cylindrical wire has a resistance R and resistivity p. If its length and diameter are BOTH cut in half, what will be its resistance? a) 4R b) 3R c) 2R d) R e) R/4 9. A cylindrical wire has a resistance R and resistivity p. If its length and diameter are both DOUBLED, what will be its resistivity? a) 4p b) c) 2p d) p/2 e) p/4 When a potential difference of 10 V is plac it is 2 A. If the diameter of this resistor is now tripled, the current will be 10. ed across a certain solid cylindrical resistor, the current through a) 2/9 A b) 2/3 A c) 2 A. d) 3 A e) 18A. 11. Determine the resistance of 35 m long copper wire. The cross sectional area of the wire is 5.2x10m Resistivity of copper is 1.72x1 2.m a) 1.22 b)2.232 ) 3.2 2 d)4.22 ) 5.262Explanation / Answer
8)R=resistivity*length/area
if length and diameter,both are reduced to half, length/area will become twice of the initial value.
Therefore resistance will become twice the initial value
Correct option is 2R
9)Resistivity is a material property and does not depend on dimensions of wire. Therefore the resisticity will remain unchanged. Correct option is (b)
10)if the diameter of the wire is tripled, the resistance of wire will become R/9
if the initial current is I, the new current for the same potential difference will be 9*I
in the given scenario, initla current = 2 A
new current will be 9*2=18 A
11)Resistance= 1.72*10-8*35/(5.2*10-7)=1.16=1.2 Ohms
Correct option is (a)
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