A capacitor is constructed of identical parallel plates, each of area A = 3 m^2,
ID: 581175 • Letter: A
Question
A capacitor is constructed of identical parallel plates, each of area A = 3 m^2, that overlap only halfway as shown above. The spacing is d= 2 cm. Neglect the fields at the edges of Suppose a charge of Q= 5.10^-8 C is placed on the capacitor. The voltage is then V_1 ; then the plates are moved without changing the spacing, so that now they overlap complete across them is now measured to be V_2. The values V-1 and V-2 are then V_1 = V V_2 = V The plates of the capacitor in the above question are now connected to a V_battery = 18Volt battery. The plates are initially separated, with 50% overtop, as shown in the Figure e plates are moved (parallel to each other with the spacing between them kept constant and still connected to the battery) so that their overlap is 100%, Charge is drawn from the battery, leaving Q = 4.8 times l0^8 C on the capacitor. The potential across the capacitor drops to 9V. Charge is drawn from the battery, leaving Q = 2.4 times 10^-8 C on the capacitor.Explanation / Answer
C1=8.85*10^-12*1.5/0.02=6.637*10^-10F
V1=Q/C1=5*10^-8/(6.637*10^-10)=75.335V
V2=Q/C2=Q/(2*C1)=75.335/2=37.67V (Since area is doubled (from 1.5 to 3),C2=2*C1 )
2)When connected to battery V=constant
Q1=C1*V=6.637*10^-10*18=1.194*10^-8C
Q2=C2*V=2*C1*V=2*Q1=2.38*10^-8C
3rd option correct
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