A 4mf capacitor is charged by a 200 V battery. It is then disconnected from the supply and is connected to another uncharged 2mf capacitor. During the process loss of energy (in J) is ?
The initial energy stored in the 4mf capacitor is:
E = 1/2 * C * V^2
E = 1/2 * 4 * 10^-6 * (200)^2
E = 8 * 10^-2 J (to 2 decimal places)
When the 4mf capacitor is connected to the 2mf capacitor, they form a circuit with a total capacitance of 6mf. The total charge on the capacitors will stay the same, but the voltage across them will be split in proportion to their capacitances, so:
Q = C1 * V1 = C2 * V2
V2 = C1/C2 * V1
V1 + V2 = 200
Substituting C1 = 4mf and C2 = 2mf gives:
V1 = 2/3 * 200 = 133.33 V
V2 = 1/3 * 200 = 66.67 V
The final energy stored in the capacitors can be calculated using:
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Verified answer
Explanation:
The initial energy stored in the 4mf capacitor is:
E = 1/2 * C * V^2
E = 1/2 * 4 * 10^-6 * (200)^2
E = 8 * 10^-2 J (to 2 decimal places)
When the 4mf capacitor is connected to the 2mf capacitor, they form a circuit with a total capacitance of 6mf. The total charge on the capacitors will stay the same, but the voltage across them will be split in proportion to their capacitances, so:
Q = C1 * V1 = C2 * V2
V2 = C1/C2 * V1
V1 + V2 = 200
Substituting C1 = 4mf and C2 = 2mf gives:
V1 = 2/3 * 200 = 133.33 V
V2 = 1/3 * 200 = 66.67 V
The final energy stored in the capacitors can be calculated using:
E = 1/2 * C * V^2
E = 1/2 * 4 * 10^-6 * (133.33)^2 + 1/2 * 2 * 10^-6 * (66.67)^2
E = 2.963 J (to 3 decimal places)
The loss of energy during the process is the difference between the initial and final energies:
Loss of energy = 8 * 10^-2 - 2.963
Loss of energy = 0.07037 J (to 3 decimal places)