Physics · University
RC discharge voltage
Ideal RC discharge with no driving source. Convert kilohms and microfarads consistently.
Method and conditions
Ideal RC discharge with no driving source. Convert kilohms and microfarads consistently.
V(t) = V₀ exp[−t/(RC)]
Worked examples
An ideal capacitor initially at 14 V discharges through 48 kΩ. C=170 μF. Find the capacitor voltage at t=1.8 s. Round the final result to 4 decimal places if needed. Answer in V.
RC = (48×1000)(170×10⁻⁶) = 8.16 s; substitute into V₀ exp(−t/RC).
11.2287 V
An ideal capacitor initially at 3 V discharges through 36 kΩ. C=300 μF. Find the capacitor voltage at t=1.4 s. Round the final result to 4 decimal places if needed. Answer in V.
RC = (36×1000)(300×10⁻⁶) = 10.8 s; substitute into V₀ exp(−t/RC).
2.6353 V
Try it
An ideal capacitor initially at 4 V discharges through 18 kΩ. C=170 μF. Find the capacitor voltage at t=1.4 s. Round the final result to 4 decimal places if needed. Answer in V.
An ideal capacitor initially at 16 V discharges through 12 kΩ. C=50 μF. Find the capacitor voltage at t=0.9 s. Round the final result to 4 decimal places if needed. Answer in V.
Check your work
Answers and marking notes
- 2.5314 V
RC = (18×1000)(170×10⁻⁶) = 3.06 s; substitute into V₀ exp(−t/RC).
- 3.5701 V
RC = (12×1000)(50×10⁻⁶) = 0.6 s; substitute into V₀ exp(−t/RC).
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