Discharging a capacitor
Warning :
Before connecting the capacitor make sure it's discharged by short-circuiting it.
To discharge the capacitor, disconnect the voltage source by turning the switch to position 2, and start counting time with a stopwatch simultaneously with disconnecting the voltage source. the capacitor discharges over time through the resistance R,
Note :
Read the voltage of the capacitor terminal each 5 seconds and record the values in the following table.
\(t(s)\) | 00 | 05 | 10 | 15 | 20 | 25 | 30 | 35 | 40 | 45 | 50 |
\(U_c(V)\) | 0 | 3.85 | 2.92 | 2.00 | 1.52 | 1.12 | 0.62 | 0.28 | 0.1 | 0.02 | 0.02 |
Required work
a- On graph paper, plot the voltage Uc= f(t)
b- Determine the time constant, τ = RC; the abscissa of the point of intersection of this tangent with the limit voltage of the load
c- From the time constant ensure the value of C.
Method :
Plot the tangent to the origin point and determine the time constant
Simulation :
In this graph we found τ is 7.5s which is close to the calculated one τ = RC = 7.2s
