RC circuit.pptx

rc

1. RC Circuit –Time constant

2. RC Circuit – Time constant Aim: To study decay of charge in an RC circuit and determine RC time constant   Apparatus: Board Consisting of DC Power supply, switch, Ammeter/ Voltmeter, combinations of Resistors and Capacitors, stop clock and connecting wires.   Theory: When a condenser ‘C’ is charged through resistance ‘R’ then charge increases with time exponentially and is given by the equation, Q(t) = Q (1-e -t/RC ). At t = RC (seconds), then Q = 0.632 Q . Where Q is the maximum charge.

3. The product ‘CR’ is called time constant . It is equal to the time taken to establish 0.632 times or 63% part of the final charge Q o Q = Q o e -t/RC .   The time constant in this case is equal to the time taken for the charge to get reduced to 1/e part of the maximum charge. It is equal to the time taken to discharge to a value of 0.368 part or 36% of the maximum charge. (Q /e =0.368 Q ). We know I = dq / dt , I = I e –t/RC (amps).   W hen T c = RC , I = 0.368 I 0.   Where C = capacitance in farads, R = resistance in ohms, I = current in amperes.

4. Procedure:   The circuit is connected as shown in figure choosing one set of Rand C values. The capacitor C is charged for a short time by pushing the charging switch up, till the deflection in the ammeter is maximum but within the scale. The tap key is then pushed down. The capacitor now starts getting discharged through the resistor R. The stop clock is started and readings of the ammeter are noted at an interval of five seconds. The experiment is repeated for the other values of R and C. The observations are tabulated.

5. Observations : R=________Ω, C=__________F, T C =RC=___________ sec. Table : Time (Sec) Discharging Current (  A)

6. R(ohm) C(farad) T c (Experimental OR graphical Value) T c (Theoretical including error) sec sec Result:

7. End of the Experiment