Charging and Discharging of capacitor

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Aim:-

To determine the value of the time constant of the given capacitor by drawing it’s charging and discharging curves.

Apparatus:-

DC supply, Voltmeter, Stop clock, Capacitor and Resistor. 


Circuit Diagram:-

Circuit Details:- 

1) K1 and K2= Key

2)B=Battery

3)R=Resistance 

4)C= capacitor 

5)o/p= output


Theory:-

A capacitor is a passive device that stores electrical energy as electrical charges and returns energy to the circuit whenever required.

When a capacitor is connected to a circuit with direct current (DC) source, two processes which are called charging and discharging will takes place in specific condition.

A capacitor is connected to Dc power supply and current flows through the circuit. Both plates get the equal and opposite charges and on increasing potential difference Vc is created while the capacitor is charging. Once the voltage at terminals of the capacitor Vc is equal to the power supply voltage VC=V, the capacitor is fully charged and current stops flowing through the circuit, the charging phase is over. A capacitor is equivalent to an open circuit or DC i.e. R=infinity because once the charging phase has finished, no more current flows through it. The voltage Vc on a capacitor can’t change abruptly. When the capacitor disconnected from the power supply, the capacitor is discharging through the resistor Ro and the voltage between the plates drops down gradually at Zero, Vc=0.

The resistance of Rc and Rc affect the charging rate and discharging rate of the capacitor respectively. The product of resistance R and capacitor C is called the time constant T, which characterizes the rate of discharging of a capacitor.

Procedure:-

1)   Connections’ are made as shown in the figure.

     2)   Keys K1 and K2 kept open. The DC power supply V is switched on.

     3)   Key K1is closed and simultaneously the stop clock is started.

     4)   The voltage across the capacitor is noted at time intervals o 30-sec unit it reaches the maximum steady value,(Vo)

     5)   Now the K1 is opened and the stop clock is reset. 

     6)   Voltage across the capacitor at t=0 sec and then at time interval 30 sec are noted until it reaches a steady minimum value.

     7)   Graphs are plotted taking the along X-axis and voltage along the y-axis during charging and discharging of the capacitor.

     8)   In the charging graph, note time corresponding to the value of V=0.637Vo

     9)   In the discharging curve note time corresponding to the voltage values 0.37Vo.

     Tabular column:-

For Charging

 Sl. No

 Time in second

 Voltage in volts

 

 

 

 

 

 









For Discharging

 Sl. No

 Time in second

 Voltage in volts

 

 

 

 

 

 







     Nature of Graph:-




Calculation:-

Maximum voltage Vo=……..

For charging T= 6.637×VO=……….

For discharging T=0.37×VO=………..


Result:-

Charging the time constant for the given capacitor is=……….

Discharging time constant for the given capacitor is=……..


 

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