**
RC Circuits Examples**

Example #1

The circuit below
has been in position * a* for a long time.
At time

a.) What is the curnent through the resistor just BEFORE the switch is thrown?

**I*** = *0

b.) What is the current through the resistor just AFTER the switch is thrown?

Solution: **I = V/R**

**I*** = *0.6* *amps

c.) What is the charge across the capacitor just BEFORE the switch is thrown?

Solution: **Q = CV**

**Q*** = *120* **m**C*

d.) What is the charge on the capacitor just AFTER the switch is thrown?

Solution: Charge does not change instantaneously.

**Q*** = *120* **m**C*

e.) What is the
charge on the capacitor at at time * t *=

Solution: **Q = Q**_{0}**exp(-t/****t****) ,** where** ****t**** **=** RC **= 0.2 msec

**Q*** = *26.8* **m**C*

Example #2

Considering the
same circuit, only with the switch thrown from * b*
to

a.) What is the curnent through the resistor just BEFORE the switch is thrown?

**I*** = *0

b.) What is the current through the resistor just AFTER the switch is thrown?

Solution: **I = V/R**

**I*** = *0.6* *amps

c.) What is the charge across the capacitor just BEFORE the switch is thrown?

Solution: **Q = CV**

**Q*** = *0* *

d.) What is the charge on the capacitor just AFTER the switch is thrown?

Solution: Charge does not change instantaneously.

**Q*** = *0* *

e.) What is the
charge on the capacitor at at time * t *=

Solution: **Q = Q**_{0}**(1.0
- exp(-t/****t****)) ,** where** ****t**** **=** RC **= 0.2 msec

**Q*** = *93.2* **m**C*