Experiment No. 5

The capacitor

The capacitor stores electric charge

Identifying Capacitor "Size"

If thr Farad "size" is not printed on the capacitor, you may find an EIA code listed. Use the table below to figure out the capacitance.

RC Time Delay or "Charging Time"

Capacitors take time to charge. It doesn't happen instantly. The charge time is dependent on the resistor in the circuit and the size of the capacitor. And it is expressed in the equation :

R x C x 5 = T. This is the time it takes to charge up to the applied voltage.

For example, 1,000,000 ohms x 0.000001 F x 5 = 5seconds to charge to applied voltage. This can also be expressed as 1M ohms x mF x 5 = 5 seconds.

Capacitors are often used for timing when events take place. And often the voltage only has to get up to about 2/3 the applied voltage, and this happens about 1/5 the time of their charging. So this is why the 5 is built into the equation. The concept of "time constants"is used here, where whatever the time it takes for a capacitor to built up to the full charge, it takes about 1/5 of that time to build up close to 2/3 of the charge. So you can divide the charge time into 5 segments, and the first time segment is often the time you are interested in.

Practice watching the capacitors charge up the inthe exercise below.

First calculate how much time it would take to charge up the capacitor. Then, connect the circuit as shown above. Measure the time taken by the capacitor to reach the applied voltage on an oscilloscope. Fill in the chart below. Also draw the observed waveforms in the graphs below, filling the details on each one.

The formula for calculating time

T = R x C x 5

0.0001 x 1000 x 5 = 0.5s

0.0001 x 100 x 5 = 0.05s

0.0001 x 470 x 5 = 0.235s

0.0003 x 1000 x 5 = 1.5s

How does changes in the resistor affect the changing time?

As the resistance increase the more time the capacitor takes to charge inorder to reach the maximum capacitance.

How does changes in the capacitor affect the changing time?

The bigger the capacitor is, the more time it will consume to charge up and it will also work for longer period of time compared to smaller capacitor when it is unplugged from the power source.