Caupayan, Jedda Anne G. BSEd-4
Physics
RC Circuit
Have you considered a circuit
with two electronic devices? In this chapter you will know a resistor and
capacitor present in one circuit. It is not very complicated but it requires
effort and time to get the data. Same in getting the data, you should also
require your time and effort in understanding the RC circuit.
Definition
RC circuit is a circuit with a
single capacitor and a single resistor. We already know that capacitor is a
two-terminal device whose voltage v(t) and current i(t). Take a look at this
relationship:
The equation
above shows that the current flowing in a capacitor is proportional to the rate
at which voltage changes across the device's terminals. The proportionality
constant, C is called the device's capacitance and it is measured in units
called farads.
Types of Capacitors
1. Ceramic Capacitor – one of the most common type of capacitors
-
shaped like a disk with two leads coming out of
it
2. Electrolytic Capacitor – constructed
using a paper soaked in an electrolyte
-
always have their polarity clearly marked, often
with a bunch of negative signs pointed at the negative terminal
Figure
1: Symbols and drawings of capacitors
To analyze the
circuit means that it is determining the voltage over the capacitor, vc(t),
(as a function of time).
This is the schematic
diagram of the RC circuit:
Figure 2: RC
Circuit
The first specific solution we'll consider is the voltage
over the capacitor under the assumption that the capacitor's initial voltage V0
is and the applied input voltage
is zero. Here is the formula:
This formula is
applicable if the time is greater than or equal to 0.
This is the relationship between the voltage and time of the RC circuit
Figure 3:Graph
for RC circuit (Charging)
Let's assume that V0=0 so that the capacitor is initially
uncharged. In this case another formula takes the following simplified form,
Figure 4: Uncharged capacitor
Formula:
T=RC
Applications:
RC's are often used as a timer of some sort.
Because the capacitor charges to the source voltage, and then discharges at a
constant and specific rate, it can be used as a time switch.
A good example is the intermittent wipers in your car, or the seek and scan function on a radio.
Explanation: When you turn your wipers on intermittent, that charges the capacitor and RC circuit to a certain voltage. As the capacitor discharges through the resistor, that voltage decreases. Once the voltage reaches a low limit, it triggers the wipers to move, and the capacitor recharges, and the whole cycle repeats.
Then can also be used to "rectify" a signal with some finite frequency into a smoother, constant, DC signal. They are often employed like this to "clean up" dirty or noisy signals, especially signals that are transmitted wirelessly. Cordless phones, remote controls, Stereo speakers and Amplifiers, etc.
A good example is the intermittent wipers in your car, or the seek and scan function on a radio.
Explanation: When you turn your wipers on intermittent, that charges the capacitor and RC circuit to a certain voltage. As the capacitor discharges through the resistor, that voltage decreases. Once the voltage reaches a low limit, it triggers the wipers to move, and the capacitor recharges, and the whole cycle repeats.
Then can also be used to "rectify" a signal with some finite frequency into a smoother, constant, DC signal. They are often employed like this to "clean up" dirty or noisy signals, especially signals that are transmitted wirelessly. Cordless phones, remote controls, Stereo speakers and Amplifiers, etc.
RC Circuit
I.
Objectives:
At
the end of this activity, we will be able to:
a. determine the voltage of the capacitor;
b. graph the data of the RC circuit
II.
Materials:
Voltage
regulator capacitor
Resistors stopwatch
multitester connecting wires
breadboard
III.
Procedure:
1. The resistance of the resistor is
determined.
2. The resistor and capacitor are set up
to form a circuit.
3. A certain voltage is applied from the
source to charge the capacitor.
4. The voltage is determined in every 5
seconds of charging until 1 minute is reached.
5. After 1 minute, the power is turned off
to discharge.
6. The voltage in every 5 seconds of discharging
is recorded.
IV.
Data and Result:
Table
1:
VOUT:
4.5 V , R1 = 5500 Ω , R2 = 180 Ω, C= 4700uF
t (s)
|
VDROP , Charging
|
VDROP, Discharging
|
Current, Charging
|
5
|
0.4 V
|
2.0 V
|
6.6 x 10-4 A
|
10
|
0.6 V
|
1.8 V
|
5.4 x 10-4 A
|
15
|
1.0 V
|
1.6 V
|
4.50 x 10-4 A
|
20
|
1.2 V
|
1.4 V
|
3.74 x 10-4 A
|
25
|
1.4 V
|
1.2 V
|
3.10 x 10-4 A
|
30
|
1.6 V
|
1.1 V
|
2.60 x 10-4 A
|
35
|
1.8 V
|
1.0 V
|
2.13 x 10-4 A
|
40
|
2.0 V
|
1.0 V
|
1.77 x 10-4 A
|
45
|
2.05 V
|
0.9 V
|
1.46 x 10-4 A
|
50
|
2.2 V
|
0.8 V
|
1.21 x 10-4 A
|
55
|
2.2 V
|
0.8 V
|
1.01 x 10-4 A
|
60
|
2.2 V
|
0.6 V
|
8.35x 10-5 A
|
V. Graphical Representation
.
Questions:
1. How does the voltage and current affect the charging time ?
Answer:Based on the activity,
we observed that as the time increases the voltage drop increses and also the
current increases.
2. How does the voltage affects the discharging time?
Answer: When it is discharging
the voltage drecreases.
VII.
GENERALIZATION:
Based on the activity, I learned that in
charging, the voltage increases as well as the current, in discharging the
voltage decreases as well the current.]
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