Download Experiment 1: Description of a capacitor

Tuesday 1/12/2009
Electric circuit lab -EENG 301L Section : D
Group # 2
Third report.
Written By:
Ali Ibrahim
Group
Abbass Taher
Hassan Amhaz
Ali Ibrahim
Instructor Dr: Nadine Rustom.
Fall 2009-2010
Equipments:
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Connecting wires.
Com3lab (70012DC2)
Objectives:
Experiment 1: Description of a capacitor:
To know the function of the capacitor,we do a little discreption about it.
For this reason.we perform the following circuit:
The capacitance of a plate capacitor depends on the plate spacing,the material
between the plates and the area of the plates.
For this instance,the experiment shows that when the body is charged,the voltage
with respect to a reference point(ground) is proportional to the supplied charge.
This proportional factor is termed the capacitance of the body.It indicates the
body’s capacity to store charges.
This property is made use of in components called capacitors.
Experiment 2: Charging of a capacitor:
In the same circuit:
In this case, the capacitor C1 is charging. The multimeter 2 measures the voltage
across the capacitor C1,this voltage is increasing with respect to the time and the
curve that is responsible for the charging of the capacitor is increasing as follows:
The time response of the voltage measured across the capacitor can be used to
determine the Time Constant τ of the capacitor. The capacitance of the charged
capacitor can be determined as well.
To determine the time constant τ we draw a tangent on the curve at time t=0
and another line parallel to time axis and passes through the maximum values of
the curve. These 2 lines intersect at a point,the abscissa value of this point is the
time constant τ.
For a caoacitor to be fully charged,it takes 5 τ.
Experiment 3: Discharging of a capacitor:
8-Capacitors in parallel:
Case of charging:
To know the connection of the parallel capacitors,we do the following circuit:
The time response of the voltage measured across the capacitor pair can be use
to determine the time constant τ . The total capacitance of the
charged,parallel-connected capacitors can be determined as well.
Case of discharging:
When the second capacitor is connected in parallel with the capacitor of an RC
circuit,the time constant decreases.
Then the equation of the capacitors when they are connected in parallel is:
Ceq = C1 + C2 + … + Cn
9-capacitors in series:
Case of charging:
To know the connection of the capacitors in series,we do the following circuit:
The charging characteristic of the capacitors is then measured.
The time response of the voltage measured across the capacitor pair can be used
to determine the time constant τ.
The total capacitance of the charged,series-connected capacitors can be
determined as well.
Then the equation of the capacitors when they are connected in series is:
1/C eq = 1/C1 + 1/C2 + …+ 1/Cn
Case of discharging:
10 - RC Combinations:
The time constant
τ
of a series-connected capacitor and resistor depends on the
capacitance C and resistance R.
The voltage characteristic of the capacitor during discharge can be used to
determine τ ,the time taken for the voltage to drop to 37%.
The time response of the series-connected resistor-capacitor during discharge is
determined here:
Discharging of the capacitor. The time characteristic of the voltage is recorded
here during discharge via four different resistors. From the time characteristic of
the capacitor, you can determine the time constant τ of each RC element.
The values are in this table:
11-Inductance:
The voltage response in the coil during switch-on and switch-off is observed with
the help of the glow lamp. The diode is then acts as a free-wheeling diode.
When the electrical circuit is closed,the glow lamp remains unlit because the
voltage is too low.when the switch is opened,the lamp flashes because the rapidly
If the diode is connected in parallel with the coil,the lamp always remains unlit.
When the power is turned on,the diode blocks the current,when the power is
turned off,a self-induced current of opposite polarity flows out through the diode.