AC SIGNAL‘S ACTION TO RC, R L CIRCUITS
I.Learning Objectives:
a. Define equivalent resistance of RC circuit
b. Define equivalent resistance of RL circuit
c. Calculate the phase difference of 2 signals.
II.Theory:
Current I(t) and potential difference U(t) in an AC circuits are defined by using Oscilloscope in 2
channel mode. A function generator S
12
is used as a voltage source which has U
0
amplitude and variable
frequency f. Measurements are used to calculate average v
AC SIGNAL‘S ACTION TO RC, R L CIRCUITS
I.Learning Objectives:
a.
Define equivalent resistance of RC circuit b.
Define equivalent resistance of RL circuit c.
Calculate the phase difference of 2 signals.
II.Theory:
Current I(t) and potential difference U(t) in an AC circuits are defined by using Oscilloscope in 2 channel mode. A function generator S
12
is used as a voltage source which has U
0
amplitude and variable frequency f. Measurements are used to calculate average value of equivelent resistor follow expression: Z = U
0
/ I
0
and the phase difference
between current and potential difference. Alternatingcurrent circuit (AC) theory:

If circuit has only resistor, current and potential difference between 2 terminal of resistor have the same phase

If AC circuit has only inductions, current’s phase is
/2 later than potential difference ‘s phase

If AC circuit has only capacitor, current’s phase is
/2 sooner than potential difference ‘s phase
2.1. AC Circuits have resistor and capacitor in series
RC circuit in series:

Use current as a srcin.

Potential difference between 2 terminal of resistor and current the same phase

Potential difference between 2 terminal of capacitor is
/2 later than current . AC current : i = I
0
. Sin(
t) Potential difference on R : u
R
= U
0RSin
(
t) Potential difference on C : u
C
= U
0CSin
(
t 
/2) Potential difference on RC : u = U
0
Sin (
t +
)
With:
is the phase difference between potential difference and current’s amplitude in circuit.
can be calculated from phase diagram Potential difference on RC : u = U
0
Sin (
t +
)
With:
is the phase difference between potential difference and current’s amplitude in circuit.
can be calculated from phase diagram. In series RC circuit: u = u
R
+ u
C
RC circuit in series
Gi
ản đồ
pha c
ủ
a mch RL n
ố
i ti
ế
Phase diagram of RC circuit in series
And U
2
=U
2r
+U
2c
U
2
= I
2
(R
2
+ 1/(
.c)
2
) So that, we can definde summary resistance of RC circuits in series:
222
.1
C R Z
Phase difference between potential difference and current’s amplitude in circuit is tg (
) =
L RU U
RC
..1
Summary: if we know U
R
, U
C ,
and phase difference
, we can find current and equivalent resistance in circuit..
2.2. AC Circuits have resistor and inductor in series
RL circuit in series:

Use current as a srcin.

Potential difference between 2 terminal of resistor and current the same phase

Potential difference between 2 terminal of inductor is
/2 sooner than current .
RL circuit in series
AC current : i = I
0
. Sin(
t) Potential difference on R : u
R
= U
0RSin
(
t) Potential difference on L : u
L
= U
0LSin
(
t +
/2) Potential difference on RL circuits : u = U
0
Sin (
t +
)
With:
is the phase difference between potential difference and current’s amplitude in circuit.
can be calculated from phase diagram With RL sreial circuit: u = uR + u
L
And U
2
=U
2r
+U
2L
U
2
= I
2
(R
2
+ (
.L)
2
) So that, we can definde summary resistance of RL circuits in series:
222
.
L R Z
Phase difference between potential difference and current’s amplitude in circuit is tg (
) =
R LU U
R L
.
Summary: if we know U
R
, U
L ,
and phase difference
, we can find current and equivalent of resistor in circuit..
2.3. AC Circuits have inductor and capacitor in series Phase diagram of RL circuit in series

Use current as a srcin.

Potential difference between 2 terminal of capacitor is
/2 later than current .

Potential difference between 2 terminal of inductor is
/2 sooner than current AC current : i = I
0
. Sin(
t) Potential difference on L : u
L
= U
0LSin
(
t +
/2) Potential difference on C : u
C
= U
0CSin
(
t 
/2) Potential difference on RL circuit : u = U
0
Sin (
t +
) So that: U = U
L
– U
C
Summary: The phase difference is
/2 if UL
is greater than UC. And phase difference is
=
/2 if UL
is smaller than UC.
III.Apparatus
3.1 Define equivalent resistance of RL circuit
Order Equipments Quantity
1 A4 Test board 1 2 Resistor STE 1
, 2W 1 3 Resistor STE 100
, 2W 1 4 Resistor STE 10k
, 0.5W 1 5 500 turns coil 1 6 1000 turns coil 1 7 Funtions Generator S12 1 8 Oscilloscope 303 1 9 Jack 2 10 Wire 1 11 Multimeter 2
3.2. Define equivalent resistance of LC circuit
Order Equipments Quantity
1 A4 test board 1 2 Resistor STE 10
, 2W 1 3 Resistor STE 100
, 2W 1 4 Capacitor STE 1
F, 100V 1 5 Capacitor STE 4.7
F, 63V 1 6 500 turns coil 1 7 1000 turns coil 1 8 Funtions Generator S12 1 9 Oscilloscope 303, 1 10 Jack 2 11 Wire 1 12 Multimeter 2
IV.
Experimenting
4.1 Define standard for Oscilloscope in 2 channel mode. 4.1.1. Function Generator.
 Connect Multimeter to the output port of function Generator for measuring different potential and frequency.  Adjust amplitude and frequency in function generator to get the signal with 5000Hz frequecy and 2V different potential at out put ports.
4.1.2. OCR HM 3036.
Hình 5.1: Function buttons of OCR HM 3036