1. ALTERNATING CURRENT AND VOLTAGE
PHYSICS
SMK PERGURUAN CIKINI

2. FORMULATION OF ALTERNATING CURRENT AND VOLTAGE
The equation of e and v above is anologues with the deviation equation of simple harmonic motion, that is, x = A sin wt.
According to formula, then alternating voltage has frequency and period as in simple harmonic motion. In this case, the frequency and period of the alternating voltage relate to the repeation of the maximum or minimum state of voltage value.
The quantity of frequency and period in alternating voltage can be determined bay the following equation:
and
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3. FORMULATION OF ALTERNATING CURRENT AND VOLTAGE
Therefore, the equation of alternating voltage can be expressed as follows: or
If the alternating voltage is set in a circuit, then the current flowing in the circuit is also alternating current which varies to time according to the sine function. Therefore, alternating current can be represented in the equation as follows: or
Note:
T = period (s)
f = frequency (Hz)
w = the anguler speed (rad/s)
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4. THE EFFECTIVE VALUE OF ALTERNATING VOLTAGE AND CURRENT
The value of alternating current or voltage which is assumed equivalent with the direct current or voltage is called effective value of alternating current or voltage.
and
Note:
I = effective value of alternating current (A)
Imax = maximum current (A)
v = effective value of alternating voltage (volt)
vmax = maximum voltage (volt)
The effective value of alternating current and voltage can be measured using instruments such as AC amperemeter and AC galvanometer (for current) and AC voltmeter (for voltage).
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5. FORMULATION OF ALTERNATING CURRENT AND VOLTAGE
Example
An AC voltmeter is connected to the AC voltage source shown the value of 110 volt, calculate:
maximum voltage (vmax)?
effective current flowing through the resistor of 50 W which
is connected to the voltage source? 
50 W
110 V
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6. FORMULATION OF ALTERNATING CURRENT AND VOLTAGE
Solution
Vef = 110 volt
R = 50 W
Vmax = ….?
Ief = ….? a.
Thus, the maximum voltage is b.
Thus, in R = 50 W flows current of 2.2 A
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7. ALTERNATING CURRENT CIRCUIT
Resistive circuit  R V
Because the resistive circuit is assumed has no inductance and capacitance, then the circuit is not influenced by the change of magnetic field around it. For that reason, then in this circuit, the alternating current and voltage have the same phase or their phase difference is zero. This state can be describe by phase function graph of current and voltage as besides.
V, I
180
360
540
720 wt
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8. ALTERNATING CURRENT CIRCUIT
Inductive circuit  L V
In the induction circuit, electric current has different phase with voltage. This case, voltage V precedes current I with phase difference of p/2 or 90o. This state can be described by the phase angle function graph of current and voltage as besides.
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INDUCTIVE CIRCUIT
Although in inductive circuit there is no resistor, but in this circuit there is quantity which has the same characteristic with the electric resistance, that is inductive reactance, which the value can be determined as follows:
Note:
XL = inductive reactance (W)
f = frequency (Hz)
w = the anguler speed (rad/s)
L = inductance of inductor (H)
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10. ALTERNATING CURRENT CIRCUIT
Capacitive circuit
According the equation I and V above, then in capacitive circuit, electric current has phase difference of p/2 to the voltage. This case, current I precedes voltage V with phase difference of p/2 or 90o. This state can be described by the phase angle function graph of current and voltage as besides.  C V
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11. ALTERNATING CURRENT CIRCUIT
As inductive circuit, then in capacitive circuit there is a reactance quantity called capacitive reactance and the value can be determined as follows:
Note:
XL = capacitive reactance (W)
f = frequency (Hz)
w = the anguler speed (rad/s)
C = capacitance of capacitor (F)
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12. SERIES COMBINATION CIRCUITS
Series R-L circuit
If the series combination between resistor R and inductor L is set to the alternating voltage source, then the inductor voltage VL precedes current I with phase difference of 90o, while resistor voltage VR has the same phase with current I. This state can be illustrated by the phasor diagrams as besides.  R L VR VL V VL VR V  I
Note:
Z = impedance (W)
j = phase difference
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13. SERIES COMBINATION CIRCUITS
Series R-C circuit
If the series combination between resistor R and inductor L is set to the alternating voltage source, then the capacitor voltage VC is left by the current I with phase difference of 90o, while resistor voltage VR has the same phase with current I. This state can be illustrated by the phasor diagrams as besides.  R C VR VC V Vc VR V  I
where
Z = impedance (W)
j =phase difference
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14. SERIES COMBINATION CIRCUITS
Series R-L-C circuit
When the series combination of resistor R, inductor L and capacitor C are connected to the AC voltage source, then the resistor voltage VR has the same phase with current I, the inductor voltage VL precedes current I with phase difference of 90o, and the capacitor voltage VC is left by the current I with phase difference of 90o. This state can be illustrated by the phasor diagrams as follows:  R L VR VL V C VC
VL- VC VR V  I VC
- VC VL
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RESONANCE
The series R-L-C circuit is in the resonance state if the value of inductive reactance XL is equal to the value of capacitive reactance XC, so that in this state XL-XC = 0 or impedance of the circuit is equal to the resistance (Z = R).
Besides that in the resonance state holds I = V/R, it’s because Z = R.
Note:
L = inductance of inductor (H)
C = capacitance of capacitor (F)
f = frequency (Hz)
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16. POWER IN ALTERNATING CURRENT CIRCUIT
In the alternating current circuit, its power can be determined by the equation as follows:
Note:
P = power (watt)
Ief = effective value of alternating current (A)
R = the resistor (W)
VR = the resistor voltage (volt)
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17. ALTERNATING CURRENT CIRCUIT
Example
Look at the following figure of series R-L-C circuit:  R L C
If the resistance R = 40 W, inductance L = 8 H and capacitance C = 8 mF are set on the voltage source which has the effective voltage of 110 volt and the angular speed of 375 rad/s, then calculate:
1. the effective current in the circuit?
2. the power in the circuit?
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18. ALTERNATING CURRENT CIRCUIT
Solution
a. effective current (Ief)
R = 40 W
Then,
Thus, the effective current in the circuit is 2.2 A
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19. ALTERNATING CURRENT CIRCUIT
b. Power (P)
Thus, the power in the circuit is watt
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EXERCISE
1. A coil has inductance of 0.04 H. Determine:
Its inductive reactance if it is connected to the AC voltage
which has angular frequency of 10 rad/s?
b. the maximum current strength when its voltage of 20 volt?
2. A capacitor has capacitance of 12.5 mF and connected in series
with resistance of 60 W then connected to the AC voltage of 120
volt. If the angular frequency is 1000 rad/s, calculate the current
strength and phase difference between V and I in the circuit?
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EXERCISE
3. the series R-L-C circuit has R = 300 W, L = 0.6 H and C = 5 mF
are connected to the AC voltage source which has angular
frequency of 1000 rad/s. Calculate:
impedance of circuit?
self inductance if occurs resonance?
Phase difference between V and I?
4. look at the circuit the following figure! 
R=400W
L=0.5 H
C=5 mF
V = 100 sin(1000t) volt
Calculate:
effective current in the circuit?
power in the circuit?
power faktor?
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thank you
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