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Simple AC Flashcards

1
Q

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A

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2
Q

What is an A.C. circuit?

A

“Circuits through which an alternating current flows.”

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3
Q

Where are A.C. circuits used?

A

“Power transmission

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4
Q

How are alternating currents produced?

A

“By time dependent alternating voltages given by the relation E=E_{0} sin ωt.”

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5
Q

Does everything we learned about D.C. circuits apply to A.C. circuits?

A

“Much of what we learned about d.c. circuits also apply to a.c. circuits

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6
Q

What will this chapter discuss?

A

“The effect of such voltages on resistors

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7
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A

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8
Q

What are the learning objectives of this chapter?

A

“1. Explain the peak and r.m.s. values of current and p.d. 2. Establish the phase relationship between current and p.d in an a.c. circuit. 3. Explain reactance and impedance. 4. Determine current in circuits containing a. resistance and inductance; b. resistance and capacitance; and c. resistance

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9
Q

What is an Alternating Current (A.C.)?

A

“One that varies sinusoidally or periodically

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10
Q

How can the commonest form of A.C. be represented?

A

“I = I₀ sin 2πft = I₀ sin ωt”

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11
Q

In the equation I = I₀ sin 2πft = I₀ sin ωt, what do the variables represent?

A

“I = instantaneous current at a time t

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12
Q

How is alternating voltage represented?

A

“V = V₀ sin 2πft = V₀ sin ωt”

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13
Q

In the equation V = V₀ sin 2πft = V₀ sin ωt, what do the variables represent?

A

“V

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14
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15
Q

If an a.c. voltage is represented by the relation V = 4 sin 900πt, what is the peak voltage (V₀) and the frequency (f)?

A

“V₀ = 4 V and f = 900 / 2 = 450 Hz”

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16
Q

If an a.c. voltage is represented by the relation V = 4 sin 900πt, what is the angular velocity (ω)?

A

“ω = 2πf = 900π”

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17
Q

How does an alternating current (or voltage) vary?

A

“Sinusoidally”

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18
Q

What is the amplitude or peak value of the current (I₀)?

A

“The maximum numerical value of the current.”

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19
Q

What is the root-mean-square (r.m.s.) value of the current?

A

“The effective value of the current.”

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20
Q

What is the root mean square current?

A

“That steady current which will develop the same quantity of heat in the same time in the same resistance”

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21
Q

What is the formula for the r.m.s. value of the current?

A

“I_{r.m.s.} = I₀ / √2 = 0.707I₀”

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22
Q

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A

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23
Q

What do moving iron and hot-wire meters measure?

A

“The average value of the square of the current called the mean-square current.”

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24
Q

How are moving iron and hot-wire meters calibrated?

A

“To indicate the r.m.s. current directly.”

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25
What values do most a.c. meters read?
"The effective or r.m.s. values."
26
What is the average value of an a.c. voltage or current?
"Zero."
27
What does Fig 8.2 show?
"A simple a.c. circuit."
28
What is the symbol of an a.c. voltage source?
"As shown in fig 8.2a (a sine wave within a circle)."
29
In Fig. 8.2, what is the current through the resistor (R) and the voltage across it?
"I and V
30
What is the relationship between V, I, and R?
"V = IR"
31
Front
Back
32
What does the voltmeter and ammeter connected in the circuit read?
"The r.m.s. values of voltage and current."
33
How is the relationship between r.m.s. voltage, r.m.s. current, and resistance expressed?
"I_{r.m.s.} = V_{r.m.s.} / R"
34
What is the phase relationship between voltage and current in a purely resistive A.C. circuit?
"The voltage and the current are said to be in phase or in step with each other."
35
What does it mean for voltage and current to be in phase?
"Both of them attain their maximum
36
What is shown in Fig. 8.3a?
"A simple circuit where an a.c. voltage is connected in series with a capacitor of capacitance C (Farads)."
37
In Fig. 8.3a, are the voltage (V) and current (I) in phase?
"No
38
In a capacitive A.C. circuit, which leads and which lags?
"The current is said to lead on the voltage and the voltage is said to lag on the current."
39
What is the phase difference between the current and the voltage in a capacitive A.C. circuit?
"90° or (π/2) radians."
40
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41
If V = V₀ sin ωt, then what is the equation for current (I) in a capacitive A.C. circuit?
"I = I₀ sin(ωt + π/2)"
42
What is the opposition to the flow of a.c. offered by the capacitor called?
"Capacitive reactance (X_c)."
43
What is the formula for capacitive reactance (X_c)?
"X_c = 1 / (2πfC)"
44
When an a.c. voltage of frequency f is applied to a capacitance C, how is the voltage related to the current and reactance?
"V = I X_c"
45
In the equation V = I X_c, what replaces resistance (R)?
"X_c"
46
What is the unit of X_c?
"Ohms."
47
What is the value of X_c in Example 8.1?
"1324.4 Ω"
48
What is the r.m.s. value of the current in Example 8.1?
"0.113 A"
49
What is the peak value of the current in Example 8.1?
"0.160 A"
50
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51
In Fig 8.4a, what is connected across an inductor L?
"An a.c. voltage."
52
What does the sinusoidal voltage cause to flow?
"A sinusoidal current."
53
What does the induced e.m.f in the inductor L oppose?
"The change in the current."
54
What is the result of the induced e.m.f. opposing the change in current?
"The current is delayed behind the voltage in the circuit."
55
By how much does the current I lag behind V?
"π/2 radians or 90° or by 1/4 cycle."
56
If V = V₀ sin ωt, then what is the equation for current (I) in an inductive A.C. circuit?
"I = I₀ sin(ωt - π/2)"
57
What is the impedance effect of an inductor L called?
"Inductive reactance (X_L)."
58
How is voltage related to current and inductive reactance?
"V = I X_L"
59
What is the unit of X_L?
"Ohms."
60
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61
What is the formula for inductive reactance (X_L)?
"X_L = 2πfL"
62
In the formula X_L = 2πfL, what are the units of L and f?
"L is in henrys (H)
63
What is reactance?
"The opposition to the flow of a.c
64
What is the impedance (inductive reactance) across an inductor of 0.2 H inductance when an a.c. voltage of 60 Hz is applied across it? (Example 8.2)
"75.40 Ω"
65
In Example 8.2, if the voltage is given by V = 150 sin 120πt, what is the r.m.s. value of the current?
"1.39 A"
66
In Example 8.2, if the voltage is given by V = 150 sin 120πt, what is the peak value of the current?
"1.99 A"
67
What is connected in series in Fig. 8.5?
"A Resistance (R)
68
If an alternating voltage V = V₀ sin 2πft is put across the circuit in Fig. 8.5, what will flow along the circuit?
"A steady state current given by I = I₀ sin 2πft"
69
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70
What is the formula for the maximum or peak value of the current (I₀) in a series RLC circuit?
"I₀ = V₀ / [R² + (X_L - X_c)²]^½ = V₀ / √(R² + X²)
71
What is Z?
"The Impedance of the circuit."
72
What is the formula for Impedance (Z)?
"Z = [R² + (X_L - X_c)²]^½ = √(R² + X²)"
73
How is the maximum or peak current (I₀) related to the peak voltage (V₀) and Impedance (Z)?
"I₀ = V₀ / Z"
74
How is the r.m.s. current (I_rms) related to the r.m.s. voltage (V_rms) and Impedance (Z)?
"I_{r.m.s.} = V_{r.m.s.} / Z"
75
What is Impedance (Z)?
"The overall opposition of a mixed circuit containing a resistor
76
What is the unit of Impedance (Z)?
"Ohms."
77
Front
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78
From equation (8.7), what is the formula for X_c?
"X_c = 1 / (ωC) = 1 / (2πfC)"
79
From equation (8.10), what is the formula for X_L?
"X_L = ωL = 2πfL"
80
How can Impedance (Z) be written in terms of R, ω, L, and C?
"Z = √(R² + (ωL - 1/(ωC))²) = √(R² + (2πfL - 1/(2πfC))²)"
81
What are the voltages across R, L, and C?
"V_R = IR
82
What is the formula for the total voltage (V) in a series RLC circuit?
"V = IZ = I[R² + (X_L - X_c)²]^½"
83
What is the r.m.s. value of an alternating current whose peak value is 5 amps? (Example 8.3)
"3.53 Amps"
84
In an a.c. circuit, if the peak value of the potential difference is 180 V, what is the instantaneous p.d. when it has reached 1/8th of a cycle? (Example 8.4)
"90√2 Volts"

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