Magnetism & Electromagnetism
What happens to magnetic flux if the area of a loop increases while the field stays the same?
Flux increases.
What does “phasor” represent in AC circuits?
A rotating vector representing magnitude and phase angle.
If inductance increases, what happens to XL at a fixed frequency?
XL increases.
What happens to current in a capacitor when the applied voltage changes faster?
Current increases.
In an RC circuit, what percentage of final voltage is reached after 1τ?
63%
What is the unit of magnetic flux?
Weber (Wb)
Convert 3 + j4 to magnitude.
5
Calculate XL for L = 0.05 H at 50 Hz.
(XL = 2πfL)
15.7 Ω
Calculate XC for C = 5 µF at 60 Hz.
(XC = 1 / (2πfC))
530.5 Ω
Find τ for R = 3 kΩ, C = 4.7 µF.
0.0141 s (14.1 ms)
A coil has N = 40 turns. The magnetic flux changes by 0.1 Wb in 0.25 seconds.
(E = –N ΔΦ/Δt)
A: –16 V
What is the phase relationship in a purely resistive AC circuit?
Voltage and current are in phase.
What stores energy in an inductor?
Magnetic field.
What happens to XC when capacitance increases?
XC decreases.
At resonance, total impedance equals what value?
R (only resistance remains)
What two things are required for electromagnetic induction to occur? induction?
A conductor and a changing magnetic field.
Find RMS value of a 28 V peak-to-peak AC waveform.
(Vrms = Vp / √2)
9.9 V
Current through an inductor is 1.5 A, and XL = 22 Ω.
Find voltage.
33 V
A capacitor with XC = 150 Ω has V = 30 V across it.
Find current.
0.2 A
Given R = 60 Ω, XL = 40 Ω, XC = 20 Ω, find total impedance:
Z = 63. 25 Ohms
A conductor of length 0.25 m moves at 2 m/s perpendicular to a 0.4 T magnetic field.
Find induced EMF.
E = BLv
0.2 V
Convert impedance Z = 8 – j6 to magnitude.
10 Ω
Find inductive reactance for L = 120 mH at 100 Hz.
75.4 Ω
Find XC for C = 2.2 µF at 1 kHz.
72.3 Ω
Find resonance frequency for L = 80 mH, C = 5 µF.
(fr = 1 / (2 Pi √(LC)))
251.8 Hz