Clutch Prep is now a part of Pearson
Ch 32: Alternating CurrentWorksheetSee all chapters
All Chapters
Ch 01: Intro to Physics; Units
Ch 02: 1D Motion / Kinematics
Ch 03: Vectors
Ch 04: 2D Kinematics
Ch 05: Projectile Motion
Ch 06: Intro to Forces (Dynamics)
Ch 07: Friction, Inclines, Systems
Ch 08: Centripetal Forces & Gravitation
Ch 09: Work & Energy
Ch 10: Conservation of Energy
Ch 11: Momentum & Impulse
Ch 12: Rotational Kinematics
Ch 13: Rotational Inertia & Energy
Ch 14: Torque & Rotational Dynamics
Ch 15: Rotational Equilibrium
Ch 16: Angular Momentum
Ch 17: Periodic Motion
Ch 19: Waves & Sound
Ch 20: Fluid Mechanics
Ch 21: Heat and Temperature
Ch 22: Kinetic Theory of Ideal Gases
Ch 23: The First Law of Thermodynamics
Ch 24: The Second Law of Thermodynamics
Ch 25: Electric Force & Field; Gauss' Law
Ch 26: Electric Potential
Ch 27: Capacitors & Dielectrics
Ch 28: Resistors & DC Circuits
Ch 29: Magnetic Fields and Forces
Ch 30: Sources of Magnetic Field
Ch 31: Induction and Inductance
Ch 32: Alternating Current
Ch 33: Electromagnetic Waves
Ch 34: Geometric Optics
Ch 35: Wave Optics
Ch 37: Special Relativity
Ch 38: Particle-Wave Duality
Ch 39: Atomic Structure
Ch 40: Nuclear Physics
Ch 41: Quantum Mechanics
Sections
Phasors for Capacitors
Phasors for Resistors
Resonance in Series LRC Circuits
Phasors
Impedance in AC Circuits
Alternating Voltages and Currents
Inductors in AC Circuits
Capacitors in AC Circuits
Power in AC Circuits
Resistors in AC Circuits
Series LRC Circuits
RMS Current and Voltage
Phasors for Inductors
Learn

Concept #1: Phasors for Inductors

Transcript

Hey guys, in this video we're going to talk about phasors and how they apply to the voltages in the currents through inductors. Alright, let's get to it. Remember guys that there are two functions that are very important regarding inductors in AC circuits, the current through an inductor and the voltage across an inductor at any time T. These functions are just given here and remember that they both occur at a different angle. The current occurs at an angle of omega T and the voltage occurs at some different angle theta prime which is omega T plus Pi over 2. Because both functions occur at different angles, they are said to be out of phase. The current actually lags the voltage in this case or you could say the voltage leads the current and what this means is readily apparent on phasor diagrams. In the first diagram I plot the current at its angle omega T. In the second diagram I plot the voltage at its angle omega T plus Pi over 2, plus that 90 degrees. Combining these two, we have the voltage ahead of the current by 90 degrees. It's very very important to remember that the voltage across an inductor leads the current, this is opposite to capacitors in AC circuits where the voltage lags the current. They're opposites, the voltage leads the current for inductors, the voltage of lags the current for capacitors.

Let's do a quick example about this. An AC source is connected to an inductor. At a particular instant in time, the current in the circuit is negative and increasing in magnitude. Draw the phasors for the voltage and the current that correspond to this instant in time. So here is my phasor diagram, remember what does it take for a phasor to be negative? It has to be on the left side of the graph because its horizontal component has to be negative. What does it take for it to be increasing in magnitude? It has to be moving towards the horizontal axis since it rotates counter-clockwise it has to be in the second quadrant, this has to be here so that it's negative and since it's rotating counterclockwise it's moving towards the horizontal axis so it's negative and increasing in magnitude. This is for the current. Remember that the current across, sorry, the current through an inductor lags the voltage. If you look at all the above in the green box, the voltage leads the current by 90 degrees so I would need to draw another phasor 90 degrees ahead and that would be the voltage across the inductor and that is our phasor diagram for an inductor in an AC circuit. Alright guys, this wraps up our discussion on phasors and how they pertain to inductors in AC circuits. Thanks for watching.

Practice: An AC source operates at a maximum voltage of 75 V and is connected to a 0.4 H inductor. If the current across the inductor is i(t) = iMAX cos[(450 s −1)t], 

a) What is iMAX? 

b) Draw the phasors for voltage across the inductor and current in the circuit at t = 4.2 ms. Assume that the current phasor begins at 0°.

Previous SectionRMS Current and Voltage