1 / 22

Physics 2112 Unit 18

Physics 2112 Unit 18. Today’s Concepts: A) Induction B) RL Circuits. Where we are…. Just finished introducing magnetism. Will now apply magnetism to AC circuits. Remember Example 17.6 (solenoid)??. Changing current in outer loop Caused changing magnetic field in inner loop

alyson
Download Presentation

Physics 2112 Unit 18

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Physics 2112Unit 18 Today’s Concepts: A) Induction B) RL Circuits

  2. Where we are….. Just finished introducing magnetism Will now apply magnetism to AC circuits

  3. Remember Example 17.6 (solenoid)?? • Changing current in outer loop • Caused changing magnetic field in inner loop • Induced changing current in inner loop. What if you only had one loop? Would changing current in that induce anything?

  4. Self Inductance Depends only on the geometry of the coils Define: …caused by changes in the current in that same coil Voltage drop in a coil

  5. Example 18.1 (Inductance of Solenoid) What is the inductance of a solenoid? L

  6. Checkpoint 1 Two solenoids are made with the same cross sectional area and total number of turns. Inductor B is twice as long as inductor A Compare the inductance of the two solenoids A) LA= 4 LBB) LA= 2 LBC)LA=LBD)LA= (1/2) LBE)LA= (1/4) LB

  7. What the minus sign means….. A A DV < 0 VA > VB Increasing current Acts like a resistor IAB DVAB

  8. What the minus sign means….. A B DV > 0 VA < VB decreasing current Acts like a battery However you try to change the current through an inductor, the inductor resists that change. IAB DVAB

  9. What this really means: dI dt eL= -L emf induced across L tries to keep I constant. L currentI Inductors prevent discontinuous current changes! It’s like inertia! Units of inductance are Henrys (H) [Tm2/A]

  10. Time Constant I = 0 L R VBATT

  11. Example 18.2 (Current in Solenoid) A solenoid has 6500 loops in a length of 10cm and a radius of 6cm. It is attached to a 120W resistor and a 12V battery. What is the current through the resistor 0.01sec after the switch is closed? S R=100W L What is the current through the resistor 2.0 sec after the switch is closed? 12V= VBATT Would the current have been at 0.01sec if the inductor had an internal resistance of 20W?

  12. How to think about RL circuits: I = V/R L R VBATT At t >>L/R: At t = 0: VL= 0 VR=VBATT I=VBATT/R (L is like a short circuit) I= 0 VL=VBATT VR= 0 (Lis like a giant resistor) When no current is flowing initially: VL I = 0 L R I VBATT

  13. CheckPoint 2A I I In the circuit, the switch has been open for a long time, and the current is zero everywhere. At time t=0 the switch is closed. • What is the current I through the vertical resistor immediately after the switch is closed? (+ is in the direction of the arrow) • A)I = V/RB)I = V/2RC)I= 0 D)I =-V/2RE)I =-V/R

  14. CheckPoint 2B After a long time, the switch is opened, abruptly disconnecting the battery from the circuit. What is the current I through the vertical resistor immediately after the switch is opened? (+ is in the direction of the arrow) A)I=V/RB)I=V/2RC)I=0 D)I= -V/2RE)I= -V/R

  15. How to Think about RL Circuits Episode 2: VL I = 0 L R At t= 0: At t>>L/R: I=VBATT/R VR= IR VL=VR I= 0 VL= 0 VR= 0 VBATT When steady current is flowing initially: L R R I=V/R

  16. Why is there Exponential Behavior? + - dI dt VL V = IR + V = L - I L R where

  17. What are Inductors and Capacitors Good For? ” Can you have capacitors and inductors in the same circuit? “why inductors are important as opposed to capacitors. why use one instead of the other?” Inside your i-clicker

  18. Quick comment… I L R Did we mess up? VBATT VL Lecture: Prelecture: No: The resistance is simply twice as big in one case.

  19. CheckPoint 3A After long time at 0, moved to 1 After long time at 0, moved to 2 After switch moved, which case has larger time constant? A) Case 1 B) Case 2 C) The same

  20. CheckPoint3B After long time at 0, moved to 1 After long time at 0, moved to 2 Immediately after switch moved, in which case is the voltage across the inductor larger? A) Case 1 B) Case 2 C) The same

  21. CheckPoint 3C After long time at 0, moved to 1 After long time at 0, moved to 2 After switch moved for finite time, in which case is the current through the inductor larger? A) Case 1 B) Case 2 C) The same

  22. Example 18.3 (3R and L circuit) R1 R2 The switch in the circuit shown has been open for a long time. At t= 0, the switch is closed. V L R3 What is dIL/dt, the time rate of change of the current through the inductor immediately after switch is closed? • Conceptual Analysis • Once switch is closed, currents will flow through this 2-loop circuit. • KVR and KCR can be used to determine currents as a function of time. • Strategic Analysis • Determine currents immediately after switch is closed. • Determine voltage across inductor immediately after switch is closed. • Determine dIL/dt immediately after switch is closed.

More Related