The Strange World of Dr. Lentz W14D1

GOOD FRIENDS?? Faraday and Lentz

Calendar Thing MondayWednesdayFridaySaturday 14 Chapter 22 Gauss (Read rest of chapter) 16 (Read rest of chapter) 2 WebAssigns Chapter 22 Gauss 18QUIZ Chapter 22 Lentz & More 21 Chapter 23 Faraday 23QUIZ Chapter 23 Faraday HOLIDAY 28 Chapter 23 Faraday 30 Chapter 24 EM 2 Chapter 24 EM Optional Exam (22-24) 3 FINAL EXAM

Remember Flux? What is the magnetic flux through the rectangle? A) 0.2 Tm 2 B) 0.5 Tm 2 C) 1.2 Tm 2 D) 3.0 Tm 2 E) 4.2 Tm 2

Solenoid radius 2 cm. Ring radius 10 cm. B =.5 T inside solenoid. B≈0 outside the solenoid. What is the magnetic flux through the outer ring? A) 0 Tm 2 B) 6.3e–4 Tm 2 C) 6.3 Tm 2 D) 1.6e–2 Tm 2 E) 3.14e–2 Tm 2

From Faraday This - dB/dt is important NC

So, continuing The power supply is slowly turned up, increasing the current in the solenoid. While the current is increasing, what is the direction of inside the solenoid? A) = 0 B) To the right C) To the left D) Toward New York

Last Time - Maxwell Coulomb/Gauss Gauss – Magnetism Faraday’s Law Extended Ampere’s Law

A Parallel Universe Lentz’s Law

Induced Magnetic Fields always FIGHT to stop what you are trying to do! i.e... Murphy’s Law for Magnets Lenz’s Law

Example of Nasty Lenz The induced magnetic field opposes the field that does the inducing!

From Before.. as a reminder This - dB/dt is important

So, back to the question The power supply is slowly turned up, increasing the current in the solenoid. While the current is increasing, what is the direction of inside the solenoid? A) = 0 B) To the right C) To the left D) Toward New York

The power supply is slowly turned up, increasing the current in the solenoid. The initial B is show on the diagram. The current increases so B increases as well by dB in time dt. Effect is a field reduction caused by the induced current which must be opposing the original current (- sign). The net emf is reduced as is the current. (Ohm’s Law). The induced current opposes I. B The total emf is changed (reduced ) by this amount.

The power supply is slowly turned up, increasing the current in the solenoid. B The total emf is changed (reduced ) by this amount. What does Lentz tell us???

Remember the Pipe Demo Do you remember it? Can you explain it? Mini Activity on the Pipe  Whiteboard Presentation Aluminum Pipe SNSN

ACTIVITY #2 Let’s look at how a “transformer” might work.