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Physics 42L – Spring 2008 Test 2 Notes Alex Beutel March 22, 2008 Chapter 25 - Electric Current and Direct-Current Circuits ∆Q = qnAvd ∆t V = IR L R=ρ A V2 P = IV = I 2 R = R Series: Req = R1 + R2 + R3 + · · · 1 1 1 1 Parallel: = + + + ··· Req R1 R2 R3 I= (1) (2) (3) (4) (5) (6) Capacitors τ = RC W = QV = CV 1 U = QV 2 2 (7) (8) (9) Time Constant is the time it takes for the charge to decrease by e−1 . Chapter 26 - Magnetic Field F = qv × B F = IL × B Magnetic moment µ = N IAˆ n Torque τ = µ × B U = −µB cos θ = −µ · B (10) (11) (12) (13) (14) 1 Chapter 27 - Sources of Magnetic Field µ0 qv × r ˆ 4π r2 µ0 = 4π × 10−7 B= Biot-Savart Law: dB = Magnetic field inside a solenoid: Bx = µ0 nI Gauss’s Law for Magnetism φm,net = s (15) (16) µ0 Idl × r ˆ 2 4π r (17) (18) Bn dA = 0 (19) Ampere’s Law Bt dl = C C B · dl = µ0 IC (20) • Paramagnetic materials do not interact strongly with external magnetic fields. Dipoles align somewhat but little increase in B. • Ferromagnetic materials are materials in which nearby molecules cause each other to align. As a result, a weak magnetic field can cause the alignment of all dipoles and creates a much larger magnetic field. Some are permanently aligned (permanent magnets). • “Diamagnetism arises from the orbital magnetic dipole moments induced by an applied magnetic field. These magnetic moments are opposite the direction of the applied magnetic filed, thereby decreasing the field.” All materials usually do this somewhat but are masked by ferromagnetism and paramagnetism. “Diamagnetism is thus observed only in materials whose molecules have no permanent magnetic moments.” See pages 874 to 885 Chapter 28 - Magnetic Induction φm = S B · ndA = ˆ S Bn dA d dt B · ndA ˆ s (21) (22) (23) (24) ε=V =− dφm = dt ε = −Blv Enc · dl = − C 2 Inductance φm = LI φm L= = µ0 n2 Al I dI ∆V = −L dt 12 Um = LI 2 Magnetic Energy Density um = B2 2µ0 (29) (25) (26) (27) (28) 3 

Document Info

Posted By:

Alex Beutel

Date:

Sunday, March 23, 2008

School:

Duke University

Class:

Physics 42L

Tags:

• Review Sheet
• Formula Sheet
• Biot-Savart
• Maxwell
• Induction
• Amperes Law
• Electromagnetism
• Physics

About this Document

Review for Dr. Brown's second test from Physics 42. Includes Ampere's Law, Faraday's Law, Biot-Savart Law, and other electromagnetism concepts