Phy2005 Applied Physics II Spring 2016 Announcements: Test 2 Wednesday, March 23 2 practice tests posted on course Tests page Review session in class March 21 in class + 1 evening tba PH travel next week APS Spring meeting; Prof. Lee subs

Science news page Link to NYT video “Total Solar Eclipse Will End the Day Before It Begins”

Non-magnetic metal plate induced current in metal: Eddy current Last time: Eddy currents I There is an emf around any loop where flux is changing!

Last Time t x -A x0x0 T (period) x = Asin(2  ft) frequency: f = 1/T angular frequency:  = 2  f = 2  /T “repeat time” 0T x rms

Last time: Iron Core AC V NpNp NsNs V p /V s = N p /N s p=primary s=secondary

Hot Neutral GND

Power Transmission Gainesville has a population of 120,000. On average approximately 200 W/person of electric power is required. Let’s assume that GRU transmits power with 120 V. How much current should be carried in the power line? P t = 120,000 x 200 W = 24,000,000 W = 24 MW P = IV, I = P/V = 24,000,000/120 = 200,000 A However, if we deliver power with 500,000 V, I = 24,000,000/500,000 = 48 A Now Joule heating (I 2 R) due to wire resistance (R) is reduced By (48/200,000) 2 = 5.8 x 10 -8

From now on, when you see voltage or current in lower case, those indicate AC voltage or current. I: DC currenti: AC current V: DC voltagev: AC voltage

R V = V o R v = v o sin(2  ft) P = V 2 /R = I 2 R = IV t P = V o 2 /R: constant in timeP = (v o sin(2  t)) 2 /R: varying in time T = 1/f V, V 2

v2v2 t We need to take the average (mean) of the time dependent power over one cycle!! P = (v o sin(2  t)) 2 /R: varying in time = /R = v o 2 /2 So on average replace

Root Mean Square (rms) Root does not mean square! You have a variable x. Square, take average, and put square-root. Use rms values of v and i for AC to evaluate average power. = v rms 2 /R = i rms 2 R = i rms v rms

Ex 22-2 A sinusoidal AC voltage source with a 20 V amplitude and a 15 Hz frequency is applied across an electric heater with 10  resistance. (a) Write down a mathematical expression for the voltage. (b) What is the rms value of the voltage source? (c) How much power is dissipated in this heater? (a) v = 20sin(94.2t) (b) v rms = V (c) = 20 W

Ex 22-3 A 75-W light bulb is operated on its rated 120 V/60 Hz power. Find the rms current drawn by the bulb. = i rms v rms i rms = 75/120 = A

ACADEMIC HONESTY Each student is expected to hold himself/herself to a high standard of academic honesty. Under the UF academic honesty policy. Violations of this policy will be dealt with severely. There will be no warnings or exceptions.UF academic honesty policy

Q1 A current is given by i = 2sin(40t) A. Find the peak current (A), the rms current (B), and the frequency. (A) (B) (C) 1. 2 A2.83 A 40 Hz 2. 4 A2.83 A 20 Hz 3. 2A1.41 A 6.37 Hz 4. 4 A1.41 A 12.7 Hz

R C L

Increase current through the coil from 0 to  i in  t. Loop area: A Length of coil: ℓ Winding density: n = N/ ℓ Causes flux change for each loop from  = 0 to  = AB where B =  o n  i V ind = - n ℓ  /  t = - n ℓ A(  o n)  i/  t = - n 2  o A ℓ (  i / t) L: self inductance geometrical quantity [L] = Henry For a long solenoid B =  o nI n: number of turns/m V ind = -L(  i/  t)

Joseph Henry American physicist Henry discovered the electromagnetic phenomenon of self-inductance. He also discovered mutual inductance independently of Michael Faraday, (1791–1867), though Faraday was the first to make the discovery and publish his results. [2][3][4] Henry developed the electromagnet into a practical device. He invented a precursor to the electric doorbell (specifically a bell that could be rung at a distance via an electric wire, 1831) [5] and electric relay (1835). [6] The SI unit of inductance, the henry, is named in his honor.electromagneticinductanceMichael Faraday [2][3][4]electromagnetdoorbell [5]relay [6] SIinductancehenry