lenz's law

Name: Grade & Section: Score: School: Teacher: Subject: General Physics 2 LAS Writer: JAN JEFFREY R. CAMINA Content Editor: Learning Topic: Lenz's Law; Quarter 4-Week 1 LAS 2 Learning Targets: Compare and contrast alternating current (AC) and direct current (DC). STEM_GP12EM-IVA-6 Reference(s): Wolfe, Gregg, Erika Gasper, John Stoke, Julie Kretchman, David Anderson, Nathan Czuba, Liza Puji, Irina Lyublinskaya, and Douglas Ingram. 2015. "Alternating Current versus Direct Current". Openstax. https://openstax.org/books/college-physics-ap-courses/pages/20-5-alternating- current-versus-direct-current Alternating Current (AC) vs. Direct Current (DC) Direct current (DC) is the flow of electric charge in only one direction. It is V, I (a) the steady state of a constant-voltage circuit. Most well-known applications, VDC however, use a time-varying voltage source. Alternating current (AC) is the flow IDC of electric charge that periodically reverses direction. If the source varies 0 periodically, particularly sinusoidally, the circuit is known as an alternating current circuit. Examples include the commercial and residential power that serves so many of our needs. Figure 1 shows graphs of voltage and current versus time for typical DC and AC power. The AC voltages and frequencies commonly used in V, I (b) homes and businesses vary around the world. Vo Figure 2 shows a schematic of a simple circuit with an AC voltage source. The voltage between the terminals fluctuates as shown, with the AC voltage given by: where V is the voltage at time t, Vo is the peak voltage, and f is the frequency in V = Vo sin (27 ft), -Vo - hertz. For this simple resistance circuit, I=V/R, and so the AC current is: Figure 1. (a) DC voltage and current are I = lo sin (2n ft) constant in time, once the current is established. (b) A graph of voltage and We are most often concerned with average power rather than its fluctuations that current versus time for 60-Hz AC power. 60W light bulb in your desk lamp has an average power consumption of 60 W, for The voltage and current are sinusoidal and example. As illustrated in Figure 3, the average power Pave is: are in phase for a simple resistance circuit. The frequencies and peak voltages of AC Pave = Irms Vrms, Irms = Vrms = Vo sources differ greatly. V2 V2 Pave = - To . Vo - 1 10 Vo: V2 V2 2 Example: V (a) What is the value of the peak voltage for 120-V AC power? (b) What is the peak +V. power consumption rate of a 60.0-W AC light bulb? For (a): - Vo Solving the equation Vrms= _ for the peak voltage Vo and substituting the known value for Vims gives: Vo=2-V2Vrms=1.414(120 V)= 170 V. This means that the AC voltage swings from 170 V to-170 V and back 60 times every second. An equivalent DC voltage is a constant 120 V. For (b) : Peak power is peak current times peak voltage. Thus, Figure 2. The potential difference between the terminals of an AC voltage Po= loVo= 2( loVo) = 2Pave. So the power swings from zero to 120 W on source fluctuates as shown. The hundred twenty times per second (twice each mathematical expression for V is given by V Po = 2(60.0 W) = 120 W. cycle), and the power averages 60 W. = Vosin2rift Average Activity: P power Given a transmission line having a line resistance of 5.000 sove for the following. Use the rubrics as your guide in presenting your solution (refer to attachment A.1 at the next page). (a) What current is needed to transmit 250 MW of power at 400 kV? (b) What is the power dissipated by the transmission lines if they have a resistance of 5.000? Figure 3. AC power as a function of time (c) What percentage of the power is lost in the transmission lines? Since the voltage and current are in phase here, their product is non-negative and fluctuates between zero and loVo- Average power is (1/2)loVo