Question

Review Con: Part A An incandescent light bulb uses a coiled filament of tungsten that is 580 mm long with a diameter of 46.0 um. At 20.0°C tungsten has a resistivity of 5.25 x 1012.m. Its temperature coefficient of resistivity is 0.0045 (Cº) , and this remains accurate even at high temperatures. The temperature of the filament increases linearly with current, from 20°C when no current flows to 2520°C at 1.00 A of current What is the resistance of the light bulb at 20°C? Express your answer with the appropriate units. LH MÃ 6 * Ea ? R(20°C) = Value Units Submit Previous Answers Request Answer X Incorrect; Try Again; 4 attempts remaining Part B What is the current through the light bulb when the potential difference across its terminals is 120 V? (Hint: First determine the temperature as a function of the cu then use this to determine the resistance as a function of the current. Substitute this result into the equation V=IR and solve for the current I.) Express your answer to two significant figures and include the appropriate units. R ? O Å I = Value O O Units Submit Request Answer

Answer 1

Part A R (20) = pe R. (20) = (5-25 X10%) 580x103 x 4 (46X106)2) E 18.3220 Part B A TEKI (where k is a constant) where at T = 26206 I=14 2520 = K (1) so = 25 20 C/A R (2520) = Ro[1+&OT] ST = 25000 R (2520) = 18.322 [i+ 0.0045 x 2500] R (2520) = 224.4445 n V = 1x224.44450 A A V=DR - IR=120 IR=120 I'Ro 11+ (7020)] = 120 T & 18.322 [it 0.0045T - 0.09] = 120° 2520 T1 0.0015 T+ 0.91] = 16504.74 0.0045T²+0.91T - 16504.74 = 0 so T= 1816.6354 °C so I = 1816.6859 - 0.721 A 3 current i = 0.721 A 2520

l'arte p (1816.6254") = 18.322 11+ 0.045 (1216.6954-20)] so Rat potential 126 is. R = 166.457 ~ Part Inangy dissipale by light bulb is Inien = I2Rt & = (0-721) ² x 166.457860 & F 5191.27 so -5.191 kJ