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Transcript
Exam 4, Thursday, August 9, 2012 PH204 For Dr. Harold Williams Your Name: 1) Worth 8 points. 25.2 second half of Induced Current in a Circuit. A metal truck is driving East at 80 km/hr in a region where the earth’s magnetic field is 4.5 × 10-5T, north. a) what is the potential difference between the top and the bottom of the truck. b) Will the top be positive or negative relative to the bottom. 2) Worth 15 points. 24.4 and 25.3 Magnetic Flux: A solenoid 50 meters long and a diameter of 4 meters has 10,000 turns with a 2 A current is surrounded by a loop that is 5 km in diameter centered perpendicular to the solenoid. a) What is the magnetic flux in the loop? b) The loop is rotated 30 degrees. What is the magnetic flux now? c) 25.4 Faraday’s Law. The loop is rotated the 30 degrees in 5 minutes. This is some sort of science fiction movie device. What is the voltage induced in the 5 km loop by the 30 degree rotation in 5 minutes. 3) Worth 3 points. 25.5 Induced Fields and EM Waves. A an electromagnetic wave of frequency f and wavelength λ travels with a speed in a vacuum in term of the permittivity and permeability constants from our expression for electric and magnetic fields is what? 4) Worth 8 points. 25.6 Properties of Electromagnetic Waves. If the maximum leakage radiation from a microwave oven is 5.0 mW/m2 . What would be the maximum leakage amplitude of the electric fields? What would be the maximum leakage amplitude of the magnetic field? 5) Worth 8 points. 25.6 Properties of Electromagnetic Waves (polarization). Given unpolarized light and perfect polarizers, after the first polaroid filter what is the intensity of light? If the second polarizer is at a 30 degree angle with respect to the axis of the first polaroid filter what is the intensity after the second polaroid filter? The third polaroid filter is oriented such that without the second polaroid filter the angle is 90 degrees and no intensity gets through with the second filter removed from beyond the third filter. How much gets beyond the third polaroid filter with all three polaroid filters in and the orientation as stated? We saw this demonstrated in class! This is actually a two state quantum mechanical system with the wave function regenerated being demonstrated! This is actually deep physics! Draw a diagram showing your answer in terms of I coming into the first polaroid filter unpolarized and then after the first filter, then the second filter, and then the after the third filter. Don’t panic just do it! 6) Worth 8 points. 25.7 The Photon Model of EM Waves. What is the energy in joules and in electron volts of a single photon in the ultraviolet with a wavelength of 400nm? This is two questions! 7) Worth 8 points. 25.8 The EM Spectrum. The spectrum of an incandescent light has a wavelength peak of 1000nm, what is the temperature of the filament if it is a perfect blackbody radiator? At this temperature how much energy/area in Joules/ m2 comes off of the filament? 8) Worth 10 points. 26.2 AC Electricity and Transformers What is the ratio of the primary to the secondary windings (turns) for each of the three transformers in this diagram. a) Step-up transformer between the power plant and the high-voltage transmission lines? b) Step-down transformer (substation) between the high-voltage transmission lines and after the substation? c) Step-down transformer from after substation voltage to your house at 120 volts? 9) Worth 10 points. 26.4 Biological Effects and Electrical Safety If you place both hands on an electrified hot wire and it flows through to your feet both on the ground what is your resistance using the numbers above? Draw the resistance circuit, label it and calculate! If you place only one hand on the electrified hot wire and stand on one leg what is your equivalent resistance? Draw the resistance circuit, label it and calculate! If you foolish try to craw under a electrified hot wire on all fours, arms and legs, and your for head touches the hot wire with your feet and legs grounded what is your resistance using the number above and the added fact that you head has a resistance of 15 ohms? Draw the resistance circuit, label it and calculate! 10) Worth 10 points. 26.5 Capacitor Circuits. A 30 micro Farad capacitor is connected across and AC generator that produces a peak voltage of 12 volts and a peak current of 3 amps. What is the oscillation frequency? 11) Worth 8 points. 26.6 Inductors and Inductor Circuits. An RLC tuning circuit is used to bring in a signal with a wavelength of 21 centimeters. The inductor used in the circuit is 2mH. What is the value of the capacitor used in this tuning circuit? 21 centimeter radiation is used to study the density of atomic hydrogen in the cosmos. This is important in astronomy, big time! 12) Worth 4 points. Relativity. What are the two postulates or principles of special relativity?