EXAM 3 December 5, 1986 PS 208 If you need a constant not given here or do not understand a problem, please ask me about it. No notes, books, etc. may be used during this exam. 2 -19 g = 9.8 m/sec e = 1.6 x 10 C 9 2 2 1/ (4 pi epsilon ) = 9.0 x 10 N m / C 0 -31 The mass of the electron is 9.11 x 10 kg. 1. Show carefully that the field between two | | wires carrying current in opposite directions as ^ | | | | | | V in the diagram to the right is | | <---d---> mu I 0 1 1 B = ------- [ ---------- + ----------- ] 2 pi d/2 + x d/2 - x 2. The circuit shown on the right is a --- L=0.20 hen ---- | | | | rather primitive "low-pass" filter. For EMF R=50 ohm | | | | an EMF of 20 V, find the potential drop |___________________| across the 50 Ohm resistance if the input frequency is omega = 20/s and if the 1 input frequency is omega = 3000/s . In a 2 maximum of one sentence and one equation tell what would happen if equal EMF's of each frequency were applied simultaneously. 3. Show that the inductance per unit length of the wires in mu 0 d-a problem 1 is L/l = ---- ln ----- , pi a where a is the wire radius. Neglect the flux within the wires. 4. A metal ring of area A is placed in a constant, uniform field B in such a way that its area vector makes an angle theta to the lines of B. The loop now rotates about a diameter so that theta = omega*t. If the resistance of the coil is R, find the current through the coil as a function of time. The current-carrying coil experiences a torque in the magnetic field. How large is this torque?