## PH 142 FALL 2014. WRITTEN HOMEWORK ASSIGNMENT #7 Problem 1. (10 Points). An electron with velocity of 50 ? ? ?̂ + 30 ? ? ?̂ and is located in the z plane at x=-2.5 m, y = 3 m. Find the magnetic field in the z=0 plane at x=-1m, y = 1m Answer 1.48 × 10−25? ?̂ Problem 2 (10 points) A long wire carrying current 0.1 A has the shape shown in the figure below. Find the magnetic field at point B Answer 4.81×10-7 T Problem 3. (10 points). Three infinitely long parallel wires are at the corner s of a square of side a as shown in the figure below. Each wire carries equal current I=1 Amp. Current 1 points into the page, and out to the page at 2 and 3. What is the magnitude of magnetic field at point, P? Answer 3.16×10-7 T 20 cm 10 cm I = 0.1 A 10 cm B Problem 4. (10 points). The current density in a long cylindrical conductor of radius R=15 cm varies with distance from the axis of the cylinder according to the relation J(r) = (40 A/m3) r. Find the magnetic field at the following perpendicular distances from the wire’s central axis: (a) 7.0 cm, and (b) 25 cm. Answer (a) 8.2×10-8 T (b) 2.25×10-7 T Problem 5. (10 points). A current balance is constructed in the following way: A 20-cm-Iong section of wire is placed on top of the pan of an electronic balance used in a chemistry lab. Leads are clipped to it running into a power supply and through the supply to another segment of wire that is suspended directly above it, parallel with it. (See figure below.) The distance between the two wires is L = 2.0 cm. The power supply provides a current I running through the wires. When the power supply is switched on, the reading on the balance increases by 3.0 mg (1 mg = 10-6 kg). What is the current running through the wire? Answer 3.83 A

PH 142 FALL 2014. WRITTEN HOMEWORK ASSIGNMENT #7 Problem 1. … Read More...