LECTURE 19 Pick up lecture notes Pick up lecture notes Practice test/review on Sunday, March 4 th at 11 am (note change of time), NSH 123 Practice Questions will be posted on the Web, under Exams Practice test/review on Sunday, March 4 th at 11 am (note change of time), NSH 123 Practice Questions will be posted on the Web, under Exams

Magnetic fields caused by currents Concept Test: After closing the switch in the above experiment, the current flows a.) from the switch towards the compass b.) from the compass towards the switch c.) not enough information to decide Concept Test: After closing the switch in the above experiment, the current flows a.) from the switch towards the compass b.) from the compass towards the switch c.) not enough information to decide N S N S B Earth

Concept Test : A battery establishes a steady current around the circuit below. A compass needle is placed successively at points P,Q, and R. The Relative deflection of the needle, in descending order,is Concept Test : A battery establishes a steady current around the circuit below. A compass needle is placed successively at points P,Q, and R. The Relative deflection of the needle, in descending order,is P Q R 1.P, Q, R 2.Q, R, P 3.R, Q, P 4.P, R, Q 5.Q, P, R

Concept Test : Two very long fixed wires cross each other perpendicularly (see figure). They do not touch, but are very close to each other, as shown. Indicate all the points where the net magnetic field is zero Concept Test : Two very long fixed wires cross each other perpendicularly (see figure). They do not touch, but are very close to each other, as shown. Indicate all the points where the net magnetic field is zero I I

Force between two parallel wires III Repulsive Attractive

Problem A rectangular loop is placed next to a straight wire as shown in the figure. What is the direction and the magnitude of the net magnetic force acting on the loop? Problem A rectangular loop is placed next to a straight wire as shown in the figure. What is the direction and the magnitude of the net magnetic force acting on the loop? d w l I I

Ampere’s Law Example: Infinitely long wire

Ampere’s Law: Applications Toroid with N turns: Calculate and sketch the magnetic field around the toroid as a function of the radial distance r from its center. B(r) r a b