大学物理甲下exercise2课件

1、Exercise LessonMagnetic field1. Calculating magnetic field (1) Use the Biot-Savart lawdBdBxdBExample 1: As shown in Fig. Find B at point P. R, I, and distance between O and P are known.Solution: rdByzxQSome distributions of magnetic field by currentA straight wire segmentLong straight current-carryi

2、ng wireThe center of a circular current loopThe center of a circular current arcInterior of a solenoidInterior of a toroid (2) Use superposition principle.Example 2: A infinite semi-cylindrical conducting shell with radius R carrying a current i. The current is uniform distributed. Find the magnetic

3、 field B at point P on the axisSolution:dBxyPR1R2IIRIR135Find the magnetic field at the center of the current circuit: (3) Use Amperes lawExample 3: A conducting plane with infinitely long and width is carrying a current, the current density per unit length is j. Find B. Ampere loopSolution:iBB (4)

4、The magnetic fields of the moving chargesExample 4: A charged rod with length b and charge density rotates about the axis through o and perpendicular to the paper with . The distance between o and end of the rod is a. Find B at point o. Solution:rdrFor circular moving2. The force and torque acted on

5、 a current-carrying wire by magnetic fieldThe force acted on a current-carrying wire by magnetic fieldExample 5: As shown in Fig., the square loop of wire with side 2a can rotate about axis oo . Find the net force and torque on the loop when it locate as shown respectively.bI1I2oo2aSolution:xy12F1r1

6、r212F1F2F1rF1xF2rF2xF2y12F1yThe torque acted on a current-loop by magnetic fieldExample 6: A insulating ring of radii R1and R2 carries a constant charge q which is uniform contributed. The ring is rotating with about the axis through the center and perpendicular the ring. The angle between the unifo

7、rm magnetic field B and the normal of the ring is . Find the torque on the ring by B.Solution:3. Inducted EMF (1) Motional EMFExample 7:As shown in Fig., the square loop of wire with side a is rotating about axis oo with . Find the induced EMF in the loop when it locate as shown .tdIooavBr1r2 The di

8、rection is clockwise from front view.Solution 1:Solution 2:tThe direction is clockwise from front view. (2) Induced EMFExample 8: B=0.50T,dB/dt=-0.10T/s, oabc is a square coil with side l=0.10m. Find (1) the induced electric field at point o, a, b, and c, (2)the induced EMF in the side oa, ab, bc and co. oabcSolution 1:clockwise oabc oabcESolution 2:Example 9: As shown in Fig. I(t)=I0e-t, a, b, v are all known. When t=0, the moving side is located at y=0. Find (t) and (t) at any time.oyI(t)abvySolution 1:Solution 2:When t1, 0, clockwise.When t1, 0, counterclockwise.Page 799 P