electromagnetic induction

2009-02-16 8:21 pm

The frictionless rail is placed in a uniform magnetic field pointing into the paper. A smooth iron rod AB is placed on the rail such that a rectangular loop ABCD is formed as shown in the figure. The iron rod is given a sudden push towards the right with an initial velocity v. A current is induced in the loop ABCD. The rod stops after some time.

http://img14.imageshack.us/img14/8923/phy1ee1.png

(i)What is the direction of the induced current ?

(ii) Explain why the rod slows down and comes to a stop.

(iii) What is the kinetic energy of the iron rod converted to ?

(iv) The initial speed of the iron rod is 0.2m/s and the specific heat capacity of iron is 480 J / kg C. Find the rise in temperature of the iron rod. Neglect any forms of energy loss other than that in (iii).

回答 (1)

Prof. Physics

2009-02-16 9:35 pm

✔ 最佳答案

i. By Fleming's right hand rule, the induced current flows in a clockwise direction in the loop ABCD.

ii. After the induced current flows in the loop, by Fleming's left hand rule, the rod AB will experience a magnetic force directed to the left, which opposes the motion of the rod.

So to speak, the rod AB experiences a retarding force and hence it slows down and finally stops.

iii. The kinetic energy of the iron rod converts to the electrical energy in the current, then converts to the internal energy of the rod.

iv. Assume no energy is lost to the surrounding,

By the law of conservation of energy

K.E. loss by the rod = Gain in internal energy

1/2 mv^2 = mc△T

1/2 (0.2)^2 = 480△T

Temperature rise, △T = 4.17 X 10^-5 *C

參考: Physics king

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