A wire of mass 40 g slides without friction on two horizontal conducting rails s

Question

A wire of mass 40 g slides without friction on two horizontal conducting rails spaced 0.8 m apart. A steady current of 100 A is in the circuit formed by the wire and the rails. A uniform magnetic field of 1.2 T, directed into the plane of the drawing, acts on it. (a) In which direction in Figure 19.44 will the wire accelerate? (b) What is the magnetic force on the wire? (c) How long must the rails be if the wire, starting from rest, is to reach a speed of 200 m/s? (d) If the magnetic field were directed out of the page, how would your answers differ? (e) What if the magnetic field were directed toward the top of the drawing?

Please explain!

Explanation / Answer

a) it will accelarate in the right direction - use using the right hand rule put the direction-finger in the direction of current(I) and middile fingure in the direction of he magnetic field(B) then your thumb will be in the direction of magnetic force on the wire, and the accelaration of the bar would be in the same direction as the force which is right side.

b)magnetic force F = IBL = 100*1.2*0.8 = 96 N

c) Force on bar F= 96 N from (b) and given mass of bar M = 40g=0.04kg

accelaration of bar = F/M = 2400m/s^2 to reach the velocity of 200m/s time t = v/a = 200/2400 = 0.0833 seconds

d) if the directin of magnetic field changes then direction of bar would also changes to left side.

e) if the magnetic field is parallel to the page then there is no motion for the bar since there will be no magnetic force on the bar F = I (l B sin0) = 0

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