Consider a horizontal metal rod of length w=18 cm and mass m=0.07 kg with metal

Question

Consider a horizontal metal rod of length w=18 cm and mass m=0.07 kg with metal loops at both ends that go around two vertical metal poles (see figure). The rod is in electrical contact with the poles and can slide freely up and down. The poles are connected to a battery and current I=6 A flows through the rod. There is a uniform magnetic field B in the region of the rod that is large enough to neglect the magnetic field from the 6 A current and oriented to have the maximum effect. The rod floats at rest h=3 cm above the table. (a) What is the magnetic field in the region of the rod? (Assume +x is to the right, +y is up, and +z is out of the page.) (b) In which direction is the magnetic force on the bar? (c) If the conventional current in the bar were to the left (opposite of the picture), would the bar still float? Explain.

Explanation / Answer

Force on wire due to field = Gravitational force on the wire BIL = Mg --->> B * 6 * 0.18 = 0.07 * 9.8 B = 0.635 T [Cant predict the direction as the figure is not given, But B will be such that the force due to it will be in upward direction]. Magnetic force will be in upward direction. No, the bar wont float, the force of gravity and magnetic force will be in same direction.

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