Figure 6.20 shows a metal rod PQ resting on the smooth rails ABand positioned between the poles of a permanent magnet. The rails,the rod, and the magnetic field are in three mutual perpendiculardirections. A galvanometer G connects the rails through a switch K.Length of the rod = 15 cm, B = 0.50 T, resistance of the closed loopcontaining the rod = 9.0 mW. Assume the field to be uniform. (a) Suppose K is open and the rod is moved with a speed of 12 cm s–1in the direction shown. Give the polarity and magnitude of theinduced emf. (b) Is there an excess charge built up at the ends of the rods whenK is open? What if K is closed? (c) With K open and the rod moving uniformly, there is no netforce on the electrons in the rod PQ even though they do experience magnetic force due to the motion of the rod. Explain. (d) What is the retarding force on the rod when K is closed? (e) How much power is required (by an external agent) to keepthe rod moving at the same speed (=12cm s–1) when K is closed?How much power is required when K is open? (f ) How much power is dissipated as heat in the closed circuit?What is the source of this power? (g) What is the induced emf in the moving rod if the magnetic fieldis parallel to the rails instead of being perpendicular?

Figure 6.20 shows a metal rod PQ resting on the smooth rails ABand pos

1.	Figure 6.20 shows a metal rod PQ resting on the smooth rails ABand positioned between the poles of a permanent magnet. The rails,the rod, and the magnetic field are in three mutual perpendiculardirections. A galvanometer G connects the rails through a switch K.Length of the rod = 15 cm, B = 0.50 T, resistance of the closed loopcontaining the rod = 9.0 mW. Assume the field to be uniform. (a) Suppose K is open and the rod is moved with a speed of 12 cm s–1in the direction shown. Give the polarity and magnitude of theinduced emf. (b) Is there an excess charge built up at the ends of the rods whenK is open? What if K is closed? (c) With K open and the rod moving uniformly, there is no netforce on the electrons in the rod PQ even though they do experience magnetic force due to the motion of the rod. Explain. (d) What is the retarding force on the rod when K is closed? (e) How much power is required (by an external agent) to keepthe rod moving at the same speed (=12cm s–1) when K is closed?How much power is required when K is open? (f ) How much power is dissipated as heat in the closed circuit?What is the source of this power? (g) What is the induced emf in the moving rod if the magnetic fieldis parallel to the rails instead of being perpendicular?
Answer» Figure 6.20 shows a metal rod PQ resting on the smooth rails ABand positioned between the poles of a permanent magnet. The rails,the rod, and the magnetic field are in three mutual perpendiculardirections. A galvanometer G connects the rails through a switch K.Length of the rod = 15 cm, B = 0.50 T, resistance of the closed loopcontaining the rod = 9.0 mW. Assume the field to be uniform. (a) Suppose K is open and the rod is moved with a speed of 12 cm s–1in the direction shown. Give the polarity and magnitude of theinduced emf. (b) Is there an excess charge built up at the ends of the rods whenK is open? What if K is closed? (c) With K open and the rod moving uniformly, there is no netforce on the electrons in the rod PQ even though they do experience magnetic force due to the motion of the rod. Explain. (d) What is the retarding force on the rod when K is closed? (e) How much power is required (by an external agent) to keepthe rod moving at the same speed (=12cm s–1) when K is closed?How much power is required when K is open? (f ) How much power is dissipated as heat in the closed circuit?What is the source of this power? (g) What is the induced emf in the moving rod if the magnetic fieldis parallel to the rails instead of being perpendicular?

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