In order to detect the movement of water in the ocean, oceanographers sometimes

Question

In order to detect the movement of water in the ocean, oceanographers sometimes rely on the motional emf generated by this movement of the water through the magnetic field of the Earth. Suppose that, at a place where the vertical magnetic field is 7.0x10^-5 T, two electrodes are immersed in the water separated by a distance of 200 m measured perpendicularly to the movement of the water. If a sensitive voltmeter connected to the electrodes indicates a potential difference of 7.0x10^-3 V, what is the speed of the water?

Explanation / Answer

Given: Magnetic field B = 7.0*10-5 T distance between the plates d = 200 m potential difference V = 7.0*10-3 V charge q = 1.6*10-19 C Electric field is the ratio of the potential difference to the distance between the plates. E = V/d     = ( 7.0*10-3 V)/( 200 m)     = 0.035 *10-3 V/m F = Bqv sin .........(1)    ( = 900) from the above equation 1 v = F/Bqsin .......(2)     (F = Eq) Hence equation 2 can be changed to v = E/Bsin    = (0.035*10-3 V/m)/(7.0*10-5 T)        = 0.245*102 m/s.     = 24.5 m/s. F = Bqv sin .........(1)    ( = 900) from the above equation 1 v = F/Bqsin .......(2)     (F = Eq) Hence equation 2 can be changed to v = E/Bsin    = (0.035*10-3 V/m)/(7.0*10-5 T)        = 0.245*102 m/s.     = 24.5 m/s.

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