question_answer 47)

  Choose the incorrect statement. (a) Fleming's right hand rule is a simple rule to know the direction of induced current. (b) The right hand thumb rule is used to find the direction of magnetic fields due to current carrying conductors. (c) The difference between the direct and alternating currents is that the direct current always flows in one direction, where as the alternating current reverses its direction periodically. (d) In India, the AC changes direction after every second.

Answer:

                  (d) (a)  According to Fleming's right hand rule, if the direction of magnetic field and the direction of motion of conductor are given then we can find the direction of the induced current. So option (a) is correct. (b) In the right-hand thumb rule, we find the direction of magnetic field due to a straight current-carrying conductor. Thus option (b) is correct. (c) The direction and magnitude of AC changes periodically where as in case of DC these remains constant. So option (c) is also correct. (d) The frequency of 'AC' in India is 50 cycle/s. Therefore, time period of AC is 1/50 s. But AC changes its direction after every half time period, f.e., 1/(2x50) i.e., 1/100 s, Thus in India, the AC changes direction after every 1/100 s. Hence option (d) is incorrect.