Which of the following is (are) False? Circle it (them). (a) A step up transform

Question

Which of the following is (are) False? Circle it (them). (a) A step up transformer is a device that can be used to decrease the amplitude of an alternating voltage. (b) If an electric voltage is given by E(t) = E_max sin t then the resulting current can be written as E(t) = E_max sin (t -) (c) Two wires carry electric currents in the same direction. The result is the two wires will attract each other. (d) Two wires carry electric currents in the same direction. The result is the two wires will repel each other. (e) The Hall effect can be used to determine if the charge carriers in a material are negative or positive. The magnetic field through the conducting ring at the right changes according to the x x x x x x x x x x relation B(t) = 47t^4 T, where t is in seconds. The radius of the loop is 23.8 cm x x x x x x x x x x and the resistance is 23.6. Determine the current (magnitude and direction) x x x x x x x x x x in the loop at t = 2.6 seconds? (a) 1.00 times 10^A (b) 1.52 times 10^A. (c) 2.49 times 10^A. (d) 3.55 times 10^A. x x x x x x x x x x (e) 6.09 times 10^A. (f) ________ A. x x x x x x x x x x Direction: CCW or CW x x x x x x x A 12.8 m ohm resistor, 1.66 mu H inductor and switch are connected in series across an ideal R EMF source E = 35.0 V. How much energy is stored in the magnetic field of the L inductor when switch S is closed and the magnetic field becomes stable? In the previous problem, how long after switch S is closed until the magnetic field is stable? (a) 0.05 ms (b) 0.25 ms. (c) 0.38 ms. (d) 0.42 ms.

Explanation / Answer

28)(a) and (d) are found to be false

29)i=emf/resistance

emf induced=(dB/dt)A

=(47*4)(2.6^3)(22/7)(23.8^2)(10^-4)

=4117.6 volts

i(induced current)=4117.6/23.6=174.4 amperes

(resistance units were not mentioned)

ii)ccw

30)E=1/2*L*i^2

i=emf/R

E=591.6J (once the magnetic field is stabilised)

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