Question

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A transformer has the voltages 25 V_pri and 140 V_sec. A current 3.5 mA is flowing in the primary. What is the current flowing in the secondary? (Assume 100 percent efficiency.) Submit Answer Save Progress Practice Another Version A machine in the factory needs 31V to operate. The power in the factory is different from that, so a transformer is needed. If the secondary to primary turns ratio {N_sec/N_pri) of the transformer is 0.0675, What is the voltage of the electrical power system in the factory? What would the voltage output be if the transformer were "accidentally" connected backward? An air-filled coil has 180 turns. The diameter of coil is 120 cm and the length is 88 cm. Find the inductance of the coil.

Answer 1

(11) The current flowing in the secondary which is given as :

using a formula, we have

I_S = I_P (V_S / V_P) = (3.5 mA) [(140 V) / (25 V)]

I_S = 19.6 mA

(12) A machine in the factory needs 31 V to operate.

a. The voltage of the electrical power system in the factory will be given as :

using a formula, we have

V_S = V_P (N_S / N_P)

(31 V) = V_P (0.0675)

V_P = (31 V) / (0.0675)

V_P = 459.2 V

(13) The inducatnce of the coil which will be given as :

using a formula, we have

L = _{$\mu$ 0} n² L A

where, A = area of the coil = $\pi$ r²

L = (4 $\pi$ x 10^-7 mT/A) (180)² (0.88 m) [(3.14) (0.6 m)²]

L = 404808.3 x 10^-7 H

L = 40.5 x 10^-2 H

L = 40.5 mH

(14) Given that :

inductance, L = 0.018 H

number of turns, n = 3100

diameter of cylinder, D = 2.6 cm

radius of cylinder, r = 1.3 cm = 0.013 m

a. It's length will be given as :

L = _{$\mu$ 0} n² L A

(0.018 H) = (4 $\pi$ x 10^-7 mT/A) (3100)² L [(3.14) (0.013 m)²]

(0.018 H) = (64051.5 x 10^-7 m³ T/A) L

L = (0.018 H) / (64051.5 x 10^-7 m³ T/A)

L = 2.81 m

convert m into cm :

L = 281 cm