Question

Please help with BOTH of the following questions for a thumbs up! Thanks!

8. + -/1 points SerPSE 10 32.8.OP.021. My Notes + Ask Your Teach A step-down transformer is used for recharging the batteries of portable electronic devices. The turns ratio N/N, for a particular transformer used in a DVD player is 1:14. When used with 120-V (rms) household service, the transformer draws an rms current of 33.0 mA from the house outlet. (a) Find the rms output voltage (in V) of the transformer. (b) Find the power in W) delivered to the DVD player. w (c) What If? What would be the current (in ma) drawn from the house outlet if the transformer had an efficiency of 92.0%, but the power delivered to the Blu-ray player remains the same? ma

Answer 1

(8) Turn ratio of step-down transformer, N2 / N1 = 1/14

Primary voltage, V1 = 120 V

Primary current, I1 = 33.0 mA = 0.033 A

(a) Secondary voltage of the transformer, V2 = V1*(N2 / N1)

= 120 * (1/14) = 8.57 V

So, rms output voltage of the transformer = V2 = 8.57 V (Answer)

(b) Power delivered to the CD player, P = V1*I1 = V2*I2 = 120*0.033 W = 3.96 W (Answer)

(c) Secondary side current of the transformer in ideal case, I2 = I1 *(N1 / N2)

= 0.033*(14 / 1)

= 0.462 A

= 462 mA

Efficiency of the transformer = 92.0 %

Power of the CD player remains the same. Also the source voltage will be the same. Only the drawn current will vary.

Therefore, current drawn by the source in this case, I1' = I1 / 0.92 = 33 / 0.92 = 36.0 mA (Answer)

(10) Step-up transformer. Means, number of turns on the secondary side will be more than the number of turns in the primary.

N1 = No. of turns on the primary = 74

N2 = No. of turns on the secondary = ?

Primary voltage, V1 = 110 V

Secondary voltage, V2 = 2200 V

For an ideal transformer,

V1 / V2 = N1 / N2

=> N2 = N1 *(V2 / V1) = 74 *(2200 / 110) = 1480 (Answer)

(b) Secondary current, I2 = 1.10 A

So, primary current, I1 = I2*(N2 / N1) = 1.10*(1480 / 74) = 22.0 A (Answer)

(c) Secondary current, I2' = 1.20 A

So, primary current in the ideal case, I1' = I2'*(N2 / N1) = 1.20*(1480 / 74) = 24.0 A

Transformer efficiency = 93.0 %

So, the actual primary current = I1' / 0.93 = 24.0 / 0.93 = 25.8 A (Answer)