Electrical Engineering - Energy and Power - Discussion

Hi friends:.

Here R=120 ohm.

I (max) =25 mA.

{I (max) means current will not go beyond 25mA}.

So power P=I*I*R= 25m*25m*120 = 75mW.

It means that power will not increase beyond 75mW.

And the word rating means that whatever device you are using will breakdown or may get burn. So in the question 75mW is necessory to keep resistor active (must not get burn). So 15mW is wrong. So 75mW rating resistor required. BUT BUT in market u'll not get exact same rating resistor. So you must go beyond the 75mW. And nearly rated resistor is 150 mW. So the correct option is (B) =150mW.

Because no one wants to go for higher rating, because cost increases, so option A and D are also wrong.

Hope you understood. Bye.

Answer should be 74mW not 150mW as V=IR and P=VI.

Answer should be 75mW. It should be verified.

p= i2r or p=vi so v=ir =25/1000 * 120=3v

p=vi =3*0.025 = 0.075= 75mv

OR

P=I2R =0.025Square *120 = 75mv

Yes pankaj is true.

Pankaj ahuja is correct.

p= 25*1.414*25*1.414*120*10*-3= 150mw

Vrms = Vm/1.414=25
its given in rms so convert vmax.

75mw is correct but rating is alwaya more, so 150mw which is nerest to 75mw according to option is correct.

@Pankaj ahuja is correct.

Sravanthi is correct.