Electrical Engineering - Energy and Power - Discussion
Discussion Forum : Energy and Power - General Questions (Q.No. 9)
9.
A 120 
resistor must carry a maximum current of 25 mA. Its rating should be at least
resistor must carry a maximum current of 25 mA. Its rating should be at leastDiscussion:
59 comments Page 2 of 6.
Sandy said:
1 decade ago
Current = 25 ma = 0. 025 a.
Voltage = ?
Resistor = 120 ohm.
I = v/r.
v = ir.
v = 0.025*120 = 3 v.
p = vi.
p = 3*0.025 = 0.075 w = 75 mw.
Voltage = ?
Resistor = 120 ohm.
I = v/r.
v = ir.
v = 0.025*120 = 3 v.
p = vi.
p = 3*0.025 = 0.075 w = 75 mw.
Stuti kushwaha said:
10 years ago
Irms = 25.
Im = (25*1.414)^2*12 = 150 mA.
Im = (25*1.414)^2*12 = 150 mA.
PRITAM said:
10 years ago
The answer should be 75 mw because which is not in option. Some of guys have said that it will be 150 mw. How if you really did then I think you must solved after seeing an option?
Rkn said:
10 years ago
How could 150mW be correct answer. It is clear from the question that for a power rating beyond 75mW the resistor's characteristics will be altered.
So the maximum rating is 75mW and among options only 15mW is less than this value. So the answer should be 15mW. Anyway a 20W rated doesn't burn out at this value.
So the maximum rating is 75mW and among options only 15mW is less than this value. So the answer should be 15mW. Anyway a 20W rated doesn't burn out at this value.
Ravi said:
10 years ago
Formula:
Irms = Im\root2 then Im = Ir*root2.
Im value is = 25 mA*root2 = 0.03536 A.
Then P = I*I*R = 0.03536*0.03536*120 = 150 mW.
Irms = Im\root2 then Im = Ir*root2.
Im value is = 25 mA*root2 = 0.03536 A.
Then P = I*I*R = 0.03536*0.03536*120 = 150 mW.
Prasad said:
10 years ago
Rating of resistor = 2VI.
OMVEER SINGH said:
10 years ago
Max. current always Taking in RMS Value. So we solve this query by Rms value Imax = Square root*Irms.
Then P = I*I*R.
= 25*1.414*25*1.414*120.
= 150 MW.
Then P = I*I*R.
= 25*1.414*25*1.414*120.
= 150 MW.
Ashish said:
10 years ago
How answer is 150?
Shyam said:
1 decade ago
Current should be in RMS value. So answer will be (75/2).
Hemant said:
9 years ago
Rated value means the device should operate that value. Here, 75mW is the right answer. We can't say the rated value is 150mW as per the formula.
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