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 5 of 6.
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.
Sharmila said:
9 years ago
150mw is wrong answer.
Because the given current is in maximum value, how you can multiple with root 2?
The formula is v (r.m.s) = [v(max.)/root 2]. So,the answer is 75mw.
Because the given current is in maximum value, how you can multiple with root 2?
The formula is v (r.m.s) = [v(max.)/root 2]. So,the answer is 75mw.
Supriyo said:
9 years ago
I too think 75mw is the correct answer.
Pratik suhas gajengi said:
9 years ago
You are right @R N Trimukhe.
Ravi ranjan said:
8 years ago
P=i2r bit here I is the RMS and irms =I'm/√2 now apply 25ma square * 120 * 2 = 150mw.
Rishipal said:
8 years ago
D is correct because maximum current is given it is not RMS current so, it changes in RMS current.
RMS current=maximum current/root2. Then power = i2r.
RMS current=maximum current/root2. Then power = i2r.
Rabindra Singh said:
8 years ago
150mA is the correct answer.
Given current is the rms value, and the rating must be decided on maximum current.
Imax = Irms * sqrt2 = 25mA * sqrt2 = 0.0353,
Hence rating =(Imax)^2 *120 = 150mW.
Given current is the rms value, and the rating must be decided on maximum current.
Imax = Irms * sqrt2 = 25mA * sqrt2 = 0.0353,
Hence rating =(Imax)^2 *120 = 150mW.
S.Mohamed said:
8 years ago
Thanks @Pranav.
Yashmendr Tiwari said:
8 years ago
@All.
The concept of max and rms fundamental is not right bz max current already given
then why you are calculate Imax = Irms * sqrt2 = 25mA * sqrt2 = 0.0353?
Please explain me.
The concept of max and rms fundamental is not right bz max current already given
then why you are calculate Imax = Irms * sqrt2 = 25mA * sqrt2 = 0.0353?
Please explain me.
Rojohn Ogalinola said:
7 years ago
Use a resistor rated for at least 2 times the required power dissipation.
Thus,
P=(25mA)^2 x 2(120ohm) = 150mW.
Thus,
P=(25mA)^2 x 2(120ohm) = 150mW.
(1)
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