Electronics - Resistance and Power - Discussion


With 1 mA of current, what wattage rating should a 470 ohm resistor have?

[A]. 1/4 watt
[B]. 1/2 watt
[C]. 1 watt
[D]. 2 watts

Answer: Option A


No answer description available for this question.

Manikanta said: (Apr 19, 2012)  
P=I^2R, So
P = 1*10^-6*470 = 0.00047W. How will come 1/4. Please explain?

Rathi said: (Apr 19, 2012)  
Yes you are right.
But we should take the wattage of the resistance greater than calculated value.
0.25(i.e 1/4) is greater than 0.00047W, So 1/4 is enough.
That means 1/4 watt is the right answer.

Note: If 1/8watt is given in option then 1/8 will be the correct answer.

Domy Dimal said: (Oct 22, 2014)  
0.25 w is greater than 0.00047w. Then how?

Theophillus said: (May 7, 2015)  
I don't understand how did you get 0.25 W there seriously.

Vasava said: (Aug 31, 2015)  
I can't understand how it come 0.25 watt?

Priyank Sharma said: (Jun 2, 2016)  
Why its answer is 0.25watt?

A.Sathish said: (Jun 29, 2016)  
0.00047w is correct, which is the nearest value.

Lewis said: (Aug 19, 2016)  
On our resistor wattage we have 1/8W, 1/4W, 1/2W, 1W,2W so when we rate we take the closest to 0.00047W which is the 0.25W. If there was the 0.125 W(1/8) resistor would be more suitable.

Fred Simz Jr said: (Feb 9, 2017)  
I can't understand how 0.25w came?

Please explain.

Vignesh said: (Apr 11, 2017)  
Here, the m value is 10^-3 then how to get the answer 1/4?

Soni said: (Sep 16, 2017)  
P= IV, P=I*I*R.

Engr Faizan Rais said: (Sep 28, 2018)  

So putting the values:
p = (40mA)^2*470
p = 0.751W
So, 0.751 w is nearer value to 1 w, the ans is 1 watt.

Gopal said: (Sep 17, 2019)  
I am not getting the solution. Please explain it.

Gopala said: (Sep 17, 2019)  
Explain how it come 1/4?

Rajesh said: (Oct 4, 2019)  
0.00047 less than 1/4 watt so least one is 1/4 watt is right answer.
1000mW = 1W, 0.250W is correct.

Thea said: (Apr 11, 2020)  
1/4 watts, 1/2 watts or 1 watts means the physical size of the resistor and not the technical measures.

1/4 watts means the resistor physical size is smaller. This usually uses in experiments or another device that handle a small amount of power.

And 1 watt means the physical size of the resistor is bigger and usually use in high power use to be not destroyed immediately by the current flowing.

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