What is the maximum safe current and voltage for a 140 ohms, 1/2 watt resistor?

In summary, This conversation is about calculating the maximum current and voltage that a 140 ohms, 1/2 watt resistor can handle without overheating. The formula P = V^2/R is used to calculate the maximum voltage of 8.366V, and the formula P = I^2*R is used to calculate the maximum current of 59.76 mA. The term electromotive force (EMF) is also discussed, which is equivalent to voltage. However, it is being phased out due to being a misnomer. It is important to recheck values to ensure they satisfy the equations.
  • #1
Bobzombie
2
0
have looked thought all my notes and books and can not find the formal on how to do this question. I'm slowly going out of my mind any help would be great

Calculate the maximum current a 140 ohms, 1/2 watt resistor can have flowing through it safely.
Enter answer: mA

Then the 2nd part of the question is

What is the maximum e.m.f. which may be applied to the resistor above without causing overheating?

Enter Part 2 answer: V
 
Physics news on Phys.org
  • #2
Do you know the relationship between ohms, amps, volts and watts? If so, using the formulas you can get it.
 
  • #3
re

P = I^2 * R

I = sqrt(P/R) = sqrt(0.5/140) = 59.7 mA
 
  • #4
emf? I have not encounter this question before :confused:
 
  • #5
I have a question almost 100% identical to this one...
I know the first part, but is part two simply E=IR ??

I just have never seen e.m.f. being used to refer to voltage... and can't find any help anywhere on it
 
  • #6
emf stands for electromotive force. Same thing as voltage.

In the first part it tells you what is the watt rating of the resistor. Power is determined by P = I^2 *R or P= V^2 / R or V=I*R.

If you have the value of the resistor and the watt rating you can easily figure out the answer.

PART 2: V or E is the variable to be found. Since we only have P and R let us use the relationship P = V^2 / R
0.5W = V^2/ 140 ohms

if the watt rating of a resistor is 0.5W that means the resistor will only be able to handle so much power until it burns out. So let us complete this problem.
sqroot(0.5W*140 ohms) = V or E
V or E = 8.366V

So if you apply 8.366V, you are on the border line of the max voltage the resistor can take.( in reality a resistor's watt rating is given a 10-20% margin I believe).
If you divide 8.366V by 140 ohms you get 59.76 mA which the maximum current the resistor can handle. How do you know this is the max current? well use P=V*I to check.
 
  • #7
thanks a lot for you help ^_^

I only asked if I should use E = IR because the first part is calculating current, and once you have that voltage is easy

just wish my textbook/teacher had told me that electromotive force is the same thing as voltage, haha
 
  • #8
True, you can use the current you calculated. But if you made a mistake in getting the current, the error would carry on.

Always recheck your values to see if they satisfy the equations.
 
  • #9
Maeode said:
thanks a lot for you help ^_^

I only asked if I should use E = IR because the first part is calculating current, and once you have that voltage is easy

just wish my textbook/teacher had told me that electromotive force is the same thing as voltage, haha

They're trying to phase out the term. Voltage isn't a force so EMF is a misnomer.
 

FAQ: What is the maximum safe current and voltage for a 140 ohms, 1/2 watt resistor?

What is the definition of maximum current?

The maximum current, also known as peak current, is the highest value of electric current that can flow through a circuit or device without damaging it.

How is maximum current calculated?

The maximum current is calculated by dividing the maximum voltage by the resistance of the circuit or device. This can be represented by the formula I = V/R, where I is the maximum current, V is the maximum voltage, and R is the resistance.

What factors can affect the maximum current?

The maximum current can be affected by the voltage, resistance, and temperature of the circuit or device. Higher voltage and lower resistance will result in a higher maximum current, while higher temperature can decrease the maximum current.

Why is it important to calculate the maximum current?

Calculating the maximum current is important for ensuring the safety and functionality of a circuit or device. By knowing the maximum current, the appropriate components and wiring can be chosen to prevent overheating and potential damage.

Can the maximum current be exceeded?

Yes, the maximum current can be exceeded, but this can result in damage to the circuit or device. It is important to ensure that the maximum current does not exceed the components' limits to prevent malfunction or even fire hazards.

Similar threads

Replies
3
Views
1K
Replies
6
Views
4K
Replies
1
Views
4K
Replies
5
Views
2K
Replies
4
Views
10K
Back
Top