Understanding Voltage Drop in a Circuit

In summary: I will be careful in future and I will reply as you have explained. Thank you for your understanding and answer.
  • #1
Lay1
44
7
Homework Statement
Refer to the figure. Assume the green LED drops 2V across it when it is on. The maximum current in the LED is to be set at 10mA and the minimum current is 2mA. Choose values for R1 and R2 to meet these requirements.
Relevant Equations
V=IR
Here is the figure mentioned above.
20230413_182850.jpg

My thinking is that for maximum current, resistance must be minimum. Thus, R1 is not considered which means the voltage drop of R2 is 10V. So, R2 is 1kohm. For minimum, I=2mA, so R1+R2=5kohm, since R2 is 1kohm, R1 must be 4kohm. This is how I deduce. However, the answer shows that R1=5kohm while R2 is 1kohm. I do not understand why it is so. Could someone help me explain why? Thank you as always.
 
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  • #2
Lay1 said:
For minimum, I=2A, so R1+R2=5kohm, since R1 is 1kohm, R2 must be 4kohm. This is how I deduce.
Change the I=2A typo to I=2mA and I agree with you. I think the solution's answer for the minimum current case is incorrect.
 
  • #3
Lay1 said:
Thus, R1 is not considered which means the voltage drop of R2 is 10V. So, R1 is 1kohm
R1 is not considered and R1 is 1kohm?
 
  • #4
cnh1995 said:
R1 is not considered and R1 is 1kohm?
Oh, good catch. Another typo! :smile: Yeah, we need the OP to add a reply with the R1/R2 stuff cleaned up.
 
  • #5
berkeman said:
Change the I=2A typo to I=2mA and I agree with you. I think the solution's answer for the minimum current case is incorrect.
Thank you for your guidance. And also thank you for your confirmation.
 
  • #6
cnh1995 said:
R1 is not considered and R1 is 1kohm?
I am really sorry for my careless mistake. And thank your for your correction.
 
  • #7
Lay1 said:
Thank you for your guidance. And also thank you for your confirmation.
Wait, did you see where there are other typos as well? Please reply with the correct values for R1 and R2, where R2 is the fixed resistance to define the maximum current, and R1 is the variable resistance to define the minimum current when added to R2.
 
  • #8
berkeman said:
Oh, good catch. Another typo! :smile: Yeah, we need the OP to add a reply with the R1/R2 stuff cleaned up.
I have already fixed. Sorry for your inconvinience.
 
  • #9
berkeman said:
Wait, did you see where there are other typos as well? Please reply with the correct values for R1 and R2, where R2 is the fixed resistance to define the maximum current, and R1 is the variable resistance to define the minimum current when added to R2.
My answer: R1=4kohms and R2=1kohm
The textbook answer: R1=5kohms and R2=1kohm
 
  • #10
Lay1 said:
I have already fixed. Sorry for your inconvinience.
Oh, okay, I see that now. I still agree with the two values you calculated.

For future reference, it's usually best to add a reply to correct any typos that have been mentioned in your Original Post (OP). Otherwise the replies afterward that point out the typos can be confusing for others reading the thread later. It's okay to leave it as-is for now.
 
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  • #11
berkeman said:
Oh, okay, I see that now. I still agree with the two values you calculated.

For future reference, it's usually best to add a reply to correct any typos that have been mentioned in your Original Post (OP). Otherwise the replies afterward that point out the typos can be confusing for others reading the thread later. It's okay to leave it as-is for now.
I will be careful in future and I will reply as you have explained. Thank you for your understanding and answer.
 
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FAQ: Understanding Voltage Drop in a Circuit

What is voltage drop in a circuit?

Voltage drop refers to the reduction in voltage as electric current flows through the components of a circuit. This occurs due to the resistance or impedance of the circuit elements, such as wires, resistors, and connectors. The voltage drop is the difference in voltage measured between two points in a circuit.

Why is understanding voltage drop important?

Understanding voltage drop is crucial for designing and analyzing electrical circuits to ensure they operate efficiently and safely. Excessive voltage drop can lead to poor performance of electrical devices, overheating, and potential damage to the components. It is essential for maintaining the integrity and reliability of electrical systems.

How do you calculate voltage drop in a circuit?

Voltage drop can be calculated using Ohm's Law, which states that V = I * R, where V is the voltage drop, I is the current, and R is the resistance. For a more complex circuit, the total voltage drop is the sum of the voltage drops across each component. For AC circuits, impedance (Z) is used instead of resistance, and the formula becomes V = I * Z.

What factors affect voltage drop in a circuit?

Several factors affect voltage drop, including the resistance of the conductors, the length and cross-sectional area of the wires, the amount of current flowing through the circuit, and the quality of the connections. Higher resistance, longer wires, smaller cross-sectional areas, and higher current all contribute to greater voltage drops.

How can you minimize voltage drop in a circuit?

To minimize voltage drop, you can use conductors with lower resistance, such as thicker wires or materials with higher conductivity. Reducing the length of the wires and ensuring tight, clean connections can also help. Additionally, distributing the load evenly and using voltage regulators or boosters can mitigate excessive voltage drop in a circuit.

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