Resistors: Questions & Answers Explained

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In summary, the conversation is about a person seeking help with resistor questions and someone offering tips and advice on how to solve them. The first problem has a resistance of 9.6ohms and the second has a resistance of 0.55ohms. The person suggests redrawing the circuits and using Wye-Delta transformations. They also mention looking for symmetries in the circuit to make calculations easier. For the second problem, they suggest adding a virtual voltage source and finding the voltage drops for each resistor to solve the problem without using simultaneous equations. They also mention that the circuit in b) is easier to solve than a) despite its appearance.
  • #1
pandaboi
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Homework Statement



c8RVcDy.png
I'm not sure how to do these. Other resistor questions are relatively easy but these had me stumped.
An explanation for them would be helpful since all I got are the answers.

The first one is 9.6ohms, second is 0.55ohms.

Not sure if this is advanced but I'm seeking an explanation for these guys. Much thanks!
 
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  • #2
It can help to redraw the circuits.
 
  • #3
Are you familiar with Wye-Delta transformations?
 
  • #4
When given structures like that in (a), ALWAYS first look closely to see whether it has a particular symmetry. If present, this can make calculations SO MUCH EASIER! :wink: :wink:

Do you see a symmetry in the resistance values in that figure?
 
  • #5
pixatlazaki said:
Are you familiar with Wye-Delta transformations?

Don't think they are needed for these two problems. There are more obvious ways to simplify them.
 
  • #6
Hello pandaboi,

Welcome to Physics Forums! :smile:

pandaboi said:

Homework Statement



c8RVcDy.png



I'm not sure how to do these. Other resistor questions are relatively easy but these had me stumped.
An explanation for them would be helpful since all I got are the answers.

The first one is 9.6ohms, second is 0.55ohms.

Not sure if this is advanced but I'm seeking an explanation for these guys. Much thanks!

For part b), it might help to draw a "virtual" voltage source connected between X and Y (by that I mean connect the positive terminal to X and the negative terminal to Y). Ultimately, you want to find the current though that voltage source, so that you can divide its voltage by the current through it, and then you've found the overall resistance.

Once you've included the voltage source, stop and think about what the voltage drop must be for each of the resistors in the circuit. Sure, you could use Kirchhoff's circuit laws and solve a set of simultaneous equations (which will work -- it's a perfectly valid way to solve this), but there may be a simpler way than that for this particular problem. If you find each resistor's voltage drop, you can find the currents through each resistor, and then ultimately the current though the voltage source. You'll still need to heed Kirchhoff's laws, but you might be able to skip the tedium of solving simultaneous equations (for this particular problem).

Btw, part a) is easier because it has that symmetry that NascentOxygen mentioned. But if it didn't have that symmetry, this process I describe of adding a virtual voltage source and solving the simultaneous equations is a sure-fire way to solve these (even problems that don't have shortcuts like these). :wink:
 
  • #7
I think part b) is easier than a).

The circuit in b) is trivial. It can be very easily simplified. It's drawn to make it look hard.
 

FAQ: Resistors: Questions & Answers Explained

What is a resistor and how does it work?

A resistor is an electronic component that restricts the flow of electric current. It is made of a material that has high resistance, which means it resists the flow of electrons. This resistance causes a drop in voltage, which helps to control the flow of current in a circuit.

What are the different types of resistors?

There are several types of resistors, including carbon composition, carbon film, metal film, and wirewound resistors. Each type has different properties and is used for different purposes. For example, carbon composition resistors are inexpensive and commonly used in low-power applications, while wirewound resistors are more expensive and used in high-power applications.

How do I read the color bands on a resistor?

Most resistors have color bands that indicate their resistance value. The first two bands represent the first two digits of the resistance value, the third band represents the number of zeros, and the fourth band represents the tolerance (how close the actual resistance is to the stated resistance). There are online calculators and charts available to help you decipher the color bands.

Why are resistors important in electronic circuits?

Resistors are important in electronic circuits because they help to control the flow of current. They can be used to limit the amount of current that flows through a circuit, protect other components from damage, and adjust the voltage level in a circuit. They are also used in voltage dividers, which are used to reduce the voltage in a circuit.

How do I choose the right resistor for my circuit?

Choosing the right resistor for your circuit depends on the amount of current and voltage in the circuit, as well as the resistance value needed. It is important to consider the power rating, tolerance, and type of resistor when selecting one for your circuit. You can use online calculators or consult a datasheet to help you choose the right resistor for your circuit.

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