*Phy*How to tackle such questions?

Please refer to the question down the thread

First define a variable Rq for the resistance of Q. Then write an expression for the resistivity of the wire that P is made of, and an expression for the resistivity of the wire that Q is made of.

Is that enough of a hint? If not, post your attempt.

I can't do this furthur I'm sooo confused
Hey wait Rq part is wrong i forgot to sqaure the 2 aswell the final ans would be Resistivity×L/pi d^2

By the way, this is my version of the step you posted above. You can take this forward substituting rho as I mentioned above, but there is a shortcut. Can you spot it?



The other thing I'm gonna say is, before you even start the calculation, you could think about the relative thickness and length of P and Q. Are you expecting Rq to be more or less than Rp? Having this in your mind will help you notice if you make a silly mistake in your calculation.

Yay! You got it. Don't assume anything though. Work it through, like this:



Did you think about what you were expecting the answer to be? As Q is thicker than P, that will make it lower resistance, right? Also, as Q is shorter than P, that also makes it even lower, right? Well, our answer says it's 8 times lower than P, so that's good - at least it's a quick check that we didn't make some huge error.

Are you all clear on this now?

Yay! You got it. Don't assume anything though. Work it through, like this:



Did you think about what you were expecting the answer to be? As Q is thicker than P, that will make it lower resistance, right? Also, as Q is shorter than P, that also makes it even lower, right? Well, our answer says it's 8 times lower than P, so that's good - at least it's a quick check that we didn't make some huge error.

Are you all clear on this now?

can you please check this aswell?Am I solving this correct?
the ratio is 8:1

Could you post the start of the question, so I can see the circuit diagram?

Did you notice how much cancelling out goes on with these calculations? You can save some writing if you think about the proportionality. In fact, once you get comfortable, you could almost see the answer direct from the table. I've posted an alternative solution below using this method. If you get it, that's great - it's a more advanced understanding and will help you do the questions quickly. If you're not sure, you can always use the full method you used above.

Thank you so much honestly you explained it so well I tried solving few more questions and I finally learned how to solve these type of questions thank you^-^