TBR Example 9.1b

[golgiapparatus88]

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I'm stuck on this conceptual problem. "For a fixed potential difference across a resistive wire, the power loss through the resistor can be increased by increasing the:
A. neutron density in the wire
B. Length of the wire
C. Temperature of the wire
D. Conductivity of the wire

The correct answer is D. I must be missing something conceptually because most of them actually sound like good answers. Increasing the neutron density would increase the resistivity as would increasing the length AND so would increasing the temperature. Power is equal to current * voltage or current^2 * Resistance so if resistance increases, the power loss would increase as well.

 

[Pisiform]

I'm stuck on this conceptual problem. "For a fixed potential difference across a resistive wire, the power loss through the resistor can be increased by increasing the:
A. neutron density in the wire
B. Length of the wire
C. Temperature of the wire
D. Conductivity of the wire

The correct answer is D. I must be missing something conceptually because most of them actually sound like good answers. Increasing the neutron density would increase the resistivity as would increasing the length AND so would increasing the temperature. Power is equal to current * voltage or current^2 * Resistance so if resistance increases, the power loss would increase as well.

Increasing Temp/neutron/length increase resistance.

P = V^2 / R

Since Power is inversely proportional to Resistance, increasing resistance decrease power.
But, we are looking for the thing that increase power loss. So, D is correct.

Also, you cannot used P = I^2 R formula in this case because you are looking at a relationship between Power, Voltage(p.d), Resistance. So you need Voltage in the power formula so that you can fix (constant) it. Then only you can come up with a relationship of P inversely prop. to R.
Hope this helps

 

[golgiapparatus88]

Increasing Temp/neutron/length increase resistance.

P = V^2 / R

Since Power is inversely proportional to Resistance, increasing resistance decrease power.
But, we are looking for the thing that increase power loss. So, D is correct.

Also, you cannot used P = I^2 R formula in this case because you are looking at a relationship between Power, Voltage(p.d), Resistance. So you need Voltage in the power formula so that you can fix (constant) it. Then only you can come up with a relationship of P inversely prop. to R.
Hope this helps

Thanks 🙂