To make the boiler more efficient, we would replace the resistor with another double the length.
We know that the resistance of the resistor in the boiler is given by R = ρl/A where
Also, the power generated by the resistor is P = i²R where
If i is constant, we see that P ∝ R.
So, to increase the efficiency, the value of the resistance has to increase.
Also, since R = ρl/A and ρ and A are constant, we see that R ∝ l.
Since P ∝ R and R ∝ l ⇒ P ∝ l.
So, to increase the efficiency, we would double the length of the resistor.
So, to make the boiler more efficient, we would replace the resistor with another double the length.
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