Page:Calculus Made Easy.pdf/68

 (14) The electromotive-force necessary to maintain an electric arc of length $$l$$ with a current of intensity $$i$$ has been found by Mrs. Ayrton to be

$E=a+bl+\frac{c+kl}{i}$,

where $$a$$, $$b$$, $$c$$, $$k$$ are constants.

Find an expression for the variation of the electromotive-force $$(a)$$ with regard to the length of the arc; $$(b)$$ with regard to the strength of the current.