The total charge that has entered a circuit element is q(t) = 6 (1 - e-7t) when t ≥ 0 and q(t) = 0 when t < 0. The current in the element for t ≥ 0 can be represented as i left-parenthesis t right-parenthesis equals Upper B e Superscript negative a t A where B and a are real constants. Determine the values of B and a.

Respuesta :

Answer:

[tex]A=42, B=-7[/tex]

Step-by-step explanation:

The current function of time is defined as follows:

[tex]I(t)=\frac{dq(t)}{dt}[/tex]

where [tex]q(t)[/tex] is the charge function.

For the given charge function of time [tex]q(t)=6\left( 1-e^{-7t}\right)[/tex] we have the following current function:

[tex]I(t)=\frac{d}{dt} \left(6\left( 1-e^{-7t}\right)\right)=42e^{-7t}[/tex]

In the problem it is proposed that [tex]I(t)=Be^{-At}[/tex].

Examining the expression of [tex]I(t)[/tex] we obtained by deriving [tex]q(t)[/tex] with the expression proposed by the problem and comparing term by term:

[tex]I(t)=Be^{-At}=42e^{-7t}[/tex]

We conclude that [tex]A=-7[/tex] and [tex]B=42[/tex].