# Answer to Question #6281 in MatLAB | Mathematica | MathCAD | Maple for Mark

Question #6281
i(t)=(V/R) * (1-e^-(R/L)(t))

(a) Defi ne an anonymous function answerE that returns i(t) given input t.
(b) The final value for the current is 2 amps. Find a time tm when the
current is at least 99% of the nal value but strictly less than 2. Store
this value in the variable answerF.
(c) Create a vector in answerG using linspace with ten evenly spaced
elements where 0 as the first element and tm as the last element.
(d) Create a vector in answerH which contains the current at each time in
vector answerG.
1
Expert's answer
2012-02-07T14:02:12-0500
a) To define an anonymous function answerE that returns i(t) given input t run the command:

answerE=@(t)(V/R[/url])*( 1-exp(-(R*t/L)) );

b) We have that the final value for the current is 2 amps.
This means that V/R = 2.
In order to find tm we need to know the value of R/L.
In other words we should give some values for V, R, L.

So set some values and then redefine the function:

V=2;
R=1;
L=0.5;
answerE=@(t)(V/R[/url])*( 1-exp(-(R*t/L)) );

To find a time tm when the current is at least 99% of the final value but strictly less than 2,
and store this value in the variable answerF, run

answerF = fsolve(@(t)answerE(t)-0.99*V/R,1)

we will get the result:

&gt;&gt; answerF = 2.3026

(c) To create a vector in answerG using linspace with ten evenly spaced elements where 0 as the first
element and tm as
the last element run

answerG=linspace(0,answerF,10)

which will give the output

&gt;&gt; answerG =
&gt;&gt; 0.00000 0.25584 0.51169 0.76753 1.02337 1.27921 1.53506 1.79090 2.04674 2.30259

(d) To create a vector in answerH which contains the current at each time in vector answerG
run

answerH=answerE(answerG)

which will give the output

&gt;&gt; answerH =
&gt;&gt; 0.00000 0.80103 1.28124 1.56911 1.74169 1.84515 1.90717 1.94435 1.96664 1.98000

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