Exponential revision question I can't work out?

[Ramjam]

opps sorry that should be -i/12.5-1=e^-t/cr

 

[Mark44]

opps sorry that should be -i/12.5-1=e^-t/cr

No, that's not right either. You really need to be more careful.

 

[Ramjam]

in that case i don't under what you mean by

After you multiplied by -1, what happened to the -1?

 

[Mark44]

What is -1 times i/12.5 - 1?

If you're having such a difficult time with basic algebra, I am very concerned about the prospects of you working with exponential and log equations.

 

[Ramjam]

What is -1 times i/12.5 - 1?

If you're having such a difficult time with basic algebra, I am very concerned about the prospects of you working with exponential and log equations.

It was 2am in the uk and after a long working day which i also do along side my course probably wasn't the best idea.

Right here are my working so far now that I've been had some sleep,

we start with I=12.5(1-e^-t/cr)

I then divide both sides by 12.5 removing the 12.5 from the right hand side.

I/12.5 = 1-e^-t/cr

I then subtract -1 from both sides

I/12.5 -1 = -e^-t/cr

I then times both sides by -1 giving me

(1- I/12.5) = e^-t/cr

how ever to remove I am unsure of how to go on from here?

 

[ehild]

You need the time when the current I reaches the value I=10 A. Note that 12.5 is also in amperes. Substitute 10 for I and evaluate the left side of the equation.
Also calculate cr, or better CR from the given value of capacitance C and resistance R.