Math Is Fun Forum

don.farr

Member

Registered: 2020-11-24

Posts: 3

I'm in trouble of 10 and exponent math.

A)    VL =    Δi /Δt
    (200*10-6) ((200*10-3)/2*10-6)
       0.002       ((   2        ) / 0.00002)
       0.002 * 1OOOOO
        200V

B)    VL =    Δi /Δt
    (200*1.0e-6) ((200*10-3)/2*10-6)
       0.02       ((   2        ) / 0.00002)
       0.0002 * 1OOOOO
        20V

Where VL = Instant voltage on an inductor
Δi = Change in amperage
Δt – Change in time

The answer given in the textbook is “20 volts” However, using the book’s formula (A) I come up with 200V instead of the answer of 20V
So I created process “B” and I get the correct answer, but I cannot not explain why there is a difference between using the “Micro value (10-6) and using the exponent value 1.0e-6”

Last edited by don.farr (2021-01-02 07:36:06)

Bob

Administrator

Registered: 2010-06-20

Posts: 10,626

Re: I'm in trouble of 10 and exponent math.

hi don.farr

I'm confused in trying to compare your two methods.

In B

(200*1.0e-6)

What does this mean?

1.0 x e^-6 is a different thing altogether.  e raised to the power -6 would not be a simple power of ten.

Are you using the 'exp' key on a calculator here.  That would make this 1.0 x 10^-6 which makes this the same as A.

Also

0.02       ((   2        ) / 0.00002)
       0.0002 * 1OOOOO

Here you have changed 0.02 into 0.0002.  I cannot see why.

This physics is not my area but I can substitute values into a formula and evaluate.  Please go back a step and say where the values have come from.  Then I'll try to see what the correct evaluation is.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

don.farr

Member

Registered: 2020-11-24

Posts: 3

Re: I'm in trouble of 10 and exponent math.

Good morning Bob and thanks for your help.  Yes I am using the exponent key on a calculator.
No matter how I do this, problem (A) is supposed to resolve to 20A.  I get 200A using the equation given in (A)

The textbook equation is give in (A) without any changes.  So I ask, what am I doing wrong in my evaluation of the formula?   Is it possible that the formula is incorrect or the answer given is incorrect?

zetafunc

Moderator

Registered: 2014-05-21

Posts: 2,436

Website

Re: I'm in trouble of 10 and exponent math.

Hi don.farr,

Welcome to the forum. I believe you're missing out a factor of 10 in your multiplication -- note that:

This might help:

I'm getting 20 as the correct answer when I run through your calculation in A. Let us know if you need any more help!

don.farr

Member

Registered: 2020-11-24

Posts: 3

Re: I'm in trouble of 10 and exponent math.

Got it.  I was using the wrong button on the calculator.  I was using the exponent button instead of power button.  Thanks!!!!!