Issue with exponents in inductance - Page 1
Forum section: electronics / beginners

author: Mati256
author_rank: Contributor
timestamp: October 30, 2014, 07:07:21 pm
content: Hello. I'm studding for an exam and I came across this exorcise, after I did it I check the answer to find that my maths are wrong.Am I or is the exorcise wrong?104x 500x10-6= 50 Ohms right?

author: Andy Watson
author_rank: Super Contributor
timestamp: October 30, 2014, 07:17:47 pm
content: Careful how you push the buttons on your calculator. 10^4 is 10000, not 10 exp 4 (which a calculator will treat as 10 x 10^4).

author: Mati256
author_rank: Contributor
timestamp: October 30, 2014, 07:37:32 pm
content: You are rihgt!Thank you!

author: IanB
author_rank: Super Contributor
timestamp: October 30, 2014, 08:05:55 pm
content: This is why engineers should practice doing estimates on paper or by mental arithmetic and not rely too much on button pushing.From high school maths:104x 500x10-6= 500 x 106x 10-4= 500 x 10(6-4)= 500 x 10-2= 500 / 100= 5

author: Refrigerator
author_rank: Super Contributor
timestamp: October 30, 2014, 08:20:44 pm
content: Quote from: IanB on October 30, 2014, 08:05:55 pmThat's pretty much exactly the same math they were teaching in my school last week, incredibly easy and boring, you don't even need a calculator to solve these kind of equations.

author: Timmay
author_rank: Contributor
timestamp: October 31, 2014, 04:38:02 am
content: Quote from: IanB on October 30, 2014, 08:05:55 pmTrue but as I put this in my TI, mathway, matlab, excel, wolfram and my cellphone I got the correct answer. So as much as you should easily should be doing this by hand, you should equally know how to do it on a calculator or equivalent program. If you make mistakes often, then it shows you don't quite understand the concepts behind the math and that can be a problem. We all make mistakes, but calculators are key to anyone in any STEM field.

author: IanB
author_rank: Super Contributor
timestamp: October 31, 2014, 05:23:50 am
content: It's not a question of doing it by hand instead of doing it on a calculator, it is a question of knowing how to estimate whether the answer you got out of the calculator is in the right ballpark, just in case you made a button pressing error. So for example, you should know how to tell by eye whether the answer should be about 0.5 ohms, 5 ohms or 50 ohms, even if the exact answer happens to be 57.3 ohms.

author: VK5RC
author_rank: Unknown
timestamp: October 31, 2014, 08:12:40 am
content: This was where slide rules taught you a lot. You always did an order of magnitude calculation in your head.

author: Timmay
author_rank: Contributor
timestamp: November 02, 2014, 09:07:31 am
content: Quote from: IanB on October 31, 2014, 05:23:50 amI concede, very true. I will add that confidence in both your written and calculated answers is important and that with time, learning enough of the concepts behind it all will lead you to the point IanB makes. Maybe take an approach my school did: Calculated, Simulated and Physical. With math you do the problems and find your answers, then simulate them with some decently cheap software like Multisim and if time permits use a breadboard approach to go into it more. However, as I agree with IanB knowing all the angels of a problem, doing them more and more often will get you to the point IanB makes.