Induced Emf Calculation

[mpc4000]

hi all just going the trevor Linsey advanced installtion work level 3 and i'm struggling with a calculation regarding average induced emf..the Question is :

The Magnetic flux linking turns 2000 turns of electromagnetic relay changes from 0.6 to 0.4 mWb in 50ms. Calculate the average value of the induced emf.

the working out is on the page and the answer is given as emf= -8V but when i follow the workings out i get a totally differnent answer.

any help in how to work this out would be truly much appreciated

Thanks in advance

 

[baldsparkies]

Is this the formula your using,ie Faradays if not how are you applying your calcs in relation to the answer. If you post it up we can all have a look. I will need to go back lots of years though,

 

[mpc4000]

Is this the formula your using,ie Faradays if not how are you applying your calcs in relation to the answer. If you post it up we can all have a look. I will need to go back lots of years though,

thanks is the calculation thanks
emf = - _(0.6 - 0.4) x10-3___x2000
50 x10-3

i've done the cal and the answers i get is 0.000008 is my answer in mil or something ?

thanks in adavnce to anyone who can shed some light and point me in the right direction

 

[baldsparkies]

Works out at 4120/515 = 8 for me, cant see where all your noughts come from.
Where are the brainy guys hiding.

 

[mpc4000]

Works out at 4120/515 = 8 for me, cant see where all your noughts come from.
Where are the brainy guys hiding.

ok this is where i really embarrass myself here but what the hell i'm sure the answers is staring me in the face but mind you i did spend nearly an hour looking for my mobile phone when i had in in my hand all the time so that s the kind of person you are dealing with but can i just ask how you how come up with the numbers you have ?

thanks

 

[Notsosmart]

I'm not one of the brainy ones but the easiest way of looking at it is to work out the division first;

0.2 x 10-3
50 x 10-3

10-3
10-3 = 1 (so you can ignore)
=

0.2
50

= 0.004 A/s Now multiply by 2000 turns = 8v But it is back emf so dont forget it should be -8v

Hope this helps

 

[mpc4000]

I'm not one of the brainy ones but the easiest way of looking at it is to work out the division first;

0.2 x 10-3
50 x 10-3

10-3
10-3 = 1 (so you can ignore)
=

0.2
50

= 0.004 A/s Now multiply by 2000 turns = 8v But it is back emf so dont forget it should be -8v

Hope this helps

thats made my day ta a mil for that

 

[baldsparkies]

Just seen your reply mpc, when you break the equation down into its relevant sections the answer becomes clear. Glad Notsosmart replied for you, so thanks to him

 

[Electrofreak]

Actually It was Flight left tentant Day that said rules are for obediance of fools and guidance of wise men to Douglas bader. Day did not loose his leggs.
All the same congrats on what i think is a very cool quote!