Calculating Alpha in BJT Common Emitter Circuit

[zee824]

i have been asked in my lab report to calculate alpha in a bjt common emmitter circuit using 2 different formulas and explain why one is misleading.β=Ic/Ib= 537.1*10^-6/6.743*10^-6≈85
α= Ic/Ie=573.1*10^-6/566.357*^-6≈1.011
α=β/β +1≈0.988
i have worked out the two values of alpha where our beta is roughly 85 however I am not sure why alpha when calculated from Ic/Ie is missleading.

i have tried to search on the internet however i have found nothing yet and same with my lecture notes.
any help is very much appreciated and i applogise if this is in the wrong section.
thanks
zee

 

[tiny-tim]

welcome to pf!

hi zee! welcome to pf!

i have been asked in my lab report to calculate alpha in a bjt common emmitter circuit using 2 different formulas and explain why one is misleading.

β=Ic/Ib= 537.1*10^-6/6.743*10^-6≈85
α= Ic/Ie=573.1*10^-6/566.357*^-6≈1.011
α=β/β +1≈0.988

it's asking why (Ic/Ib)/((Ic/Ib)+1) = Ic/(Ic + Ib) is not equal to Ic/Ie

 

[zee824]

hi zee! welcome to pf! it's asking why (Ic/Ib)/((Ic/Ib)+1) = Ic/(Ic + Ib) is not equal to Ic/Ie

hi thanks for the quick reply tiny-tim however in this case they are infact equal since ic+ib=ie but I am still getting different values. i feel it is something to do with the capacitors or the configuration of the resistors that is causing a slight error but I am not sure and I am even less sure about why this is misleading