1. The problem statement, all variables and given/known data Consider the following circuit http://img109.imageshack.us/img109/80/circuit1.jpg [Broken] IL, current through R3 (unknown resistance must be found) 2. Relevant equations Vth=(Vcc/Rtotal)*R1 (V tThevenin) Rth=R1//R2 (R Thevenin) Vbe= 0.7 volts (silicon diode) Beta (transistor constant)=100 Vcc=10v IL=Beta*Ib Ie=Ib + IL 3. The attempt at a solution I used the following Equation to try and obtain an answer. Vcc= (Ib*Rth)+ (Ie*R4) + Vbe + Vth Vth=5v Rth=2.5k Ohms Substituting gives: 10=(IL/Beta)*(2.5k) + 1000*(IL*((Beta +1)/Beta)) + 0.7 + 5 This yields an answer of IL=4.15mA. My tutor said this is a wrong answer, the correct one is 4.3mA What is wrong in my reasoning/Working?