The essence of transistor operation is that a change in vBE, vBE, produces a change in iC, iC. By keeping vBE small, iC is approximately linearly related to vBE, iC = gm vBE, where gm is known as the transistor transconductance. By passing iC through RC, an output voltage signal vO is obtained. Use the expression for the small-signal voltage gain in Eq. (7.20) to derive an expression for gm. Find the value of gm for a transistor biased at IC = 0.5 mA.