Transistors are often used to drive actuators, since we can use small currents from, say, computer interfaces to control the larger currents the actuators need. Consider the circuit below. NOTE: D1 is there to "clamp" the L di/dt voltage that occurs during switching; ignore it in this analysis. You'd find that it is reverse biased anyway :-)
V1 18V
R1 R=???
R2 100k
K1 N=500
Q1 B=-150
D1
If actuator K1 is an LSA with a plunger diameter of 1 cm, what must the value of R be for it to deliver 20 Newtons of force? Assume Q1 is an npn transistor made from silicon with B=-150. Enter your answer as a whole number in Ohms in the space provided.