Lab 4 - DC Circuits: Electric Power Introduction and Theory: In this lab we look at electric power dissipated in a load resistor in a circuit with a real power source, which has a finite internal resistance. We will study how to deliver the most power to a device from a source. We will see that the power you can extract from a real source is maximized for a particular value of load resistor. A real-life example is matching loudspeakers to an audio amplifier. To get the loudest boom-box connection in your car, you should connect an "8 Ωresistance" loud-speaker to an 8 Ωresistance connection on the amplifier. In this lab we will find out why. Objectives: To define the concept of electrical resistance and experimentally determine the load resistance (RL) value at which power is optimized in a DC circuit. Equipment: DC power supply 2 digital multimeters (DMM) 2 decade resistance boxes Connecting electrical leads. Procedure: LLRRRVP200A RRed + Black - V RL
1. Measure Rdirectly using the DMM on ohms range. The “effective” internal resistor must be removed from the circuit! 2. Connect the circuit in Figure above. Your instructor will give you guidance (please do not switch on the power supply until your instructor check your circuit). 3. Measure (I, V) as you step through values of RL. Measure in increments of 10 Ωfor the range of 10 –100 Ω; measure in increments of 20 Ωfor the 120 –200 Ωrange; and measure in increments of 100 Ωfor the 300 –1000 Ωrange. 4. Calculate the power P = I·V dissipated in the resistor for each measurement and make a plot of power P vs. RL. From this plot eyeball the load resistance which maximizes the power output. Final Conclusion: Did you confirm that the power extracted from a circuit is maximized when the load resistance is equal to the internal resistance of the power supply?