ENES100_PS4_soln_S09

ENES100_PS4_soln_S09 - ENES 100 Introduction to Engineering...

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ENES 100 Introduction to Engineering Design Problem Set 4 Spring 2009 Problems: 1. In lecture, a wiring schematic was provided which would allow your team to place two CdS photoresistors on a single input port. Suppose your team plans to build a hovercraft that uses a total of eight CdS photoresistors. This requires that two sensors be placed on each port. (a) Based on the table of values for the resistance of each photoresistor at dark/light conditions, what would the NXT digital voltmeter read if Sensor 1 was on black and Sensor 2 was on white? On White On Black Sensor 1 (R1) 5 k Ω 15 k Ω Sensor 2 (R2) 50 k Ω 150 k Ω The NXT’s internal circuitry consists of a 5V source and a 10 k Ω resistor in series. If R1 is 15 k Ω (on black) and R2 is 50 k Ω (on white), the current flowing in the series circuit will be: V=IR eq 5 V = I(10 + 15 + 50)k Ω I = 0.0667 mA The NXT output is determined as the voltage drop across R1 and R2. This is found to be: V measured = IR 1-2 V measured = (0.0667 mA)(65 k Ω ) V measured =4.33 V . NOTE: This is the voltage measured across R1 and R2 which are connected in series across the NXT output port. (b) If the NXT digital voltmeter reads 4.7 V, what would the sensor orientation be? Applying KVL to the circuit loop described above yields: +V s – V d,10k – V d,R1-R2 = 0 5V – V d,10k – 4.7 V = 0 V d,10k = 0.0303 V Applying Ohm’s Law to the 10k Ω
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ENES100_PS4_soln_S09 - ENES 100 Introduction to Engineering...

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