ov. 15, 2016 (Version B) Show all work to partial t digits. Answer must include

Question

ov. 15, 2016 (Version B) Show all work to partial t digits. Answer must include proper units to be er right. Use the backside you need additional receive partial credit. Round all e one): Problem #6 (7 pts.) You are tasked to design an LED flashlight with a 6V battery pack and two identical LEDs. The forward voltage (or voltage drop) of each LED is 2.5V. The desired current draw for each LED iss? mA. There are two competing designs as shown in the figures on the right. a What would be the resistances of RI and b) What would be the resistances of R3 R2 needed for Design A? (2 pts.) needed for Design B? (1 pt.) c) What is the power consumption of each LED? (2 pts.) d) What is the current draw from the 6V battery in Design A? (1 pts.) e) What are the advantages and disadvantages of Design A compared to Design B? (1 pts.) use more Power

Explanation / Answer

a.) Refer Design A,

Battery Voltage, Va = 6V

R1 = R2 = ?

LED Current = 50 mA =0.05 A

Both the resistances are in series with respective LED and the circuits have same voltage across i.e. 6V

R1 = R2 = Voltage across Resistor / Current through the LED

= (6 - 2.5) / 0.05

= 3.5 / 0.05

= 70 ohms

b.) Refer Design B,

Battery Voltage, Vb = 6V

R3 = ?

LED Current = 50 mA =0.05 A

Both the LED are in series with resistor and the overall circuit have voltage of 6V across terminals.

R3 = Voltage across Resistor / Current through the LED

= (6 - 2.5 - 2.5) / 0.05

= 1.0 / 0.05

= 20 ohms

c.) Power consumed by each LED = VI = 2.5 x 0.05 = 0.125 W

d.) In Design A, same battery is supplying to two branches of circuit which are in parallel. Hence, the total current supplied is the sum of current in each branch i.e. 50 + 50 = 100 mA

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