Please solve 1 a,b,c,d,e In the lab 8 Diodes and Rectifiers we discussed how to
ID: 2991309 • Letter: P
Question
Please solve 1 a,b,c,d,e
In the lab 8 Diodes and Rectifiers we discussed how to convert 110 Volts AC from the wall outlet into low DC voltage to power up an electronic appliance. The lab focused on rectifiers, i.e. how using a diode and capacitor we can convert low AC voltage Into low DC voltage. But first however, we need to convert high AC voltage of the outlet into low AC voltage which we feed into the rectifier. The easiest way to achieve that would be to add a large resistor in series with the rectifier. Then the voltage of the outlet would be split between the resistor and the useful load. However, this is a pretty dumb way to do this. One obvious drawback is that a lot of power would be wasted as heat on the resistor. Another problem with this setup is that most devices require a constant voltage to power them up, but they can change the current they consume. I.e. you can?t think of a device as of a simple resistor, It?s effective resistance can change. This is where our setup with a single resistor fails. Problem 1. illustrates this point (for simplicity we consider DC voltage here, instead of AC). 1. A device on fig.1 (say, a laptop), is rated to be always powered by DC voltage V 20 Volts. When it?s idle, it consumes i= 0.8 Amps of current. The power source provides a DC voltage V =110 Volts. What must the value of resistor R be in order to provide required voltage and current to the device? (Hint: you may want to use Kirchhoff?s current and voltage rules) a. (0 pts, yes this question has an obvious answer) What is the current through resistor? b. (1 pt) what is the voltage on the resistor? c. (1 pt) what is the resistance R? Now suppose the device needs to increase the current consumption to i = 0.9 Amps (say, we start a program on our laptop that consumes some of CPU time, so that power consumption increases). The resistance R is the same as calculated in part c. d. (2 pts) What would be the voltage V provided to the device now? (Of course, in practice laptop wouldn?t be able to function properly in this situation) e. (1 pts) Is it possible to increase the current to i = 2 Amps? Why? Of course, it is possible to somewhat improve this simplistic one-resistor design to deal with the problem of the changing voltage, when the current of the useful load changes a little (Look up voltage divider). However the maximum useful current through the load would be still limited, and the power waste as heat on resistors would be still too high. Bottom line, we need something that provides stable low voltage output regardless of the useful load current, and doesn?t generate too much ohmic heat losses as resistors do. And this is what a transformer is used for. We mentioned it solve 1 a,b,c,d,eExplanation / Answer
1.) a) 0.8 Amps
b) v0 - V - Vresistor = 0
110-20-V = 0
V= 90 V
c)
R= V/I
R = 90/0.8= 112.5 ohms
d)
v0 - Vlaptop - I R = 0
Vlaptop = 110- 0.9*112.5= 8.75 V
e)
No since the resistor wont allow that much current
max current = v/R = 110/112.5 = 0.978 A