Al Given that for the purpose otf byT-14R,C and R0R. Find the unimown resistors

Question

Al Given that for the purpose otf byT-14R,C and R0R. Find the unimown resistors if we want a period of Q.7 s, and the onily capacitor we have has a 22-pF capacitance. 50%duty cycle, the periodofthe tiner is given B] Given that a photoresistor (a resistor whose resistance changes with the amount of light that hits it) replaces the resistor Rs, and that the frequency of the output of the timer increases as more light hits it, explain whether the resistance increases or decreases with light (possible device with a speaker attached to the output to keep the refrigerator door from being open too long, assuming that the low frequency when it is dark is not audible).

Explanation / Answer

Given that for the purpose of appproximately 50% duty cycle , the period of timer is given by T= 1.4R2C .
R2= 10 R1 , Time period given is 0.7s, Given C= 22 micro farad
therefore 0.7 = 1.4R2C
= 1.4* 10 R1*C
0.7= 1.4* 10 R1*22*10-6
therefore R1 = 0.7/(1.4*22*10-6*10)
R1= 2272.72 ohms
R2= 10* 2272.72 = 22727.2 ohms
Given that the photo resistor is replaced with the resistor R2 . Photo resistor is a device whose resistance value decreases with the increase of the light intensity. The frequency of the output of the timer increases when more light hits the photo resistor.
consider the refridgerator, when the refrigerator is open the light intensity inside the device is very high. hence the resistance is very low. When the door is closed then the resistor value is increased to a high value which decreases the light intensity on the photo resisitor.

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