# Light dependant resistor Essay

Custom Student Mr. Teacher ENG 1001-04 12 July 2017

## Light dependant resistor

As you can see from these results as the light intensity increases, the resistance decreases. I need to find the range of light levels the LDR can detect and distinguish how sensitive it actually is. The maximum resistance it is possible to get from the LDR is 550k?. This is when there is maximum light shining on the LDR. The minimum resistance that is possible is 0. 90k?. This is when the LDR is submitted to complete darkness.

To Use these LDRs effectively, I need to use two of them connected in series, and as the light moves across form one to another the resistance should decrease in the LDR that has more light shining on it and increase on the one in relative darkness compared to another one. The voltage placed across the resistors and the current flowing through must be the same because it is the same circuit. As we know, The resistance is the voltage divided by current. The resistance over the two LDRs must remain constant but it is how this resistance is divided up between the two that is important.

The resistor with the light shining on it should have a low resistance, while the resistor with no or less light should have a higher resistance. I am going to use two LDRs connected in series on a piece of card at varying distances apart to find the effect of the light shining on them. This is the circuit that I am going to use. Circuit diagrams As you can see when the light levels are the same, the voltages are the same. When the light levels are different, the voltages are different but it still adds up to 12v overall.

The voltage is the same, it is just shared out differently. When the light level is high (400), the resistance is high and therefore the voltage is low. When the light level is low, the resistance is low and therefore the voltage must be high. Voltage always equals current x resistance. I am hoping to use a motor to respond to the difference in voltage or resistance and move to the direction of the light. It will stop when the voltage is the same on both sides i. e. when the light is in the middle of the two LDRs.

They will act as like eyes, locating the light source. The two LDRs are going to be separated by a sheet of card straight down the middle of the card that the LDRs are mounted on. This is so the light falls on one or the other of the LDRs. It will cast a shadow so one of the LDRs will be in perfect light and the other will be in near darkness. As the light nears the middle, the light will fall equally on both. By doing this I am emphasizing the amount of light on the LDRs, creating a bigger difference and more emphasized results.

I am taking the results of the voltage of one of the LDRs. If I took the voltage of both of them, it would always read 12v. The lamp that I am going to use is 12v, 90watt bulb and it is going to be placed 15cm away from the LDRs and it will be moving from right to left at 5cm intervals in front of the LDRs so it will be shining at them from different angles and more importantly, shining on one of them more than the other. It is 5cm because it gives lots of different positions the light can be in so produces a wider range of results.

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• Subject:

• University/College: University of Chicago

• Type of paper: Thesis/Dissertation Chapter

• Date: 12 July 2017

• Words:

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