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### Project Help!

Posted: Mon Mar 23, 2015 8:46 am
I have participated to Google Science Fair 2015. I want to make a project on 'Dark Matter' and 'Dark Energy'. But, as there's no way to detect them, I don't clearly know what to do. Will I need to make an experiment? Can I publish my idea instead? If neither, will I have to change the topic?

### Re: Project Help!

Posted: Wed Mar 25, 2015 7:16 am
Hello rijuchaudhuri,

Welcome to the forum. “Dark Matter” and “Dark Energy” are a couple of very broad topics. I think it would be helpful if you could try to find some specific areas of interest within either topic. That would make it much easier to develop a project.

I'm not too familiar with the Google Science Fair. I did find rules for projects submissions and it appears to me that an experiment should be part of your project.

I hope this helps and good luck with your project. Please post again if you have more questions.

A. Norman

### Re: Project Help!

Posted: Sat Jul 11, 2015 9:33 am
I have selected a project from this site http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_p066.shtml but I am not able to make out what is the use 10 M ohm resistor used in the circuit. If anyone could explain me by seeing the photo it would be of great help.

### Re: Project Help!

Posted: Sat Jul 11, 2015 11:28 am
In that circuit, R3 (the 10M resistor) serves as a current limiting resistor to make sure that not too much energy flows from the battery when the circuit formed by the two 100K resistors is conducting. Basically, pin 1 of the chip (connected to R1) is always going to be high or a logic '1'. Pin 2 (connected to R2) will be low or a logic '0' when the circuit is dry because there's no conduction between the two resistors R1 & R2, and R3 is providing a connection to ground. When the resistors can conduct due to moisture, the current can flow through all of R1, R2 and R3 making pin 2 high. When both of the inputs are high, the output at pin 3 can go low and turn off the LED.

### Re: Thanks

Posted: Mon Jul 13, 2015 2:55 am
Thank you very much!! That was really helpful