Science Buddies: "Ask an Expert"

I am working on the below project and was able to make the LED flicker (Generate Electricity)
https://www.homesciencetools.com/produc ... icity-kit/

My question is I am trying to measure the voltage using multimeter while the LED is flickering , I read only 5.3 mV, I felt that it is too low voltage and LED cannot flicker with this voltage , but I see 4 LED flicker with this voltage ..

am I measuring the correct voltage ? I was under the impression that I should measure atleast 5V+.

Note: I checked the multimeter with other source and able to read the correct volatage..
could you please clarify me , why I read low voltage ? or is what we expect ?

Hi aferoz77,

Your intuition is correct - 5.3mV is not enough to light an LED. The problem is with attempting to use a multimeter to make this measurement.

You probably have your multimeter set to measure the voltage of a direct current, usually marked by a "DC" or a straight line over a "V" on the multimeter dial. Roughly speaking, direct current means that the current is constant and flows in the same direction - not flickering on and off or changing directions. For example, that's the type of current you get in a circuit powered by a battery, and that's probably what you did when you measured another voltage source with your multimeter.

With this project, you are shaking the magnet back and forth rapidly so the current is flickering on and off, which is why the LED flickers instead of staying on continuously. So, the multimeter setting for DC voltage doesn't give you an accurate reading, because it requires a direct current. Some multimeters are also capable of measuring the voltage for an alternating current (AC), or a current that switches directions. That may give you a better result, although it still may not be 100% accurate - I believe the settings for AC assume the current goes between two equal positive and negative peaks, whereas in this project it goes between a positive peak and zero, since the LEDs only let current flow in one direction.

Here are some resources of ours that might be helpful:

https://www.sciencebuddies.org/science- ... eter#qACDC

https://www.sciencebuddies.org/science- ... r#qsymbols

https://www.sciencebuddies.org/science- ... ial#dcvsac