Experiment 11: Measuring a human hair

10/9/2012

In this experiment, we used two different methods to measure the thickness of a hair. Accurately measuring the thickness of a human hair can appear to be a difficult undertaking. However, with the aid of a laser or a a micrometer, we find that obtaining this measurement is not as difficult as we may thought.

First, we using a note card and make a clean hole. Then tape a hair across the hole in the card so that the hair is taut. Clamp the card so that it is parallel to the white board. Mount the laser so that it points perpendicularly toward the wall through the hole in the card. Note the wavelength of the light that the laser emits. Measure the distance from the card to the whiteboard. 

 We try to tape the hair in the middle of the hole.

 We use a cell phone to hold the card so that it cant move.

 We measure the distance from the white board to the laser which is 147.3cm+/-0.1cm

As you can see, it is existing interference on the white board.

Then use a marker to make points. We made the minima points. 

Then we collected all datas and find the d.

Follow the equation, d=lumda*L/Y which d we got is 0.11mm+/-0.03. And we measured by micrometer is 0.08mm+/-0.01mm. It is still existing a big errors. 

In conclusion, we learned how to use the micrometer to measure and the equation y=lumda*l/d is alright. And we find that when the white board go further. The imagine is turning ambiguous, but if we put the white board too close to the laser, it is hard to measure the distance between the minima.