09-08-2012, 04:18 PM
Make a Hygrometer with Strands of Hair
hygro meter.docx (Size: 157.34 KB / Downloads: 39)
Abstract
Does your hair go crazy when the weather turns damp? Did you know that strands of hair can relax and lengthen when the humidity increases and then contract again when the humidity decreases? In fact, hair strands can be used as the basis for a hygrometer, a device which measures the humidity level in the air. Will a hygrometer help you to predict bad hair days(!) or can you use it to help predict the weather?
Objective
The goal of this project is to make and use a hygrometer, an instrument for measuring the level of humidity in the air.
Introduction
Changes in humidity are an important part of daily weather. In this project you will build an instrument to measure the humidity level in the air. The instrument is called a hygrometer, and it's sensing element is strands of human hair.
In order to understand how a hygrometer made with strands of hair works, it is important to understand the structure of a shaft of human hair. Figure 1, below (Tobin, 2006), illustrates the microscopic structure of a human hair. The left-hand panel of the illustration (Figure 1a), is a cartoon of a human hair shaft with a cut-away view to show the inner structure. Each strand of hair has an outer layer of flattened cuticle cells (Cu), which surround the fibrous cortical cells (Co). The medulla (Md) is a central core of cells in the hair shaft. Also shown is a microfibril (MF) within a cortical cell. The middle panel (Figure 1b), shows an actual hair shaft under the microscope. You can see how the flattened cuticle cells (Cu) have a scale-like appearance when magnified. The dark central medulla (Md) is also visible. The right-hand panel (Figure 1c), shows a cross-section of a fine human hair. Here you can see that the cuticle cells (Cu) are highly flattened, and wrap around the cortical cells (Co) in many layers. The cortical cells contain the dark pigment granules that give each hair strand its natural color.