Daily physical problem T1

Face questions

To see Fig yourself?
Small brush H Seventeen students know almost query the physical learning materials, quite unexpectedly brush to this article: "soften hair thinning hair loss is a sign." To measure the diameter of his hair, he first studied physics for a while, and then if it does not collect a handful of hair. Head hair sandwiched between two parallel glass plates, the air layer is formed wedge-shaped cape (FIG. 1). The monochromatic light is irradiated vertically, fringes of equal thickness is obtained (FIG. 2), the measured distance between the interference fringes, it is possible to calculate the diameter of the hair. The results of a measurement of the wavelength of monochromatic light $l = 589.3nm$ distance, the hair and split apex point $L=28.880mm$ , the distance between the light pattern 30 is $4.295mm$ .
(1) Find the hair diameter $D$ ;
(2)small H is preparing to do the experiment again, this time a dog can be a dog licking brother incarnation, even licking on the experimental equipment. If a liquid is filled between two glass plates, a distance between the light pattern becomes 30 $3.222mm$ , the refractive index of the liquid seek $n$。

Well, we look at the title bar

• First of all, I do not want to paint , I believe we strange imagination, so we can not draw up.
• Look at the first question, imagine this optical path diagram: first ray of morning sunshine sway on the panes, dog brother took out his special skill, drawing precise measurements, he finally drew a good painting of an optical path, then the exams are over
• What does that mean, we know $i =$ ${D}\over{L}$ $\ to0$ , it can be seen directly incident light vertically downwardly emitted vertically upward, the optical path difference $ΔL=2y$ ( $Y$ is the vertical distance between the two plates)
• when $ΔL=kλ=2y$ , the bright stripes appear
• So every appearance $Δy$ meet $l = 2Dy$ , will have alternating bright Shadoweave
• $Δx=$ ${X}\over{N-1}$（ $X=4.295mm,N=30$）。
• We also know, $Δx$与 $Δy$ meet between $\ = Tan$ ${Δy}\over{Δx}$
• That is $Y$ for each additional $Δy=$ ${λ}\over{2}$, Clear dark fringes generated alternately, at this time $x$ increase $Δx=$ ${X}\over{N-1}$
• and $\ Tan \ approxth \ approx \ sin i$
• So have ${D}\over{L}$ $=$ ${Δy}\over{Δx}$ $=$ ${{λ}\over{2}}\over{{X}\over{N-1}}$Substituting the data obtained from $D=57.46μm$
• The second question is similar to the idea, but some kind of liquid into the light after the wavelength is changed ${λ}\over{n}$
• Readily calculated from the above ideas $n=1.33$
• So the dog's saliva brother mysterious liquid is water, ah

Did not, Ye Ye