[填空题]
A beam of monochromatic light is incident on a single slit of width $b$. After passing through the slit, a diffraction pattern is observed on a screen of distance $D$ from the slit.
1.What is meant by monochromatic light?
2.A student wants to measure the width of the central bright fringe of the diffraction pattern observed on the screen.
(1)The width of the central bright fringe is too small to be measured. Suggest three changes in the arrangement to solve this issue when each of them is implemented separately.
（2）The width of the central bright fringe is measured as 2.4 cm after the relevant change in the arrangement is implemented. The distance $D$ between the slit and the screen is 50 cm while the wavelength of used light is 600 nm. Estimate, in $m$, slit width $b$. b = $\times 10^{-5}m$
3.The student wants to be sure of the calculated value of slit width. They therefore decide to repeat the experiment with different wavelengths.
On the axes below, sketch a graph to show how the angle θ of the first diffraction minimum from the central maximum varies with wavelength.
(There is no need to add values to the axes)
