Version A was given at 4th period, Version B was given at 6th period. The spectrum of the hydrogen atom is directly related to hydrogen's atomic structure. All elements, such as hydrogen, have very specific energy levels at which its electrons may reside. Refraction is the bending of light rays upon passing from one transparent medium to another. For example, light that passes from air through a glass lense and then back to air will be bent from its original direction in a very predictable way.
Reflection is the bouncing of light off of a reflective surface, such as a mirror.
Reflection simply changes the direction of the light. The direction change can be controlled in a very accurate way if the shape of the mirror is precisely known. Refractive telescopes gather light from a large area, direct that light through a precisely shaped lense, which focuses the light onto a smaller area which can be viewed by a person or detector. Reflective telescopes use spherical, elliptical, parabolic, or hyperbolic shaped mirrors to focus light from a large area onto a smaller area. By using several mirrors, the light path can be contained into a smaller area.