Pretend you are a teacher preparing a quiz for the text I will provide. 
            Each quiz question should follow the format below. 
            Ensure that you carefully recheck the questions and answers for accuracy. 
            The output should be a ready-to-use list of dictionaries for the Python eval function:

            [

                    "question": "WRITE THE QUESTION HERE",
                    "options": ["A) OPTION_1", "B) OPTION_2", "C) OPTION_3", "D) OPTION_4"],
                    "answer": INDEX_OF_CORRECT_ANSWER_IN_OPTIONS_LIST,
                    "explanation": "EXPLAIN WHY THE ANSWER IS CORRECT"

            ]

            Text:
             up into a glass tube. The glass tube filled with the mixture of gases acts as an active medium or laser medium.
Types of lasers
Liquid laser
A liquid laser is a laser that uses the liquid as laser medium. In liquid lasers, light supplies energy to the laser medium. 
A dye laser is an example of the liquid laser. A dye laser is a laser that uses an organic dye (liquid solution) as the laser medium. 
A dye laser is made up of an organic dye mixed with a solvent. These lasers generate laser light from the excited energy states of organic dyes dissolved in liquid solvents. It produces laser light beam in the near ultraviolet (UV) to the near infrared (IR) region of the spectrum.
Types of lasers
Semiconductor laser
Semiconductor lasers play an important role in our everyday life. These lasers are very cheap, compact size and consume low power. Semiconductor lasers are also known as laser diodes.
Semiconductor lasers are different from solid-state lasers. In solid-state lasers, light energy is used as the pump source whereas, in semiconductor lasers, electrical energy is used as the pump source.
In semiconductor lasers, a p-n junction of a semiconductor diode forms the active medium or laser medium. The optical gain is produced within the semiconductor material.
Laser in electromagnetic spectrum
The term "laser light" refers to a much broader range of the electromagnetic spectrum that just the visible spectrum, anything between 150nm up to 11000nm (i.e. from the UV up to the far IR).

Laser in electromagnetic spectrum 

Unique properties of laser (laser Vs light)
The laser has the following characteristics:
1- It is monochromatic. Only light of a single wavelength is produced in the whole process.
2- It is coherent. All photons have the same phase and the same polarization; hence they produce an very high intensity.
3- It has a very narrow and collimated ray, and hence it is very powerful. 



Laser power and classification of laser
Light intensity can be expressed in terms of power, measured in watts or milliwatts, or power density, measured in milliwatts per centimeter squared (mW/cm2 ).
 Power is the rate of energy flow, and power density is the amount of power per unit area. 
Laser and other light therapy applicators generally have a fixed power, although in some cases this can be reduced by pulsing the output. 
Because high-intensity lasers have the potential to cause harm, lasers have been divided into four classes, according to their power ranges  as in following table. 


Lecture 9: X-ray and radiation protection 
Ionization process.
Ionizing Vs non-ionizing radiation.
X-ray as a diagnostic tool.
Direct and indirect action of radiation.
Radio-sensitivity of the cell.

Structure of the atom: 
Q: What is the atom?
A: an atom is the core of every substance in the universe.

Q: What is the atom made of?
A: an atom is made of: 
Electrons (negative charge).                                  in the shell
Protons (positive charge) 
					           

            Quiz: