How do all these flashlight parts work together?
When the switch of a flashlight is pushed into the ON position, it makes contact between two contact strips, which begin a flow of electricity, powered from the battery. The batteries are connected in such a way that electricity (flow of electrons) runs between the positive and negative electrodes of the battery. The batteries rest atop a small spring that is connected to a contact strip. The contact strip runs down the length of the battery case and makes contact with one side of the switch. There is another flat contact strip on the other side of the switch, which runs to the lamp (light bulb), providing an electrical connection. There is another part connected to the lamp that makes contact with the positive electrode of the top battery, thus completing the circuit to the lamp and completing the generation of electricity.
When activated by electricity, the tungsten filament or LED in the lamp begins to glow, producing light that is visible. This light reflects off of the reflector that is positioned around the lamp. The reflector redirects the light rays from the lamp, creating a steady beam of light, which is the light you see emitting from the flashlight. A clear lens covers the lamp on your flashlight so that the glass on the lamp does not get broken.
When the flashlight switch is then pushed into the OFF position, the two contact strips are physically moved apart and the path for the electrical current is broken, thus ending the production of light, and turning your flashlight off.
All of the above parts must be connected and in place in order for the portable flashlight to work. Otherwise, you have an open circuit and the electricity will not flow.