Answer
Because there are already electrons in the wires inside of the flashlight; the electrons do not only start at the source of power. Flipping on the switch completes the circuit causing electrons to flow into lightbulb. Again, since there are already electrons in the wire, turning on the switch just sends the closest electron in the wire to the lightbulb in the flashlight to produce light.
Work Step by Step
Because there are already electrons in the wires inside of the flashlight; the electrons do not only start at the source of power. Flipping on the switch completes the circuit causing electrons to flow into lightbulb. Again, since there are already electrons in the wire, turning on the switch just sends the closest electron in the wire to the lightbulb in the flashlight to produce light.
