A charged battery contains electrons that want to flow from the negative to positive terminal. For a light bulb to turn on, there must be a complete circuit for the electrons to flow through. Simply connecting wires to the battery and bulb is not enough, as the electrons will take the easiest path without going through the bulb's filament. The bulb is designed so that the only way for electrons to travel from the base to the contact is by flowing through the filament, causing it to light up. When wires create a complete circuit with the battery, base, and contact, current will pass through the filament, turning on the bulb.

1. Light bulb and battery Inside a

2. A charged battery is kind of like a bucket full of electrons.

3. The electrons only want to race from the bottom (negative terminal) to the top (positive terminal). They will do work on the way, but only if they have to. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Flow of electrons Negative terminal Positive terminal + + + + +

4. But there must be a complete circuit or no electrons can flow. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Flow of electrons Negative terminal Positive terminal A gap in the circuit stops the flow of electrons.

5. This won’t light up the bulb because there isn’t a complete circuit. Electric current must have a circuit. It must get back to where it started.

6. Now there is a circuit, but it still won’t light up the bulb. Electric current is flowing, but it’s not going through the bulb.

7. Current will always go the easiest way. is flowing, but it’s not going through the bulb. This current can get back to the battery without going through the filament.

8. Current will go the easiest way. is flowing, but it’s not going through the bulb. It won’t go through the bulb unless it has to. Flow of electric current

9. The bulb will only light up if the current flows through the filament. filament

10. The bulb is designed with one wire connecting the filament with the base and the other side of the filament connected to the contact on the bottom. Blue wire connects filament to base. Green wire connects filament to contact.

11. The bottom of the bulb shows the contact and base being separated by a black ring of insulator material. Current can’t flow through the insulator so it must flow through the filament to get from the base to the contact. base insulator contact

12. One wire must touch the base and the other wire must touch the contact Base Contact

13. Current can’t flow through the insulator so it must flow through the filament to get from the base to the contact. Wire coming from bottom of the battery Wire going back to the top of the battery. Flow of electric current

14. Now the current must go through the filament to get back to the battery. is flowing, but it’s not going through the bulb.

15. Now there is a circuit, and the bulb is on. Electric current is flowing through the filament.