| Neon Bulb: The neon bulb allows the user to determine the direction of current flow. Hence, it is the only object in the Static Electricity & Magnetism simulators that allows students to discern a difference between positive and negative charges, (other than their model colors). You can place one neon bulb. You must attach it to the electroscope (Electrostatic Lab Bench simulator), the electrophorus (Electrophorus simulator) or the Faraday pail (Faraday Pail simulator). The figures below demonstrate how you can use a neon bulb to determine the sign of the charge on a conductor. In both examples, the grounding hand is being used to discharge the conductor through a neon bulb. In Figure 1a, the conductor is negatively charged. As the conductor discharges, the left side of the neon bulb lights up (Figure 1b). The left side always lights up when electrons flow across the bulb to the right and current flows to the left.
Fig. 1a | Fig. 1b
Fig. 2a | Fig. 2b
In Figure 2a, the conductor is positively charged. As the conductor discharges, the right side of the bulb lights up (Figure 2b). The right side always lights up when electrons flow across the bulb to the left and current flows to the right.