Final answer:
Adding lightbulbs in parallel decreases the overall resistance and increases the current in a parallel circuit because each bulb adds an additional path for current to flow without increasing the voltage.
Step-by-step explanation:
When lightbulbs are added in a parallel circuit, the reason current increases and resistance decreases is because each lightbulb provides an additional path for the current to flow. This parallel arrangement means that the total resistance is the reciprocal of the sum of the reciprocals of the individual resistances, resulting in a lower overall resistance. Since resistance is inversely related to current (Ohm’s law: V=IR), as resistance decreases, the current through the circuit increases. This is because the voltage remains constant across each bulb and each additional path allows more current to flow through the circuit without an increase in voltage.
In high-current situations, a low resistance device when switched on allows a large current to flow, which can cause a larger voltage drop across the internal resistance of the wires (IR drop), resulting in lights dimming as they experience a reduced voltage. Therefore, it's important to note that while adding bulbs increases the overall current, it might also cause unintended voltage drops if the circuit's wiring has significant resistance.