Final answer:
The value of current decreases as more light bulbs are added in series due to increased resistance. For parallel circuits, the current can remain the same through each branch. Incandescent bulbs dim over time due to an increase in filament resistance, reducing current.
Step-by-step explanation:
When more light bulbs are added to a circuit, the total resistance of the circuit increases if the bulbs are connected in series, and as a result, the value of current decreases. According to Ohm's law, current (I) is the result of the voltage (V) divided by resistance (R), I = V/R. Thus, in a series circuit, where the resistance sums up, adding more bulbs (which act as resistors) increases the circuit's total resistance and decreases the current. However, if the bulbs are arranged in parallel, the addition of more bulbs reduces the total resistance of the circuit, and the current through each branch can remain the same.
In discussions of electric power and energy, the relationship between voltage, current, and resistance is encapsulated by the formula P = I^2 * R, whereby power (P) is proportional to the square of the current times the resistance. For incandescent light bulbs, over time the filament can deteriorate, resulting in increased resistance; this causes the current and hence the brightness to reduce just before the filament breaks. The heat generated (and light emitted) by incandescent bulbs comes from the electrical energy transferred to the filament, converted into light and thermal energy because of its resistance.