Final answer:
Adding a light bulb to a circuit could make all bulbs dimmer if connected in series or have no effect if connected in parallel, in ideal conditions.
Step-by-step explanation:
If another light bulb is added to a circuit, the effect on the brightness of the existing light bulbs depends on how the new bulb is added. If the light bulbs are connected in series, the total resistance of the circuit increases, causing the overall current to decrease, which in turn would make all bulbs dimmer. The correct answer is b) The light bulbs would get dimmer. If the bulbs are connected in parallel, the overall resistance of the circuit decreases, allowing more current to flow through each individual branch; however, the addition of another parallel branch with a bulb could either have no effect or potentially reduce the brightness of the others slightly due to the voltage drops that occur in real circuits, depending on how the power supply reacts to the increased load. Nonetheless, for ideal cases, adding a bulb in parallel is expected to have no effect on the brightness of the other bulbs. So, the answer could be d) No effect on the brightness of the light bulbs for parallel circuits.