Final answer:
The brightness of a light bulb decreases as its resistance increases when connected to a constant voltage source, due to less current flowing through the bulb, leading to less power dissipation. So the correct option is C.
Step-by-step explanation:
The brightness of a light bulb, often referred to as its luminosity, depends on the power it dissipates, which is related to the resistance in the bulb. According to Ohm's law, increasing the resistance while keeping the voltage constant results in a lower current through the bulb. This can be seen in the equation P = I2R, where P is the power, I is the current, and R is the resistance. If the voltage (V) is kept constant and resistance (R) is increased, the current (I) will decrease since I = V/R. Consequently, the power dissipated by the bulb which determines its brightness will decrease as less current flows through it. Therefore, the light bulb gets dimmer as the resistance is increased.