If R2 sticks in the up position, the light will

• A. be very dim.
• B. not illuminate.
• C. be on full bright.
• D. flicker.

Answer: (C)

Light brightness is determined by how much current flows through the lamp. When R2 is in the up position, the current path to the lamp is completed in a way that bypasses the extra resistance that would limit current. That means the lamp gets the full supply voltage, the current is at its maximum for this circuit, and the lamp shines at full brightness. If the switch were in the other position, the current would have to pass through the resistor path, reducing current and making the light dimmer or off. Remember, the lamp’s brightness also changes a bit as its resistance changes with temperature, but the principle remains: the up position gives the most current and thus full brightness.