Question

in the parallel circuit pictured, what happens if lightbulb a burns out?
lightbulb c gets brighter.
all of the bulbs go out.
only lightbulb a turns off.

Explanation:

In a parallel circuit, each component has its own separate path for current. So, if one component (like bulb B here) fails (burns out), it doesn't affect the other components. The voltage across each component in parallel is the same as the source voltage (assuming ideal conditions), and the current through each branch is determined by \(I=\frac{V}{R}\) (Ohm's law, where \(V\) is voltage and \(R\) is resistance of the component). Since bulb A and bulb C are in separate branches from bulb B, bulb A will not be affected by bulb B burning - out.

Answer:

Only lightbulb A turns off.