The scenario that will cause the current to stop flowing within a circuit is option C: the switch within the closed circuit is opened.
Here's an explanation of each scenario and why option C is the correct answer:
a) Insulating materials within the circuit are replaced with conducting materials:
This scenario will not cause the current to stop flowing. Conducting materials allow the flow of electric current, so replacing insulating materials with conducting materials will actually enhance the flow of current in the circuit.
b) A wire connected to the voltage source runs from the negative to the positive terminal:
In a circuit, the flow of current is from the positive terminal to the negative terminal of the voltage source. So, if a wire is connected from the negative to the positive terminal, it will not stop the current flow. The current will still flow in the circuit, but in the opposite direction.
c) The switch within the closed circuit is opened:
When the switch within a closed circuit is opened, it breaks the continuity of the circuit, causing an air gap or break in the current path. As a result, the flow of current will stop because there is no complete path for it to follow.
d) The circuit is closed:
Closing the circuit means completing the path for the electric current to flow. When the circuit is closed, the current can freely move through the circuit and continue flowing.
Therefore, the correct answer is option C: the switch within the closed circuit is opened. Opening the switch interrupts the flow of current and stops it from moving through the circuit.