Which component prevents current from flowing through a circuit when opened?

Which component prevents current from flowing through a circuit when opened?

• A. Open Switch
• B. Resistor
• C. Thermistor
• D. Transformer

Answer: (A)

Current can flow only when there is a closed path for the current to travel. Opening the switch breaks the circuit, turning it into an open circuit. With the path interrupted, the resistance seen by the source becomes effectively infinite, so the current drops to zero according to Ohm’s law. A resistor, by contrast, simply slows current but doesn’t automatically break the circuit; it still relies on a complete loop to allow current to flow. A thermistor changes its resistance with temperature, not by intentionally opening the circuit, so it doesn’t guarantee zero current. A transformer requires a closed electrical path to function; if the circuit is opened, no current can flow through it. Thus, an open switch is the component that prevents current from flowing when opened.

Current can flow only when there is a closed path for the current to travel. Opening the switch breaks the circuit, turning it into an open circuit. With the path interrupted, the resistance seen by the source becomes effectively infinite, so the current drops to zero according to Ohm’s law. A resistor, by contrast, simply slows current but doesn’t automatically break the circuit; it still relies on a complete loop to allow current to flow. A thermistor changes its resistance with temperature, not by intentionally opening the circuit, so it doesn’t guarantee zero current. A transformer requires a closed electrical path to function; if the circuit is opened, no current can flow through it. Thus, an open switch is the component that prevents current from flowing when opened.