Which device permits current to flow in only one direction?

Which device permits current to flow in only one direction?

• A. Capacitor
• B. Resistor
• C. Diode
• D. Transistor

Answer: (C)

A diode made of a PN junction behaves like a one-way gate for electricity. When the anode is more positive than the cathode by enough voltage (forward bias), the junction’s barrier disappears enough for charge carriers to cross, so current flows. If the polarity reverses (reverse bias), the depletion region widens and blocks most current, so the flow is prevented. That combination—conducting in forward direction and blocking in reverse—gives it the single-direction behavior. Think of it like a one-way valve for electrons and holes. This is why diodes are used in rectifiers to convert alternating current to direct current. Capacitors store energy in an electric field and can pass current only during changes in voltage; they don’t enforce a single direction of current flow. Resistors simply resist current according to Ohm’s law and don’t force a direction. Transistors act as switches or amplifiers controlled by a gate/base signal and can control whether current flows in a circuit, but they aren’t inherently one-way conduits in the same way a diode is.

A diode made of a PN junction behaves like a one-way gate for electricity. When the anode is more positive than the cathode by enough voltage (forward bias), the junction’s barrier disappears enough for charge carriers to cross, so current flows. If the polarity reverses (reverse bias), the depletion region widens and blocks most current, so the flow is prevented. That combination—conducting in forward direction and blocking in reverse—gives it the single-direction behavior.

Think of it like a one-way valve for electrons and holes. This is why diodes are used in rectifiers to convert alternating current to direct current.

Capacitors store energy in an electric field and can pass current only during changes in voltage; they don’t enforce a single direction of current flow. Resistors simply resist current according to Ohm’s law and don’t force a direction. Transistors act as switches or amplifiers controlled by a gate/base signal and can control whether current flows in a circuit, but they aren’t inherently one-way conduits in the same way a diode is.