What is the main function of a diode in an electrical circuit?

The primary function of a diode in an electrical circuit is to allow current to flow in one direction only. This characteristic is crucial in controlling the direction of electrical current, making diodes essential components in various applications such as rectification, where alternating current (AC) is converted to direct current (DC).

When a diode is forward-biased, it conducts electricity, allowing current to pass through it. Conversely, when it is reverse-biased, the diode blocks current flow, preventing it from passing in the opposite direction. This unidirectional property is what makes diodes so valuable for protecting circuits from reverse polarity and ensuring that current flows where it is intended.

The other options involve different functions that diodes do not perform. Measuring voltage requires a different component, such as a voltmeter. Allowing current to flow in two directions is the function of devices like bridges or certain types of switches, but not diodes. Voltage spikes are managed by devices specifically designed for that purpose, such as surge protectors or varistors, rather than standard diodes.