Glossary
diode
A diode is a semiconductor one-way valve: current passes in one direction only, and its symbol is a triangle pointing into a bar.
A diode is a one-way valve for current. It is made of semiconductor material joined so that charge crosses it easily in one direction and not at all in the other, and its symbol is a triangle pointing into a bar — the direction the triangle points is the direction current passes. Flip the supply and the diode blocks.
That one property does the work of three answers. A rectifier uses diodes to turn alternating current into direct current; a diode across a relay coil absorbs the voltage spike when the coil switches off; and an LED is the same one-way junction with a case built so that the energy given off appears as light rather than heat.
Read the symbol to answer most diode questions. Current leaves the triangle and stops at the bar, so the bar is the blocked end. Test it with a meter and it shows continuity one way and open the other, unlike a resistor, which resists in both directions, or a capacitor, whose plates never touch at all.
Taught in
Related terms
- capacitor — A capacitor is a component of two plates separated by an insulator that stores charge and gives it back, so it blocks steady current and passes a changing signal.
Source: Official ASVAB — subtest descriptions (what each subtest asks) and the CAT-ASVAB scored-question counts (accessed 2026-09)