Engine 2014: Electricity

1. A A vacuum tube requires a heated cathode to emit electrons, a semiconductor device does not.
2. B A semiconductor device requires a heated cathode to emit electrons, a vacuum tube does not.
3. C Both vacuum tubes and semiconductor devices require a heated cathode to emit electrons.
4. D Neither vacuum tubes nor semiconductor devices require a heated cathode to emit electrons.

Tip: press A-D to answer