🔍 Key Concepts

• How electrons are typically released from a heated metal surface in classic radio‑type vacuum tubes • The meaning of the prefix "thermo" and how it relates to heat in physical processes • The difference between light-caused emission and heat-caused emission of electrons

💭 Think About

• Ask yourself: in most common vacuum tubes used in electronics, is the cathode usually heated or left cold? • Which option’s name directly suggests the use of heat to free electrons from a metal? • Which other options describe special or less common effects, such as emission caused by light or by electrons striking a surface?

✅ Before You Answer

• Identify which choice specifically refers to heat‑driven electron emission. • Eliminate any answer that clearly involves light (photons) instead of heat. • Consider which process is described in basic radio and electronics texts as the standard way cathodes in vacuum tubes emit electrons.