🔍 Key Concepts

• Look closely at the wire filament shown in figure A compared to the discharge tubes shown in the other figures. • Notice the labels such as high internal gas pressure, support wires, and the absence or presence of a discharge tube or sodium/mercury vapor. • Think about which lamp types (mercury, sodium, or incandescent) typically use a filament as the primary light‑producing element.

💭 Think About

• Which of the four answer choices is the only lamp type that primarily produces light by heating a metal filament until it glows? • For each of the vapor or sodium lamps listed, do they normally show a long discharge tube instead of a simple coiled filament? • Does the construction shown in figure A more closely match a simple household bulb or the elongated, jacketed tubes in the other figures?

✅ Before You Answer

• Verify which option corresponds to a lamp that uses a coiled filament instead of an arc discharge tube. • Check whether high‑pressure mercury or sodium lamps generally contain mercury or sodium vapor and a distinct arc tube—do you see those labeled in figure A? • Confirm that the base and bulb shape in figure A match the most common, simple general-service lamp design you already know.