Final answer:
Filaments in cathode ray tubes and light bulbs are made of tungsten, which is selected for its ability to emit a white light when heated. Tungsten is preferable over other metals like copper, iron, or aluminum for this purpose.
So, the correct answer is: Tungsten
Step-by-step explanation:
The filaments in the cathode ray tube (CRT) and electric light bulbs are composed of tungsten. This choice is due to tungsten's ability to emit light that contains virtually every frequency, resulting in a white light when the filament is heated. Other materials may not emit the desired white light and therefore are not as suitable for these applications.
In cathode ray tubes, such as those used in older television screens and X-ray machines, a filament voltage is applied to heat the tungsten filament. This generates electrons that are then accelerated towards a copper anode, producing X-rays upon impact. Similarly, in light bulbs, when an electric current is passed through the tungsten filament, it becomes hot enough to glow, thus generating light.
Other metals like copper, iron, or aluminum are not commonly used for filaments because they do not have the same properties as tungsten in terms of melting point and light emission.