- Question 2 Imagine That You Are Designing An Incandescent Lightbulb This Will Consist Of A Tungsten Filament Inside A 1 (224.81 KiB) Viewed 123 times
Question 2 Imagine that you are designing an incandescent lightbulb. This will consist of a tungsten filament, inside a glass bulb. The air pumped out of the bulb, so the tungsten filament is in a vacuum. The tungsten filament is a cylindrical wire 2.5m long and 0.03 mm in radius. It is wound into a helix so it can fit in the bulb. This filament has a resistance of 707 ohms at its operating temperature. The bulb can be approximated as a sphere of radius 2.3 cm. It is made of glass, with a thickness of 2.4mm. Tungsten has a density of 19300 kg m-³, a melting point of 3410C, a specific heat capacity of 134 J kg-1 kg¹, and a thermal conductivity of 120 W m³¹ K-¹. The glass used in this bulb has a density of 2600 kg m³, a specific heat capacity of 840 J kg-¹ K-¹ and a thermal conductivity of 0.8 W m1 K-1. A) If a voltage of 120V is applied to the filament, how hot will it get? Will it melt? Carefully explain your reasoning. (10 marks) B) When the power is first turned on, approximately how long will it take before the bulb is at full brightness? Sketch a graph of how the temperature will vary as a function of time. Carefully explain your reasoning. (5 marks)