The photograph shows a filament bulb.
The filament is an emitter with 35% of the power output of a black body radiator of the same temperature.
surface area of filament = 3.9 × 10−6 m2
Temperature = ....................................................................
When a small p.d. is applied to the bulb, no light is visible. If the p.d. is gradually increased, the filament starts to glow and eventually appears white.
Your answer should include a calculation.
(5)
(2)
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