The filament of light bulb operates at 2000K it has a diameter of 0.80mm and is made of metal of emissivity 0.5. What is the length of filament is needed if the power of the ball is to be 100W. ( stefan's constant= 5.67×10^-8)​

Two large, flat, horizontally oriented plates are parallel to each other, a distance d apart. half way betwween the two plates the electric field has magnitude e. if the separation of the plates is reduced to d/2 what is the magnitude of the electric field half way between the plates?

The sun’s mass is 2.0×10^ 30 kg, its radius is 7.0×10 5 km, and it has a rotational period of approximately 28 days. if the sun should collapse into a white dwarf of radius 3.5×10 3 km, what would its period be if no mass were ejected and a sphere of uniform density can model the sun both before and after?

Holes drilled several kilometers into earth’s crust provide direct evidence about earth’s interior in the form of