[填空题]
The graph shows the variation of current with voltage of a filament.
This filament is used in a light bulb, and it is made of a long tungsten wire that is wound several times. The filament is heated up when current flows and produces light.
The following data are available for the filament.
The diameter of tungsten wire6.0μm
The resistivity of tungsten when it produces light=2.0μΩcm
1.State Ohm’s law.
2.The filament's normal operation in a light bulb is at a potential difference of 6.0V.
(1)Show that the resistance of the filament at a potential difference of 6.0V is 120Ω.R= Ω
(2)Calculate the length of the filament.L= m
The light bulb is connected to a $100.0\,Ω$ resistor and a cell with emf ϵ and negligible internal resistance.
3.Calculate the required emf of the cell ϵ to operate the bulb at the normal conditions of the filament.ϵ= V
