LAMPS

==Lamps or Filament (bulb)== An incandescent light bulb with a tungsten filament has a positive temperature coefficient, and therefore has a very low initial resistance when the power is first applied. As the temperature of the filament increases, the resistance of the filament increases also. The temperature of the resistor increases by increasing the applied voltage, since the power dissipated as heat is increased due to the relation P = IV , where I is the current passing through the tungsten filament and V is the voltage applied across it. For metals, the number of free electrons is fixed. As the temperature increases, the amplitude of vibration of atoms/ions increases and collisions of electrons with them become more effective and frequent. As a result, current carrying electrons find more resistance in passing through and the resistance increases. The image below shows the voltage and current relation of a tungsten filament. From the figure, it is clear that the resistance of the filament increases with applied voltage and the filament has a dynamic resistance. The resistance at A and B can be found by using R = V/I relation at that particular points and you can prove that RB > RA. [image:http://i.imgur.com/uZJQtMR.png]