Why does the intensity of the torch light decrease with time?
a) From the battery electrons move through the circuit towards the light bulb. There, they burn up and so their light shines. As soon as the electrons of the battery are used up, the power of the lamp decreases.
b) The current transits the lamp with a specific strength. If the separation of charge is reduced in the battery thereby, the strength of current decreases and the intensity of the light bulb is weaker.
c) Because of the glow of the light bulb, the current strength of the batteries is constantly used up. The lower the current, the weaker the intensity of the light bulb.
d) Electric current is stored in the batteries by chemistry. By switching on the lamp, this current flows to the lamp and is used up there. If most of the current is used up, the lamp will only shine very weakly.