across the given wire, the electrons in the closed circuit resulting the current. Battery sets the potential difference (electrical energy) due to which these electrons in the conducting wire flow in a particular direction. The resulting electrical energy is used by electric bulb, electric fan etc. Similarly the electricity board is supplying the electrical energy to our home.
(ii) We often use the phrases like ‘charging the battery in my mobile’ and ‘my mobile phone battery has no charge’ etc. These sentences are not correct. it is subjected to an electric field. The average time between two successive collisions is called the mean free time denoted by τ.
The acceleration a experienced by the electron in an electric field E is given by a eE eE = − =− since ( . ) The drift velocity v d is given by v d a τ v d e m E =− τ ( . ) v d =− µ ( . ) Here µ τ = e m is the mobility of the electron and it is defined as the magnitude of the drift velocity per unit electric field.
µ = v d E ( . ) The SI unit of mobility is m V s - . The typical drift velocity of electrons in the wire is – m s – . If an electron drifts with this speed, then the electrons leaving the battery will take hours to reach the light bulb.
Then how electric bulbs glow as soon as we switch on the battery? When battery is switched on, the electrons begin to move away from the negative terminal of the battery and this electron exerts force on the nearby electrons. This process creates a propagating influence (electric field) that travels through the wire at the speed of light. In other words, the energy is transported from the battery to bulb at the speed of light through propagating influence (electric field).
Due to this reason, the bulb glows as soon as the battery is switched on. Note 12th - 12th - - -