The electric current is carried by moving electric charges (free electrons in metals) driven by external electric field (potential difference). The strength of the current depends on
- Number of free electrons in bulk motion
- Speed of the bulk motion (typically some cms in an hour)
- Collisions between the atoms in thermal motion
Due to the collisions, electrons loose kinetic energy i.e. electrical energy is transformed thermal energy (power dissipation). To maintain the current, work needs to be done at the same rate inside the power supply (cell, battery etc).
The lamp illuminates in five of the following cases. Which?
