Identify the force present and explain whether work is done when (a) an electron moves in a circle at a fixed distance from a proton, (b) an iron nail is attracted by and pulled onto a magnet.

Verified step by step guidance

1. Step 1: Identify the forces involved in each scenario. For (a), consider the electrostatic force between the electron and the proton. For (b), consider the magnetic force between the iron nail and the magnet.
2. Step 2: For scenario (a), recognize that the electron is moving in a circular path around the proton. The electrostatic force acts as the centripetal force, keeping the electron in its circular orbit.
3. Step 3: Determine if work is done in scenario (a). Recall that work is done when a force causes displacement in the direction of the force. Since the electron moves perpendicular to the electrostatic force (which acts radially), no work is done.
4. Step 4: For scenario (b), the iron nail is initially at rest and then moves towards the magnet. The magnetic force does work on the nail as it moves in the direction of the force.
5. Step 5: Conclude that in scenario (a), no work is done because the force is perpendicular to the motion. In scenario (b), work is done because the force causes displacement in the direction of the force.

Key Concepts

Centripetal Force

Centripetal force is the net force acting on an object moving in a circular path, directed towards the center of the circle. In the case of an electron moving in a circle around a proton, the electrostatic attraction between the negatively charged electron and the positively charged proton provides the necessary centripetal force to maintain the circular motion.

Work Done by a Force

Work is defined as the product of the force applied to an object and the displacement of that object in the direction of the force. If the force is perpendicular to the displacement, as in the case of an electron moving in a circle, no work is done. Conversely, when an iron nail is attracted to a magnet, work is done as the nail moves towards the magnet, resulting in a displacement in the direction of the magnetic force.

Electromagnetic Forces

Electromagnetic forces are one of the four fundamental forces of nature, arising from the interaction between charged particles. In the context of the question, the attraction between the electron and proton is due to electromagnetic forces, while the attraction between the iron nail and the magnet is also a manifestation of these forces, specifically the magnetic component acting on ferromagnetic materials.