A Level Physics Practice Exam

How are electrons held in an atom?

1. By magnetic forces

2. By the gravitational force of the nucleus

3. By the electrostatic force of attraction

4. By mass attraction

The correct answer is: By the electrostatic force of attraction

Electrons are held in an atom primarily by the electrostatic force of attraction between the negatively charged electrons and the positively charged protons in the nucleus. According to Coulomb's law, opposite charges attract; therefore, the negatively charged electrons are drawn toward the positively charged nucleus. This electrostatic interaction is fundamental to the structure of an atom, creating a balance between the attractive forces of the nucleus and the kinetic energy of the electrons, which allows them to occupy specific energy levels or orbitals around the nucleus. While magnetic forces can act on moving charges, they are not relevant to the fundamental structure of the atom as described in this context. Gravitational forces, although present, are extremely weak compared to the electrostatic forces in play at the atomic scale, rendering them negligible in influencing the binding of electrons. Similarly, mass attraction typically refers to gravitational interactions and is not a relevant factor in the atomic structure. Hence, the dominant mechanism keeping electrons in their respective orbits around the nucleus is indeed the electrostatic force of attraction.