Q.State what is meant by saying that a physical law is “universal in nature”. Illustrate your answer with one example from mechanics and one from electromagnetism.

[!TLDR] A universal physical law holds unchanged at every place and every time, for every observer. [!ANSWER] Newton's law of gravitation $F = G\dfrac{m_1m_2}{r^2}$ (mechanics) and Coulomb's law $F = k\dfrac{q_1q_2}{r^2}$ (electromagnetism) are both universal — the same law applies whether the interacting bodies are on a laboratory bench or in a distant galaxy.

A physical law is called universal when it is expected to hold at every place in the universe and at every instant of time, for every properly accounted-for observer — it is not a locally observed regularity but a statement believed to describe nature itself.

Mechanics example. Newton's law of gravitation, $F = G\dfrac{m_1m_2}{r^2}$, was first checked using falling objects and the Moon's orbit around the Earth. The same law, with the same constant $G$, correctly predicts the orbits of planets around the Sun and of exoplanets around stars thousands of light-years away — nowhere does the law need a different constant or a different form depending on location.

Electromagnetism example. Coulomb's law, $F = k\dfrac{q_1q_2}{r^2}$, governing the force between two point electric charges, has the identical inverse-square mathematical form as gravitation, and is verified to hold with the same constant $k$ in every laboratory on Earth and in astrophysical environments studied through radiation from distant objects.

[!ANSWER] Both Newton's law of gravitation and Coulomb's law are universal: the same equation, with the same constant, governs the interaction everywhere in the universe and at every time — this universality is exactly what elevates an observed pattern to the status of a physical law.

Recall the defining property of a physical law — invariance across space, time and observer — then identify one mechanical and one electromagnetic law that both display this invariance.

• Confusing a 'universal' law with a law that has no exceptions under any condition (a law can be universal within its domain of validity and still be refined later, as gravitation was by general relativity)
• Giving an example that is actually a local rule of thumb (e.g. an empirical engineering formula) rather than a fundamental law