Electromagnetism · Explainer
Why magnetic force does no work—even in a moving rod
A moving conductor can power a circuit without the magnetic force doing work on its charges. The key is to include both the rod’s motion and the charge’s drift.
The reading room
Physics, understood.
Explanations that begin with a question and follow the reasoning wherever it leads.
Cosmology · Explainer
Light carries the history of the universe.
From the stars next door to distant galaxies, every observation begins with a journey through time.
Quantum Physics · Explainer
What does a quantum state actually tell us?
Start with the predictions of the theory, and separate what can be measured from what must be interpreted.
Relativity · Explainer
The time a clock actually measures.
Proper time begins with one clock, two events, and the path that connects them.
Electromagnetism · Explainer
How can a field carry energy?
A field is more than a set of arrows. Changing electric and magnetic fields can transport energy through space.