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This famous two-letter equation, published in 1905, demonstrates that a small amount of matter contains enormous amounts of energy.
Difficulty: EasyThis phenomenon explains why electrons are ejected from metals when light of sufficient frequency shines on them.
Difficulty: MediumThis type of constraint can be expressed as equations involving only coordinates, not velocities, such as a pendulum's fixed length.
Difficulty: HardThis invisible force field surrounds every magnet and allows it to attract iron objects without touching them.
Difficulty: EasyThis French chemist developed the germ theory of disease, created vaccines for rabies and anthrax, and invented a heat treatment to make beverages safer.
Difficulty: MediumThis parameter in black hole thermodynamics equals one quarter of the event horizon area in Planck units, first derived by combining quantum mechanics with relativity.
Difficulty: HardAccording to legend, a falling apple inspired this scientist to develop his theory of gravity in the 1680s.
Difficulty: EasyThis country served as the birthplace and lifelong home of the physicist who revolutionized our understanding of motion and light.
Difficulty: Medium