### Kepler's three laws of planetary motion

- The path of the planets about the sun is elliptical in shape, with the center of the sun being located at one focus. (The Law of Ellipses)
- An imaginary line drawn from the center of the sun to the center of the planet will sweep out equal areas in equal intervals of time. (The Law of Equal Areas)
- The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun. (The Law of Harmonies)

Published by German astronomer **Johannes Kepler** between 1609 - 1619.

### Lambert's Law (Luminous intensity)

It states that the luminous intensity of a perfectly diffusing surface in any direction is proportional to the cosine of the angle between that direction and the normal to the surface, for which reason the surface will appear equally bright from all directions.

Published by **Johann Heinrich Lambert,** a Swiss physicist in 1760.

### Lenz's Law (Electromagnetism)

It states that an induced electric current flows in a direction such that the current opposes the change that induced it or in other words an induced current is always in such a direction as to oppose the motion or change causing it.

Deduced in 1834 by the Russian physicist **Heinrich Friedrich Emil Lenz.**

### Newton's Law of motion

- Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.
- The acceleration of an object depends directly upon the net force acting upon the object, and inversely upon the mass of the object. As the force acting upon an object is increased, the acceleration of the object is increased. As the mass of an object is increased, the acceleration of the object is decreased.
- For every action there is an equal and opposite reaction.

Published by British physicist **Sir Isaac Newton** in 1687.

### Ohm's Law (Electricity)

Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points, and inversely proportional to the resistance between them.

Published in 1827 by German physicist **Georg Ohm.**

### Snell's Law (Refraction of light)

It states that the ratio of the sines of the angles of incidence and refraction is equivalent to the ratio of phase velocities in the two media, or equivalent to the opposite ratio of the indices of refraction.

Named after Dutch astronomer **Willebrord Snellius** who rediscovered it in 1621.