D-unit IB physics 2025

Field

A region of space where a force acts.

Newton's universal law of gravitation

Every single point mass attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of their separation.

Gravitational force

The attractive force between objects with mass. It is directly proportional to the product of the masses, and indirectly proportional to the square of their separation.

Gravitational field strength

The (gravitational) force per unit mass experienced by a small point mass placed in the field.

Gravitational potential

The work done per unit mass taking a mass from a position of zero potential to the point P.

Gravitational potential energy

The work done when bringing a test mass from infinity to a point in space with low constant speed. This equals the potential energy per unit mass.

Kepler's first law

Planetary orbits are elliptical with a star at a focus.

Kepler's second law

The radius vector from the star to the orbiting body sweeps equal areas in equal times.

Kepler's third law

The square of the orbital period is proportional to the cube of the semi-major axis of the ellipse.

Charge

(Electric) charge is a physical property of matter that causes it to experience a force when placed in an electric field.

Fundamental charge

The smallest possible amount of charge. This equals the charge of an electron, e, or of a proton (but with opposite sign).

Electric field strength

The force per unit charge experienced by a small positive test charge placed at that point.

Relative permittivity

The ratio of its permittivity to the permittivity of a vacuum. Permittivity is different for different media.

Coulomb's Law (electric force)

The force experienced by two point charges is directly proportional to the product of their charge and inversely proportional to the square of their separation.

Electrical potential energy

Amount of work done in bringing a positive test charge from infinity to a point.

Electric potential

The amount of work done per unit charge in taking a small positive test charge, q, from infinity and putting it on a charged sphere.

Potential difference

Difference in potential between two points.

Electronvolt

Unit for Volt per electron. 1 eV = energy gained by an electron accelerated through a potential difference of 1 V.

Magnetic flux density, B

Density of magnetic field lines. This is the quantity used to measure the strength of magnetic fields.

Millikan's oil drop experiment

Millikan allowed charged small oil droplets to travel through a hole into an electric field in the experiment. With the electric field's varying strength, the charge over an oil droplet is calculated, and it always comes as a fundamental value of 'e.'

Faraday's Law

The magnitude of the induced emf is equal to the rate of change of flux.

Lenz's Law

The direction of the induced current is such that it will oppose the change producing it.

Induced emf

Electromagnetic Induction is a current produced because of voltage production (electromotive force) due to a changing magnetic field.