1,800+ MCAT terms, defined.

The incident angle is the angle between an incoming ray and the normal, the line perpendicular to the surface at the point where the ray hits. It is measured from the normal, not from the surface. It equals the reflected angle and, throu...

Partial interference happens when two overlapping waves are neither exactly in phase nor exactly out of phase, so the resultant amplitude falls between the fully destructive and fully constructive values. Full cases need a path differenc...

Complementary colors are two colors of light that add together to make white, such as red and cyan, green and magenta, or blue and yellow. Testable point: a pigment or filter that absorbs one color from white light typically appears as t...

Drag is the resisting force a fluid (liquid or gas) exerts on an object moving through it, pointing opposite the object's velocity relative to the fluid. It increases with speed, so a falling object reaches terminal velocity when drag pl...

The work-energy principle says the net work done on an object by all the forces acting on it equals its change in kinetic energy. Positive net work speeds the object up, and negative net work slows it down. The work of one force alone is...

A decibel (dB) is a logarithmic unit for sound intensity level, comparing an intensity to the hearing threshold I₀ = 1.0 × 10⁻¹² W/m². The key point: every +10 dB means intensity is multiplied by 10, and +3 dB roughly doubles it.

Electric force is the push or pull between charged objects: like charges repel and opposite charges attract. Its size follows Coulomb's law, proportional to the product of the charges and inversely proportional to the square of their sep...

The magnification equation, m = −i/o = hᵢ/hₒ, gives the ratio of image size to object size for a mirror or lens. The sign shows orientation: for a real object, negative m is an inverted, real image and positive m is an upright, virtual i...

A concave (diverging) lens is thinner at its center than its edges and spreads parallel rays apart. It has a negative focal length and, for a real object, always forms a virtual, upright, reduced image on the same side as the object.

A converging (convex) lens is thicker at the center and, in a lower-index medium such as air, bends parallel rays to a focal point; f is positive. It forms a real, inverted image when the object is beyond f, but a virtual, upright, enlar...

Young's double-slit experiment sends coherent light through two narrow slits. The overlapping waves form alternating bright and dark fringes on a screen, which is evidence that light is a wave. Bright fringes occur where the path differe...

Ferromagnetic materials (iron, cobalt, nickel) contain domains of aligned atomic magnetic moments, so they are strongly attracted to magnets and can stay magnetized after the field is removed. Paramagnetic materials are only weakly attra...