IB Physics

Dark lines in a stellar spectrum at specific wavelengths where photons have been absorbed by atoms in the star's outer atmosphere. Each element produces a unique set of lines, allowing astronomers to identify the chemical composition of a star.

Absorption spectrum is the range of frequencies of electromagnetic radiation readily absorbed by a substance by virtue of its chemical composition.

Acceleration is the rate of change of velocity.

The activity of a radioactive sample is the number of decays per unit time.

Air drag is a resistive force that acts on objects moving through air.

Alpha decay occurs when an unstable nucleus emits an alpha particle, which is essentially a helium nucleus made up of two protons and two neutrons ($^4_2 \text{He}$).

Alternators are devices that convert mechanical energy into electrical energy using the principles of electromagnetic induction.

Amplitude is the maximum displacement of an oscillating object from its equilibrium position.

Angular acceleration is the rate of change of angular velocity.

Angular displacement is the angle through which an object moves on a circular path. It is measured in radians.

Angular frequency $\omega$ is the rate of change of phase of an oscillation, equal to $2\pi f$ and measured in radians per second (rad s$^{-1}$).

Angular impulse is a concept in rotational motion that describes the change in angular momentum of a rigid body due to the application of torque over a period of time.

Angular momentum is the rotational equivalent of linear momentum. More precisely, it is the product of its moment of inertia and its angular velocity.

Angular velocity ($\omega$) is the rate of change of angular displacement. It is measured in radians per second (rad/s).

Antinodes are points on a standing wave where the displacement reaches its maximum value.

Apparent brightness is a measure of how bright an object appears to an observer. It depends on both the intrinsic luminosity $L$ of the object and its distance $d$ from the observer.

Atmospheric drag is the resistance experienced by an object moving through a planet’s atmosphere.

Average speed is the total distance traveled divided by the total time taken. It’s a scalar quantity.

Average velocity is the total displacement divided by the total time taken. It’s a vector quantity.

In beta minus decay, a neutron in the nucleus is converted into a proton, emitting an electron ($\beta^-$) and an antineutrino ($\bar{\nu}$):

$$
n \rightarrow p + e^- + \bar{\nu}
$$

In beta plus decay, a proton is converted into a neutron, emitting a positron ($\beta^+$) and a neutrino($\nu$):

$$
p \rightarrow n + e^+ + \nu
$$

Binding energy is the energy required to hold the nucleus together.

A black body is an idealized object that absorbs all radiation falling on it and emits radiation based on its temperature.

A region of spacetime where gravity is so strong that nothing, not even light, can escape from within its event horizon. Formed when the remnant core of a massive star exceeds about 3 solar masses (the Oppenheimer-Volkoff limit).