B

　　Basis vector

　　A vector of magnitude 1 along one of the coordinate axes. Generally, we take the basis vectors to be and , the vectors of length 1 along the x- and y-axes, respectively.

　　Beats

　　When two waves of slightly different frequencies interfere with one another, they produce a “beating” interference pattern that alternates between constructive (in-phase) and destructive (out-of-phase). In the case of sound waves, this sort of interference makes a “wa-wa-wa” sound, and the frequency of the beats is equal to the difference in the frequencies of the two interfering waves.

　　Beta decay

　　A form of radioactive decay where a heavy element ejects a beta particle and a neutrino, becoming a lighter element in the process.

　　Beta particle

　　A particle, identical to an electron. Beta particles are ejected from an atom in the process of beta decay.

　　Bohr atomic model

　　A model for the atom developed in 1913 by Niels Bohr. According to this model, the electrons orbiting a nucleus can only orbit at certain particular radii. Excited electrons may jump to a more distant radii and then return to their ground state, emitting a photon in the process.

　　Boiling point

　　The temperature at which a material will change phase from liquid to gas or gas to liquid.

　　Boyle’s Law

　　For a gas held at a constant temperature, pressure and volume are inversely proportional.

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