Summary
Highlights
Leptons are elementary particles, a Greek word meaning 'light' or 'to peel' (smaller). There are six leptons, arranged in three generations, mirroring quarks. The first and most familiar lepton is the electron, symbolized as e-, which has an electric charge of -1.
The electron neutrino (symbolized as a 'v' with an 'e' subscript) is a small, neutral particle that was predicted to account for the conservation of momentum in certain reactions. While originally thought mass-less, it possesses a tiny mass and travels just under the speed of light. Its charge is 0.
The second generation includes the muon (symbolized by the Greek letter mu, µ), a heavier, unstable particle similar to a fat electron, with an electric charge of -1. Its neutral counterpart is the muon neutrino (symbolized by 'v' with a 'µ' subscript), which has a charge of 0.
The third generation features the tau particle (symbolized by the Greek letter tau, τ), which is even heavier and extremely unstable, with an electric charge of -1. The tau neutrino (symbolized by 'v' with a 'τ' subscript) is its neutral partner, with a charge of 0. These particles are progressively heavier and more unstable than their predecessors.
For each lepton, there is a corresponding anti-lepton. The anti-electron is called a positron (e+), with a charge of +1. The electron anti-neutrino (v with an 'e' subscript and a bar over the 'v') has a charge of 0. Similarly, there are the anti-muon (µ+) and the muon anti-neutrino (v with a 'µ' subscript and a bar), and the anti-tau (τ+) and the tau anti-neutrino (v with a 'τ' subscript and a bar).
It's important to remember the charges of leptons. The charged leptons (electron, muon, tau) interact with the electromagnetic force, while the neutral neutrinos do not. Knowing these charges is crucial for understanding how different forces act on leptons, especially in exam questions that may try to 'trap' students by asking about electromagnetic forces on neutrinos.