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# phyx eqns E & M

Question | Answer |
---|---|

Electric Field (two) | E = F / q or E = k Q / r^2 q= point charge |

Electric Potential Energy | U = q V or W = q V V= Electric Potential |

Average Electric Field | E = -V/r |

Capacitance | C = Q/V Q= Charge |

Capacitance with Area | C = εo A/ r εo = vacuum permittivity constant |

Electric Potential | V = k Q / r |

Electric Charge | Q= CV |

Energy Stored in a Capacitor (two) | U = 1/2 QV or U = 1/2 CV^2 |

Resistance | R = pl/ A p= resistivity l= length A= Area |

Ohm's Law | V= IR |

Electric Power | P = IV |

Total Capacitance in Parallel | Ct = C1 + C2 + C3 |

Total Capacitance in Series | 1/Ct = 1/C1 + 1/C2 + 1/C3 |

Total Resistance in Series | Rt = R1 + R2 + R3 |

Total Resistance in Parallel | 1/ Rt = 1/R1 + 1/R2 + 1/R3 |

Force from a Magnetic Field on a moving charge | FB = q v B sin θ When the angle is 90 the F is at its max. When it is parallel there is not force |

Force from a Magnetic Field from a current in a wire | FB = B I l sin θ |

Magnetic Field from a current in a wire or Ampere's Law | B = μo I / 2πr |

Magnetic Flux | φ = BA cos θ |

Average Induced EMF | € = - N Δφ / Δt N = Number of Loops |

Induced EMF in a moving conductor | € = B l v |

Right Hand Rule for Force | Fingers- B Thumb- v Palm - F |

Right Hand Rule for Current | Place thumb in direction of the current. Curve fingers point in the direction of the magnetic field. |

Force of a charge moving in a curved path (three) | F = mac = qvB = mv^2/r |

Kirchoff's Junction Rule | The sum of all currents entering a junction is the equal to the sum of all currents leaving that junction. |

Kirchoff's Loop Rule | The sum of the voltage changes around any closed pat of the circuit must be zero. |

Magnetic Field inside a Solenoid | B = μo n I μo = Vacuum Permeability Only if air is in the solenoid, if there is something else use μ which is magnetic permeability n= number of loops per unit length I = Current |