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# Physics 220 Final

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

Faraday's Law in Words | The emf around a loop equals the rate at which the magnetic flux within the loop is changing. emf=-dBFlx/dt |

3 ways to change flux | -Change B in a loop -Change area of loop -change orientation of loop |

looping electric field lines | Faraday’s Law - The source of looping electric field lines is changing magnetic flux. |

Lenz's Law | The direction of induced current always opposes the change in magnetic flux. |

Commutators and Brushes AC DC | These allow electrical connections to be made by pressing conductors together. -Uses double commutators(sinusoidal wave) -Bouncing wave |

The Split Commutator | changes the end of the loop connected to the positive terminal of the battery every half cycle (DC) |

Generator | Motor operated in reverse |

Inductor | a coil of wire placed in a circuit. usually solenoidal or toroidal windings. - oppose change in circuits. |

An Inductor in a DC Circuit | produces a B field and the wire has a resistance. |

An Inductor in an AC Circuit | Changing current continually, hence, changing B field, self inductions |

LR CIrcuits resistor is large Inductor is large | -takes shorter time for current to decrease, decreases induced current -better at making induced current, takes longer for induced current to decrease |

Kirchoff's Loop Law | The voltage around the loop at any given time must be zero. q(t)=Asin(wt)+Bcos(wt) q(t)=CVocos(wt) at max |

LC Circuits | Initially the capacitor is charged. No current flows as the inductor initially prevents it. Energy is in the electric field of the capacitor |

The Oscilloscope | Measures voltage as a function of time Usually used for waves with repeated waveforms Starts a trace when the wave has a certain value Can compare two voltages Sometimes can show single pulses also |

Inductive Reactance | wL has a role that is similar to resistance – it relates voltage to current. XsubL Large at high f |

Capacitive Reactance | 1/wC - XsubC Large at low f |

Resonance frequency | when inductive reactance = capacitive reactance |

Circuit Rules for AC Circuits - Parallel | 1-their voltage phasors are the same. 2-their current phasors add to give the total current |

Circuit Rules for AC Circuits - Series | 1-their current phasors are the same. 2-their voltage phasors add to give the total voltage. |

Impedance | the combined “effective resistance” of circuit elements. |

effective AC current | Irms |

Displacement current | change in electric flux |

Maxwell’s Term | The displacement current term is called “Maxwell’s Term” in Ampère’s Law The amount of magnetic field lying along a closed (Amperian) loop is proportional to the rate at which electric flux through the loop changes. |

Faraday's Law | The amount of electric field lying along a closed (Amperian) loop is proportional to the rate at which magnetic flux through the loop changes. looping electric |

Ampère’s Law | The amount of magnetic field lying along a closed (Amperian) loop is proportional to the current passing through the loop. looping b |

Gauss's LAw of Magnetism | The net number of magnetic field lines passing through a closed (Gaussian) surface is zero. spreading b |

Gauss's Law of Electricity | The net number of electric field lines passing through a closed (Gaussian) surface is proportional to the charge enclosed. spreading E |

Fields of Accelerating Charges1 | Moving charges produce both electric and magnetic fields Acceleration fields are “doglegs” in field lines produced when charges accelerate. |

Fields of Accelerating Charges2 | Acceleration fields become perpendicular to the direction the filed moves. Acceleration fields fall off as 1/r rather than 1/r 2. |

Characteristics of Radiation | Produced by accelerating charges Perpendicular to the direction the field moves. Fall off as 1/r rather than 1/r 2 Emax=cBmax |

Intensity | power per unit area or energy/area/time. |

Bandrate | about same frequency |

Coercive Force | The external field needed to bring the internal field back to zero |

REsidual magentization | When the external field goes to zero, some domains remain aligned |

EMF | Any voltage, as from a battery effective voltage produced by an induced electric fields accel charges - changing curent in circuit motional emf -charges in a conductor moving in field. |

Equipotential surfaces | Have a constant value of electric potential (voltage) everywhere on the surface Are perpendicular to the field everywhere Are closer together where the field is stronger when we make a set of surfaces separated by equal voltage differences |