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# EK Physics 7

### electricity and magnetism

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

units of charge | coulombs (C) |

universal law of conservation of charge | the universe has no net charge, net charge is created by separating electrons from protons |

Coulomb's law | F = k*q1*q2/r^2 formula describing magnitude of the force of repulsion or attraction btw two charged objects |

electric field lines always go... | from positive to negative |

the closer electric field lines are... | the stronger the electric field |

units to describe electric field | N/C or V/m |

electric field created by point charge formula | E = k*q1/r^2 |

Force on charge q in an electric field | F = Eq |

potential energy of charge in an electric field | U = Eqd |

electric potential energy from coulomb's law | U = k*q1*q2/r |

what is the electric potential for particles separated by an infinite distance? | zero |

voltage | potential for work by an electric field in moving any charge from 1 pt to another = Ed |

units for voltage | volts = J/C |

voltage due to a point charge | V = k*q1/r |

what is a good conductor? | allows e's to flow relatively freely, ex: metals |

what is a poor conductor/good resistor? | hold e's tightly in place, ex: network solids like diamond and glass |

induction | process to charge a conductor |

current | moving charge, given in amps (A = C/s), its flow is in the direction of positive charge |

circuit | cyclical pathway for moving charge |

resistivity | quantitative measure of how much substance resists flow of charge |

resistance | (R) is the quantitative measure of an object of articular shape and size to resist flow, measured in ohms; depends on resistivity, length of wire and cross sectional area of wire |

voltage relates to current and resistance by | V = iR (ohm's law) |

the amount of current flowing into any node must be ____ | the same that flows out. |

the voltage around any path in a circuit must sum to ____ | zero |

electromotive force | EMF, rates the batteries, analogous to voltage |

capacitor | used to temporarily store energy in a circuit |

parallel plate capacitor | two plates made from conductive material separated by small distance where 1 plate holds positive charge and the other holds exact same amt of neg charge |

electric field in capacitor | E = (1/K)*(Q/A*eo) where K is dielectric constant, Q is charge on either plate, A is the area of the plate, and eo is derived from Coulomb's constant |

capacitance | ability to store charge per unit voltage C = Q/V |

capacitance of parallel plate capacitor | C= K(A*eo/d) where d is sep distance and A is the plate area *increased surface area increases C and increasing sep distance decreases C |

energy stored in capacitor = | U = 1/2*QV = 1/2*CV^2 = 1/2*QC^2 |

dielectric constant | substance btw plates of capacitor, insulator material, acts to resist creation of electric field so ti can store more charge |

resistors in series | Reff = R1 + R2 + R3 +... |

resistors in parallel | 1/Reff = 1/R1 + 1/R2 + 1/R3 .. |

capacitors in series | 1/Ceff = 1/C1 + 1/C2 + 1/C3 ... |

capacitors in parallel | Ceff = C1 + C2 + C3 ... |

electrical power | P = iV = i^2*R = V^2/R |

DC current | direct current, where net movement of e's is in 1 direction around circuit |

AC current | alternating current, created by oscillating e's back and forth in SHM |

Vmax in AC current | =sqrt(2)*Vrms |

imax in AC current | =sqrt(2)*irms |

magnetic field unit | tesla, T |

magnetic field lines go from.. | north to south poles |

magnetic field created by... | CHANGING electric field |

right hand rule for magnetic field - the palm is... | force of charge moving thru magnetic field |

right hand rule for magnetic field - the thumb is... | velocity of charge moving thru magnetic field |

right hand rule for magnetic field - the fingers are... | direction of magnetic field |

force of a charge moving thru magnetic field = | F = qvBsin(theta) where theta is the angle btw magnetic field and velocity of charge |

force is directed _____ to both the velocity and magnetic field | perpendicularly |

does magnetic force do work? | no, the force is always perpendicular to velocity and magnetic field so cannot apply force in the direction of movement |

force on a current carrying wire in a magnetic field = | F = iLBsin(theta) where L is the length of the wire, and theta is the angle between wire and B |

a changing magnetic field ___ | creates an electric field, but this field is NON CONSERVATIVE--> loop of wire pulled out of magnetic field will develop current in wire |

faraday's law | describes how changing magnetic field induces emf = flux (magnetic field of over an area over time) |

Lenz' law | induced current will create a magnetic field opposing the inducing magnetic field |

eddy currents | result when a conductor is moved thru magnetic field - pendulum in a magnetic field will stop swinging from the resistivity and absorption of internal energy so KE changed to heat |

Created by:
miniangel918