Physics Exam 3 Flashcards
(52 cards)
electric current is defined as
current is related to current density by
J= same direction as positive velocity charges
dA= vector perpendicular to area dA
Positive charge carriers acquire a drift speed Vd in the direction of the electric field, equation given by:
ne= charge carrier density.
The Resistance of a conductor is given by
Equations involving resistivity and conductivity
The Resistance R of a conducting wire of length L and uniform cross section is
resistivity variation with temperature
Ohm’s Law
is an assertion that the current through a device is always directly proportional to the potential difference applied to the device.
Equation for drift speed
the rate of electrical energy transfer
emf in terms of work
the emf of an emf device is the work per unit charge that the device does in moving charge from its low-potential terminal to its high-potential terminal. The SI unit for emf is the joule per coulomb
What determines the direction of the current in a battery?
The actual direction of the current in the circuit is determined by the battery with the larger emf
What is the loop rule
The algebraic sum of the changes in potential encountered in a complete traversal of any loop of a circuit must be zero.
What is the resistance rule?
For a move through a resistance in the direction of the current, the change in potential is -iR; in the opposite direction it is +iR.
What is the EMF rule?
What is the rule for resistors in series?
When a potential difference V is applied across resistances connected in series, the resistances have identical currents i. The sum of the potential differences across the resistances is equal to the applied potential difference V. (ser-i)
potential difference
Current in a circuit
To find the potential between any two points in a circuit
start at one point and traverse the circuit to the other point, following any path, and add algebraically the changes in potential you encounter.
Potential Difference across a real battery
Electric Field is in the direction
of plus to minus
Power of an EMF device
sign of potential when crossing a current
sign of potential when crossing a battery
When you cross a resistor in the same direction as the current, that’s also a drop in potential so it’s a negative change in potential. Crossing a resistor in the opposite direction as the current gives you a positive change in potential.
When you cross a battery from the - side to the + side, that’s a positive change. Going the other way gives you a drop in potential, so that’s a negative change.
