5.2 Electric Current And Resistance Flashcards
What is electric current?
charge that moves past a cross section of a conductor per time I = Q/t the unit is the ampere.
What is potential difference?
The work does per unit charge in moving charge between the two points V= W/q the unit is the volt.
What is the electron volt?
1eV is the energy required to move a charge of e through a potential difference of 1V.
What is electrical resistance?
The ratio of potential difference across a conductor to the current through it R = V/I the unit is the ohm.
What is power?
The rate at which energy is dissipated or produced.
What is ohms law?
At constant temperature many metallic conductors have the property that the current through them is proportional to the potential difference across them. It implies that the resistance is constant. A graph of current through the conductor versus the voltage across it then goes straight line through the origin.
What is a conductor?
A material with lots of free electrons dispersed throughout the metal volume which do not belong to any particular atom. When an electric field is applied within a conductor its free electrons acquire a small drift velocity opposite to the electric field. This means that the electrons have a net motion opposite to the electric field so electric charge is transferred in a direction opposite to the electric field - called electric current.
What is an insulator?
Materials with very few or no free electrons.
What are the formulas for power?
Since current is defined as I=Q/t an amount of charge Q=It gets transferred through a conductor, if the potential difference across the conductor is V the work required to move the electric charge is W=Qv=(It)V. The power which is work per unit time is P=ItV/t thus
P=VI.
Using the definition of resistance R=V/I we have the equivalent from P=VI=RI^2=V^2/R
What is the formula for a resistance of a wire?
For a conductor of uniform cross sectional area R=pL/A where L is the length, A is the cross sectional area of the conductor and the constant p is called the resistivity and depends on the temperature and conductor material.
What is the formula for current?
I=Q/t
I = qnvA where A is the cross sectional area, n is the number of free electrons per unit volume, v is the drift velocity of the electrons and q is the charge on one electron.
