define the ff.

a.current

a flow of electricity which results from the ordered directional movement of electrically charged particles.

In electrostatic situations the electric field is zero everywhere within the conductor, and there is no current.

The motion of the electrons is random, so there is no net flow of charge in any direction and hence no current.

conventional current-choice or convention for the direction of current flow definition of current- I=dQ/dt The SI unit of current is the ampere; one ampere is defined to be one coulomb per

second (1 A = 1 C/s). This unit is named in honor of the French scientist André Marie Ampère (1775–1836). direct current- direction of the current is always the same. alternating current- the current continuously changes direction. examples 25.7-25.5-25.1-25.6-

b. voltage

an electromotive force ( EMF) or potential differ ence expressed in volts. Potential is potential energy per unit charge ( V=U/qo or U=qoV where U=potential

energy;qo=unit charge. The SI unit of potential, called one volt (1 V) in honor of the Italian electrical

experimenter Alessandro Volta (1745–1827), equals 1 joule per coulomb: 1 V = 1 volt = 1 J/C = 1 joule/coulomb

potential due to a point charge: V=U/qo=1

4 π € oqr

potential due to a collection of point charge: V= Uqo

= 14 π € o∑i

qiri

potential due to a continuous distribution of charge: V=1

4 π € o∫dqr

1 V/m= 1N/C terminal voltage, source with internal resistance: Vab= Є-Ir, where Є=EMF and Ir=

internal resistance.

c.resistance

the degree to which a material or device opposes the passage of an electric current, causing energy dissipation.

the resistance of a wire or other conductor of uniform cross section is directly proportional to its length and inversely proportional to its cross-sectional area.S

conductors have zero or least amount of resistance insulators have greatest or infinite amount of resistance Semiconductors have resistance transitional between those of conductors and insulators. A circuit device made to have a specific value of resistance between its ends is called

a resistor. The SI unit of resistance is the ohm, equal to one volt per ampere ( 1Ω= 1 V/A).

The kilohm (1kΩ= 10^3 Ω) and megohm (1 MΩ= 10^6 Ω) are commonly used. relationship among voltage, current, and resistance: V=IR The resistance of a cylindrical conductor is related to its resistivity ρ, length L, and cross-

sectional area A: R=ρLA

(give at least 5 ex. with solution use univ. college physics)

define the ff.

a. power the rate of doing work, measured in watts or horse power. the power P equals the product of the potential difference and the current. rate at which energy is delivered to or extracted from a circuit element:

P=VabI

power delivered to a resistor: P=VabI=I^2R=Vab2

Renergy

is the property of the body or system of bodies by virtue of which work can be done. It is also defined as the ability to do work. Energy is a scalar quantity.

A measure of this capacity, expressed as the work that it does in changing to some specified reference state.

It is measured in joules (SI units) Definition of energy: E=Pt

3. ohm’s law the principle that the electric current passing through a conductor is directly proportional

to the potential difference across it, provided that the temperature remains constant. the constant of proportionality is the resistance of the conductor.

It was discovered in 1826 by the German physicist Georg Simon Ohm (1787–1854).

definition of ohm’s law: R=V/I

(give 5 problems applying the ohm’s law)