1 Physics Chapter 32 Electrostatics Personal Ads : e - rich…seeks e - poor for bonding, conducting, and long term relationship. Resistance a plus.

Electrical Forces and Charges The fundamental rule at the base of all electrical phenomena is that like charges repel and opposite charges attract. ources/bu_semester2/index.htmlhttp://webphysics.davidson.edu/physlet_res ources/bu_semester2/index.html s/nforcefield.htmlhttp:// s/nforcefield.html Electrostatics is electricity at rest.

Electrical Forces and Charges Electrical forces arise from particles in atoms. In the simple model of the atom, protons in the nucleus attract the electrons and hold them in orbit. Electrons are attracted to protons, but electrons repel other electrons. The fundamental electrical property to which the mutual attractions or repulsions between electrons or protons is attributed is called charge. By convention, electrons are negatively charged and protons positively charged. Neutrons have no charge and are neither attracted nor repelled by charged particles.

Conservation of Charge Conservation of Charge An object that has unequal numbers of electrons and protons is electrically charged. An atom with a net positive charge is a positive ion; it has lost one or more electrons. An atom with a net negative charge is a negative ion; it has gained one or more electrons. The principle that electrons are neither created nor destroyed but are simply transferred from one material to another is known as conservation of charge. Law of Conservation of Electric Charge- During any process, the net electric charge of an isolated system remains constant ( is conserved). Total charge before= Total charge after.

Coulomb’s Law q = charge of particle; +q or -q Coulomb’s law states that for charged particles or objects that are small compared with the distance between them, the force between the charges varies directly as the product of the charges and inversely as the square of the distance between them. Electric filed lines applet

Coulomb’s Law F = kq 1 q 2 /d 2, where d is the distance between the charged particles q 1 represents the quantity of charge of one particle and q 2 the quantity of charge of the other particle. The SI unit of charge is the coulomb, abbreviated C. The proportionality constant k in Coulomb’s law is 9.0 x 10 9 Nm 2 /C 2. 1 electron has a charge of 1.60 x C {either (+) or (-)}. Like all other forces, the electrostatic force between two charged objects is measured in Newtons (N). -F = attraction and +F = repulsion

Coulomb’s Law 1.Consider a pair of charged particles separated by a distance d. If the distance between the particles is multiplied by 4, how will the electrostatic force between the particles change? 2.If the charge of each particle tripled and the distance also tripled, how would the electrostatic force between the particles change? 3.If the charge of one particle doubled and the charge of the other particle tripled, how would the electrostatic force between the particles change? 4.If the charge of one particle were reduced to one-half the original charge and the distance between the charges were multiplied by 2, how would the electrostatic force between the particles change?

Coulomb’s Law Calculating Coulomb Forces Applet 1.Sue rubs two latex balloons against her hair, causing the balloons to become charged negatively with 2.0 x C. She holds them a distance of 0.70 m apart. a) What is the electric force between the two balloons? b) Is it one of attraction or repulsion? 2.Two pieces of puffed rice become equally charged as they are poured out of the box and into Kirk’s cereal bowl. If the force between the puffed rice pieces is 4 x N when the pieces are 0.03 m apart, what is the charge on each of the pieces?

9 How does the electrical force between the proton and the electron in the hydrogen atom compare to the gravitational force between these two particles? Given: Bohr radius, r = 5.29 x m, use the mass of the proton and electron to two decimal places.