Electrostatics March 17 and 18, 2014

Warm-Up Which graph best represents the relationship between electrostatic force F and distance d between two charges?

Objectives 5A Research and describe the concepts of electromagnetic forces. 5E Characterize materials as conductors or insulators based on their electrical properties. 5C describe and calculate how the magnitude of the electrical force between two objects depends of their charges and the distance between them.

Electric Charge ParticleCharge (C)Mass (kg) electron-1.60 x proton neutron

Electric Charge ParticleCharge (C)Mass (kg) electron-1.60 x proton+1.60 x neutron

Electric Charge ParticleCharge (C)Mass (kg) electron-1.60 x proton+1.60 x neutron0

Electric Charge ParticleCharge (C)Mass (kg) electron-1.60 x x proton+1.60 x x neutron x

Coulomb or C C: Coulomb  Unit of Charge μC: micro Coulomb C nC: nano Coulomb C pC: pico Coulomb C

Let’s Practice. Convert 6.0 nC to C. 1nC= C 6.0 nC= 6.0 x C

Let’s Practice. Convert 12.5 pC to C. 1pC= C 12.5 pC= 12.5 x C = 1.25 x C

Let’s Practice. How many electrons does a 6.0 nC charge represent? (note that an electron has the charge of 1.6 x C ) Total charge = charge of an electron x number of electrons 6.0 x C = 1.6 x C x number of electrons 6.0 x C / 1.6 x C = number of electrons 3.8 x = number of electrons

Charging by contact The net charge of a balloon after being rubbed against a wool sweater is ( ). The net charge of a sweater after being rubbed by a balloon is (positive). negative

Balloons and Static Electricity The sweater ( ) electrons, and the balloon ( ) electrons. gained lost

Polarization: Shift of charge of an insulator in the presence of a charged object

Affinity for Electrons Materials have different affinity for electrons. Fur and a rubber rod rubbed together  Fur lost electrons A glass rod and silk rubbed together  Glass lost electrons

John Travoltage When John moved his foot on the carpet, what happened? Electrons moved from the carpet to John and gathered in his body. When John turn his finger on the door, what happened to the built-up electrons in his body? Electrons moved from his body to the door handle.

Grounding The process of touching the door knob to drain the charge is called ( ). Describe two situations where you collected and then discharged static electricity through grounding. When you touch other people When you touch a car grounding

Charging by induction The process of charging a conducting object without contact

Induction

Coulomb’s Law q1q1 q2q2 d q 1 : +, q 2 : +  force of repulsion q 1 : -, q 2 : +  force of attraction

Coulomb’s Law Coulomb constant k = 9.0 x 10 9 Nm 2 /C 2

Gravitational force vs. electrical force Compare two formulas. electrical force

Let’s practice. Two identical charges of 5.2 pC are separated by a distance of 1m. What is the force between them? F= 9.0 x 10 9 x 5.2 x x 5.2 x / (1 x 1) F=2.4 x N

Force and charge Electric force varies as the product of charges. If one charge doubles, then the force ( ). If both charge doubles, then the force ( ). If both charge are halved, then the force decreases to ( ). If one charge is halved, then the force decreases to ( ).

Force and distance Electric force inversely varies as the square of distance. If the distance doubles, then the force decreases to ( ). If the distance triples, then the force decreases to ( ) as great. If the distance is halved, then the force increases to ( ) as great.

Force, distance, and charge If the charge on each particle and the distance between the two particles doubles, then the force ( ). If the charge on each particle triples and the distance between the two particles doubles, then the force ( ).