electrostatics march 17 and 18, 2014. warm-up which graph best represents the relationship between...
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Electrostatics
March 17 and 18, 2014
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
Particle Charge (C) Mass (kg)electron -1.60 x 10-19
protonneutron
Electric Charge
Particle Charge (C) Mass (kg)electron -1.60 x 10-19
proton +1.60 x 10-19
neutron
Electric Charge
Particle Charge (C) Mass (kg)electron -1.60 x 10-19
proton +1.60 x 10-19
neutron 0
Coulomb or C
• C: Coulomb Unit of Charge• μC: micro Coulomb 10-6 C• nC: nano Coulomb 10-9 C• pC: pico Coulomb 10-12 C
Let’s Practice.
• Convert 6.0 nC to C.• 1nC= 10-9 C• 6.0 nC= 6.0 x 10-9 C
Let’s Practice.
• Convert 12.5 pC to C.• 1pC= 10-12 C• 12.5 pC= 12.5 x 10-12 C = 1.25 x 10-11 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 10-19 C )
• Total charge = charge of an electron x number of electrons
• 6.0 x 10-9 C = 1.6 x 10-19 C x number of electrons• 6.0 x 10-9 C / 1.6 x 10-19 C = number of electrons• 3.8 x 1010 = 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
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
q1 q2d
q1: +, q2: + force of repulsion
q1: -, q2: + force of attraction
Coulomb’s Law
Coulomb constant k = 9.0 x 109 N•m2/C2
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 109 x 5.2 x 10-12 x 5.2 x 10-12 / (1 x 1)• F=2.4 x 10-13 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 ( ).