Lesson 20.2- Electric Force( students)
Chapter 20: Static Electricity - Section 2: Electrostatic Force
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Learning Intentions
Understanding the electrostatic force and its properties.
Success Criteria of the Lesson
Define electrostatic force.
Demonstrate electric force.
Explain the use of an electroscope for charging by induction and conduction.
State Coulomb's Law.
Solve questions related to 2D Coulomb's Law.
Examine factors affecting electrostatic force.
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Recall of Lesson 20.1
Two types of charges: Positive & Negative.
Charges can either Repel or Attract depending on their nature.
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Electrostatic Force
Electrostatic force is responsible for the movement of charges, either repelling or attracting them.
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Demonstrating a Force
Electrostatic force acts at a distance and does not require contact between objects.
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Determining Charge with an Electroscope
An electroscope consists of a metal knob and two thin metal foil leaves.
It is used to determine electric charge by observing the behavior of the leaves.
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Charging by Conduction
Contact Method: Bringing a charged rod into contact with the electroscope's knob.
Negative Rod: Electrons transfer to the leaves, causing them to repel.
Positive Rod: Electrons from the leaves transfer to the rod, resulting in positively charged leaves.
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Determining Charge with an Electroscope
To determine the charge of an electroscope, bring a known charge rod near the knob and observe the leaves' behavior.
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Charging by Induction
Charging a neutral object by bringing a charged object close without touching.
Charges in the conductor redistribute without transfer.
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Grounding
Grounding connects a body to Earth to eliminate excess charge.
Earth can absorb large amounts of charge without becoming charged itself.
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Coulomb's Law
Describes the electrostatic force between two charges.
Formula: ( F = k \frac{Q_A Q_B}{r^2} )
( F ): Electrostatic force (N)
( Q_A, Q_B ): Charges (C)
( r ): Separation distance (m)
( k ): Coulomb's constant (( 8.99 \times 10^9 , N \cdot m^2/C^2 ))
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Coulomb's Law Variables
Directly Proportional: Force and charge.
Inversely Proportional: Force and the square of the distance.
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Problem-Solving Strategies for Electrostatic Force
Sketch the system.
Diagram the vectors.
Use Coulomb's law for magnitude.
Determine direction using diagrams.
Perform algebraic operations.
Check the magnitude of the net force.
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Applications of Electrostatic Forces
Electrostatic Painting: Charged droplets for uniform painting.
Electrostatic Precipitators: Collect emissions to reduce pollution.
Photocopy Machines: Use static electricity for toner placement.
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Avoiding Static Charge Buildup
Technicians wear wrist straps to ground themselves.
Lightning rods are grounded to protect buildings.
Page 51
Section 2 Review
Electrostatic Force Relationship: Magnitude is proportional to charge and inversely proportional to distance.
Charging by Induction: What happens when the charging rod is moved away before grounding?
Attraction of Neutral Objects: How charged objects can attract neutral objects.
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Section Self-Check
How to charge an electroscope positively or negatively.
Compare forces between two