Electric Force

Electric Force

Middle School

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Learning Objectives

• Explain how electric fields create forces between charged objects without them touching.

• Model how potential energy changes when the position of charged objects is changed.

• Define electric current and its connection to voltage and resistance.

• Compare different ways of static charging and the process of static discharge.

Key Vocabulary

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Electric Charge

A fundamental property of matter that can be either positive, negative, or completely neutral.

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Electric Force

The invisible force of attraction or repulsion that exists between any two charged objects.

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Electric Field

A region of space around a charged object where its electric force is exerted.

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Potential Energy

The stored energy a system of charges holds due to their positions or arrangement.

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Electric Current

The continuous flow of electric charge through a material, which is measured in amperes (A).

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Circuit

A complete, closed path around which an electrical current can flow continuously without interruption.

Key Vocabulary

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Voltage

Voltage is the potential energy difference per unit of charge that is responsible for pushing electric current.

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Static Electricity

This term describes a buildup of stationary electric charge on the surface of an object or material.

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Conductor

A conductor is a type of material that allows electric current to flow through it very easily.

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Insulator

An insulator is a specific type of material that resists the flow of electric current through it.

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Magnetic Force

This is a fundamental force that arises from moving electric charges acting upon other moving electric charges.

Electric Charge and Force

• Electric charge can be positive, negative, or neutral.

• Opposite charges attract, while like charges repel each other.

• Force increases with more charge and decreases with more distance.

Multiple Choice

Which statement correctly describes the fundamental rule of interaction between electric charges?

• Charges that are alike attract each other.

• Charges that are opposite repel each other.

• Like charges repel, and opposite charges attract.

• Neutral objects are repelled by all charges.

Multiple Choice

If two objects with negative charges are moved farther apart, how does the electric force between them change?

• The repulsive force will become stronger.

• The repulsive force will become weaker.

• The force will change from repulsive to attractive.

• The force will not change in strength.

Multiple Choice

Imagine two objects with positive charges are repelling each other. According to the principles of electric force, what change would cause the repulsive force between them to become stronger?

• Increase the distance between the objects.

• Decrease the amount of charge on the objects.

• Increase the amount of charge on the objects.

• Change one of the charges from positive to neutral.

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Electric Fields

Positive Charge

• An electric field is an invisible region of influence that surrounds a charged object.

• Field lines for a positive charge point outward, showing the repulsion of other positive charges.

• The closer the field lines are to each other, the stronger the electric field is.

Negative Charge

• This field allows forces to act on objects from a distance without physical contact.

• Field lines for a negative charge point inward, showing the attraction of positive charges.

• The direction of these lines helps predict how charged objects will interact with one another.

Multiple Choice

What is the definition of an electric field?

• An invisible region of influence that surrounds a charged object.

• A force that requires direct physical contact between objects.

• The specific path an electron follows in a wire.

• A type of energy stored within a battery.

Multiple Choice

What does the direction of electric field lines represent?

• The temperature of the object creating the field.

• The direction of the force the field would exert on a positive charge.

• The exact mass of the object creating the field.

• The speed at which the electric field is moving.

Multiple Choice

If you compare two diagrams of electric fields, what can you conclude about the area where the field lines are closest together?

• The electric field is stronger where the lines are closer together.

• The electric field is weaker where the lines are closer together.

• The charge must be negative if the lines are close together.

• The charge is moving at a high speed.

Modeling Potential Energy

• Electric potential energy changes with the distance between charged objects.

• Pushing repelling positive charges together increases the system's potential energy.

• Allowing attracting opposite charges to move closer decreases potential energy.

Multiple Choice

Which factor is most important in determining the electric potential energy between two charged objects?

• The distance between the objects

• The temperature of the objects

• The mass of the objects

• The color of the objects

Multiple Choice

What is the effect on a system's potential energy when two repelling positive charges are pushed closer to each other?

• The potential energy increases

• The potential energy decreases

• The potential energy is unchanged

• The charges lose their energy

Multiple Choice

A system contains a positive charge and a negative charge that are attracting each other. What would happen to the system's potential energy if the charges were allowed to move closer?

• The potential energy would decrease

• The potential energy would increase

• The potential energy would stay the same

• The charges would begin to repel

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Electric vs. Magnetic Forces

Electric Force

• Acts on charged particles, whether they are stationary or in motion.

• This force can be either attractive, pulling charges together, or repulsive, pushing them apart.

• A stationary charged object like a pith ball will be deflected by an electric field.

Magnetic Force

• Acts on moving charged particles and on the poles of magnets.

• A stationary charge does not create or feel a magnetic force at all.

• A stationary charged object is completely unaffected by a nearby magnetic field.

Multiple Choice

Under which condition does a magnetic force act on a charged particle?

• Only when the particle is moving

• Only when the particle is stationary

• Whether the particle is moving or stationary

• Only when the particle is losing its charge

Multiple Choice

What is a key difference in how electric and magnetic forces affect a stationary charged object?

• An electric force will affect the object, but a magnetic force will not.

• A magnetic force will affect the object, but an electric force will not.

• Both forces will cause the object to move in a circle.

• Neither force will have any effect on the object.

Multiple Choice

A charged pith ball is placed inside a field and is immediately deflected. Based on this observation, what can be concluded about the field?

• The field is electric, because it exerted a force on a stationary charged object.

• The field is magnetic, because it caused the pith ball to be deflected.

• The field could be either electric or magnetic.

• The field must be a combination of electric and magnetic forces.

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What is Static Electricity and Discharge?

• Static electricity is the buildup of a stationary electric charge on an object.

• ​Charging can happen through friction (rubbing) or conduction (direct physical contact).

• Induction rearranges charges in an object without any direct physical contact.

• Static discharge is the loss of charge, which can create sparks or lightning.

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Multiple Choice

What is static electricity?

• The buildup of a stationary electric charge on an object.

• The loss of an electric charge from an object.

• The flow of electric charge through a wire.

• The rearrangement of charges using a magnet.

Multiple Choice

What is the primary difference between how objects are charged by induction versus by friction or conduction?

• Friction and conduction require direct physical contact, while induction does not.

• Induction is the only method that can create a spark.

• Friction involves rubbing, while conduction and induction are the same.

• Only induction can be used to charge a metal object.

Multiple Choice

After rubbing a balloon on their hair, a student has a buildup of stationary charge. What is the most likely outcome when the student brings the balloon close to a metal doorknob?

• A static discharge will occur from the student's hand to the doorknob.

• The doorknob will become charged by induction before the student touches it.

• The electric charge will stay on the student's body.

• The doorknob will transfer a charge to the student through friction.

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Common Misconceptions

Misconception	Correction
Forces can only happen when objects touch.	Electric and magnetic forces act at a distance through fields.
Batteries create new charges.	Batteries are an energy source, pushing existing charges.
Electric current is the flow of electrons.	Current is the direction positive charges would flow.

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Summary

• Electric charges create electric forces and are surrounded by electric fields.

• Moving charges against their natural force increases the system's potential energy.

• Electric forces act on both stationary and moving charges.

• Static electricity is stationary charge, while current is flowing charge driven by voltage.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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