4A1 Electrostatics Flashcards
Explore electric and induced charge, including their role in electric forces, fields, and potential.
Define:
Electric charge
Fundamental property of matter that determines how particles interact through electromagnetic forces.
Charged objects experience attraction or repulsion depending on their charge type and the presence of an electric field. The SI unit of electric charge is the coulomb (C).
What are the two types of electric charge?
- Positive
- Negative
Protons are positively charged, while electrons are negatively charged.
What is the charge of a single proton?
+1.6×10^(−19) C
This is known as the elementary charge (𝑒), the smallest unit of electric charge. An electron carries the same magnitude of charge but with a negative sign.
Define:
Coulomb
Unit of electric charge in the SI system.
It is equal to the charge of approximately 6.24 × 10¹⁸ electrons. One Coulomb is defined as the charge transferred by a current of one ampere in one second.
True or False:
Like charges repel, and opposite charges attract.
True
This principle is a fundamental law of electrostatics, as described by Coulomb’s Law.
What does it mean that charge is quantized?
Electric charge always exists as an integer multiple of the elementary charge, ±1.602 × 10⁻¹⁹ C.
This fundamental property was demonstrated by Millikan’s oil-drop experiment.
Fill in the blank:
A neutral object has ______ amounts of positive and negative charges.
equal
Neutrality is achieved when charges cancel out.
Define:
Ion
Atom or molecule that has gained or lost one or more electrons, acquiring a net positive or negative charge.
Positive ions are called cations, while negative ions are called anions.
How do electric charges behave during a thunderstorm?
Charges build up inside clouds, leading to lightning bolts when the forces become large enough.
Lightning carries a lot of charge and energy.
What happens during electrical induction?
Charged object causes a redistribution of charges in a nearby neutral object without direct contact.
This is the principle behind charging by induction.
Fill in the blank:
The total electric charge in an isolated system is _______.
conserved
This is the principle of charge conservation. Charges are merely transferred, not created.
True or false:
Only conductors can experience induced charges.
False
Both conductors and insulators can experience induced charges, but the process differs.
Why does a charged balloon stick to an insulating wall?
The wall’s molecules become polarized, and the positive charges within the molecules shift slightly toward the negative charged balloon.
## Footnote
This creates a localized attractive force, allowing the balloon to stick even though the wall is neutral. The charges in the insulating wall do not move freely but shift slightly within each molecule, causing the balloon to stick.
Fill in the blank:
When a negatively charged rod is brought near a metal sphere, the _____ ______ in the sphere are repelled, leaving one side positively charged.
free electrons
Conductors allow free electrons to move, causing a redistribution of charge when near a charged object.
How do conductors and insulators differ in electron movement and charge behavior?
- Conductors allow free movement of electrons, enabling charge flow.
- Insulators restrict electron movement, keeping charges localized.
- Conductors have free-moving electrons, allowing electric charge to flow easily, making them ideal for wires and electrical circuits.
- Insulators restrict electron movement, keeping charges localized and preventing charge flow, which makes them useful as electrical insulators.
True or false:
The net charge of a system changes during induction.
False
Induction redistributes existing charges without altering the net charge.
What happens to the total charge in a system when two objects are rubbed together?
It remains constant, but electrons are transferred from one object to the other, making one positively charged and the other negatively charged.
This process is called triboelectric charging.
Fill in the blank:
When a negatively charged rod touches a neutral sphere, the sphere becomes _______ ______.
negatively charged
Electrons are transferred from the rod to the sphere.
Explain the principle behind grounding an object.
Grounding provides a path for excess charge to flow to the Earth, neutralizing the object without violating charge conservation.
The Earth acts as an infinite reservoir of charge.
Define:
Charge transfer
The process by which electric charge moves from one object to another.
Charge transfer can occur through various mechanisms.
Explain the principle of charging by conduction.
It occurs when a charged object physically touches another object, transferring charge between them.
The charge transferred depends on the materials’ properties.
What happens when you touch a metal doorknob after walking on a carpet?
You may feel a small electric shock because excess electrons that built up on your body while walking on the carpet suddenly transfer to the metal doorknob upon contact.
This is an example of charging by conduction, where direct contact enables the transfer of charge.
Fill in the blanks:
Induction occurs when a charged object is brought near a neutral object, causing a redistribution of charges without _______ _______.
direct contact
Induction is a method of charging that relies on the influence of the electric field of a charged object.
Define:
Electrostatic discharge
Rapid transfer of the electrical charge between two objects, equalizing the charge.
It often produces light, sound, or heat. It often occurs when charge build-up reaches a critical point.
What causes a static electricity discharge?
When a charged object comes into contact with a conductor or another object at a different electric potential, allowing excess charge to transfer suddenly.
This often results in a small shock, especially in dry environments.
What does Coulomb’s law state?
The force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
The equation is F = k * (q1 * q2) / r^2
True or false:
Coulomb’s law applies only to charged particles in a vacuum.
False
It can also be applied in media, but the permittivity of the medium must be considered.
What conditions must be met to apply Coulomb’s law?
Charges must be:
- Stationary
- Point particles
- Non-overlapping
These conditions ensure that Coulomb’s law can be accurately applied without the complexities introduced by motion or extended objects.
Explain the role of distance in Coulomb’s law.
The force between two charges decreases with the square of the distance between them.
This is an example of an inverse square law, where doubling the distance reduces the force to one-fourth its original value.
What is the significance of the superposition principle in Coulomb’s law?
It allows the calculation of the net force on a charge due to multiple other charges by summing the individual forces.
This principle is essential for analyzing systems with more than two charges.
How does Coulomb’s law compare to Newton’s law of gravity?
Both are inverse-square laws and involve a product of a specific property (charge for Coulomb’s law and mass for gravity).
Unlike gravitational force, electrostatic force can be either attractive or repulsive.
Why does the gravitational force dominate over the electric force between the Earth and the Moon?
Because the Earth and Moon are electrically neutral on a large scale, gravitational forces predominate due to their massive sizes.
Gravitational forces are always attractive, while electric forces can cancel out when charges are balanced.
What is the range of Coulomb force?
Coulomb’s law is valid for any distance, and the force decreases with the square of the distance between the charges.
The force tends to zero as the distance approaches infinity.
True or false:
The force between charges is always attractive.
False
Like charges repel, and opposite charges attract, as described by Coulomb’s law.
Fill in the blank:
If the distance between two charges is halved, the force between them ________.
quadruples
This follows the inverse square relationship in Coulomb’s law.
Define:
Electric field
Region around a charged object where other charges experience a force.
Its unit is newtons per coulomb (N/C).
True or false:
The direction of the electric field is always from a positive charge to a negative charge.
True
This is a convention used to represent the direction of force on a positive test charge.
True or false:
Electric field lines can cross each other.
False
Electric field lines cannot cross because that would imply two different directions for the field at the same point, which is impossible.
How do electric field lines indicate the strength of an electric field?
The density of field lines represents field strength: closer lines indicate a stronger field, while sparse lines indicate a weaker field.
Field line density is proportional to field magnitude.
Fill in the blank:
The force on a charge in an electric field is given by the equation _______.
F=qE
F is the force, q is the charge, and E is the electric field. This shows the interaction of a charge with an electric field.
Fill in the blank:
The electric field inside a conductor in electrostatic equilibrium is ______.
zero
Charges within a conductor rearrange themselves to cancel any internal field.
What happens when a positive test charge is placed in an electric field?
It follows the electric field lines.
The field lines indicate the direction of the force the charge is experiencing.
Define:
Electric potential
Amount of work needed to move a unit positive charge from a reference point to a specific point in an electric field without acceleration.
Its unit is the volt (V).
What does one volt represent in terms of energy and charge?
1 Joule per Coulomb.
This means that for every Coulomb of charge, 1 Joule of energy is released.
True or false:
Electric potential is a vector quantity.
False
Electric potential is a scalar quantity, unlike electric field or electric force.
Fill in the blank:
The electric potential near a positive charge is ______ compared to farther away.
higher
Electric potential decreases as the distance from a positive charge increases.
True or false:
A positive charge moves naturally to regions of higher electric potential.
False
Positive charges move to regions of lower potential, while negative charges move to regions of higher potential.
Fill in the blank:
Equipotential lines are always _______ to electric field lines.
perpendicular
This ensures that no work is done moving a charge along an equipotential line.
What is the difference between electric potential and potential difference?
- Electric potential is the electric potential energy per unit charge at a specific point in an electric field.
- Potential difference, also called voltage, is the change in electric potential between two points, which drives charge flow in circuits.
Potential difference drives the flow of charges in electric circuits.
Why is potential difference important in everyday life?
Potential difference powers household devices by allowing electric current to flow through circuits.
This concept powers lights, appliances, and charging electronic devices. Electric utilities deliver energy by maintaining a voltage difference between supply and ground points.
Fill in the blank:
Another term for potential difference is ______.
Voltage
Voltage is commonly used to describe the potential difference in electrical circuits.
How are electric potential and the electric field related?
The electric field is the rate of change of electric potential per unit distance; it points in the direction where potential decreases most rapidly.
A strong electric field indicates a steep change in electric potential over a short distance.
Describe the relationship between electric potential and electric potential energy.
- Electric potential energy is the total energy a charge has due to its position in an electric field.
- Electric potential is this energy per unit charge.
U=qV, where U is potential energy, q is charge, and V is electric potential.
What is the formula for electric potential energy?
UE = (k * q1 * q2) / r
Where UE is electric potential energy, k is Coulomb’s constant, q1 and q2 are the charges of the particles, and r is the distance between them.
What is the SI unit of electric potential energy?
Joules (J)
Electric potential energy is expressed in kg m²/s².
What is meant by zero potential in the context of electric potential energy?
It is an arbitrary baseline where electric potential energy is considered to be zero.
Typically, this is measured at a radius of infinity.
What happens to electric potential energy when two opposite charges are separated?
Positive work must be done to separate them.
This is due to the attraction between a positive and a negative charge.
What is the relationship between the charges of two particles and their electric potential energy?
Charges are proportionally related to electric potential energy.
The greater the charges, the greater the potential energy.
