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Questions and Answers
What is the unit of electric charge?
Coulomb (C)
What is the interaction between like charges and unlike charges?
Like charges repel each other, unlike charges attract each other.
What happens to polythene when it is rubbed against cloth?
It becomes negatively charged.
What is the location of protons and neutrons in an atom?
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What is the term used to describe the amount of electric charge an object has?
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What is the primary characteristic of a conductor in terms of electric charge?
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Where do static charges reside on a conductor?
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Where does charge tend to accumulate the most on a charged conductor?
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What happens to the ions near a charged object during point discharge?
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What is a demonstration of the effect of point discharge on a charged object?
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What are some functions of a gold leaf electroscope?
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What is the relationship between the force of attraction or repulsion and the distance between two point charges?
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What is the effect of permittivity on the electrostatic force between two charges?
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What is the direction of the electrostatic force between two point charges?
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What is an electric field?
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What is an electric field line?
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What is the electric field strength (𝑬) at a point in an electric field?
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What is the unit of electric field strength?
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What does the electric field strength (𝑬) of an electric field describe?
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Study Notes
Electric Charge
- Electric Charge (Q or q) is a measure of whether a body has more or less electrons than protons.
- The unit of electric charge is the coulomb (C).
Atomic Structure
- An atom is composed of three main particles: protons, neutrons, and electrons.
- Protons and neutrons are located in the nucleus (centre of the atom), while electrons orbit around it.
Forces between Charges
- Like charges (i.e., two positive charges or two negative charges) repel each other.
- Unlike charges (i.e., one positive charge and one negative charge) attract each other.
Charging by Friction
- Rubbing cloth against Polythene causes the Polythene to become negatively charged.
- Rubbing cloth against Perplex causes the Perplex to become positively charged.
- This method can be used to demonstrate the forces between charges.
Electric Charge
- Electric Charge (Q or q) is a measure of whether a body has more or less electrons than protons.
- The unit of electric charge is the coulomb (C).
Atomic Structure
- An atom is composed of three main particles: protons, neutrons, and electrons.
- Protons and neutrons are located in the nucleus (centre of the atom), while electrons orbit around it.
Forces between Charges
- Like charges (i.e., two positive charges or two negative charges) repel each other.
- Unlike charges (i.e., one positive charge and one negative charge) attract each other.
Charging by Friction
- Rubbing cloth against Polythene causes the Polythene to become negatively charged.
- Rubbing cloth against Perplex causes the Perplex to become positively charged.
- This method can be used to demonstrate the forces between charges.
Electric Charge and Conductors
- A conductor is a substance that allows electric charge to flow through it.
- An insulator is a substance that prevents electric charge from flowing through it.
Static Charge on Conductors
- Static charges are always found on the outer surface of a conductor.
- On a conductor, static charge tends to accumulate at the pointed regions.
- This is because the charge density is higher at pointed areas, resulting in a stronger electric field.
Point Discharge
- Point discharge occurs at very sharp points due to high charge density.
- At these points, a strong electric field is created, attracting and repelling ions.
- This ultimately neutralizes the object, as demonstrated by the 'electric wind' effect on a naked flame.
Gold Leaf Electroscope
- Used to detect small charges, estimate the size of a charge, identify the sign of the charge, and distinguish between a conductor and insulator.
- Consists of multiple components, including a thin gold leaf placed close to a metal rod.
- When the gold leaf and metal rod have the same sign of charge, they repel each other.
Coulomb's Law
- The force between two point charges is proportional to the product of their charges and inversely proportional to the square of the distance between them.
- The formula for Coulomb's Law is F = Q1Q2/4πEd^2, where F is the force in newtons (N).
- This formula is an example of an inverse square law.
- The size of the force is the same on each body, and the force is along the line between them.
Electrostatic Force
- One of the factors affecting the size of the electrostatic force is the permittivity (ε) of the medium surrounding the charges.
- The permittivity and force are inversely proportional.
- The force is greatest when the charges are in a vacuum, where the permittivity is low.
Electric Fields
- An electric field is a region of space where a static electric charge experiences a force other than gravity.
Key Characteristics
- An electric field line is the path a positive charge would follow if placed in the electric field.
Electric Field Strength
- Electric field strength (𝑬) is the force per unit positive charge at a point in the electric field.
- Measured in newton per coulomb (N C-1) or volt per meter (V m-1).
Note: 𝑬 is the symbol for electric field strength.
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Description
Learn about electric charge, its unit, and the structure of an atom, including the forces between charges.
