Electric Charges and Forces

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Questions and Answers

Why does rubbing a neutral object, like a pen, with a cloth cause it to attract small pieces of paper?

  • The rubbing action removes gravitational forces, leaving only electrical forces.
  • The rubbing transfers charge, leading to an imbalance of positive and negative charges on the pen. (correct)
  • The rubbing action creates new positive charges on the pen's surface.
  • The rubbing increases the mass of the pen, enhancing its gravitational attraction to the paper.

Electrostatic cling, such as chalk sticking to a blackboard, demonstrates what fundamental principle?

  • Neutral objects do not interact with charged objects until rubbed.
  • Objects with opposite charges experience an attractive force. (correct)
  • Like charges attract each other due to frictional forces.
  • Gravitational force is stronger than electrical force at close ranges.

Two initially neutral glass rods are rubbed with a silk cloth. How will the rods interact when brought close to each other?

  • They will repel each other because both rods acquire the same type of charge. (correct)
  • They will not interact because glass is an insulator.
  • They will attract each other because the silk cloth gives each rod opposite charge.
  • They will first attract and then repel as the charges equalize.

If material A is higher than material B on the electrostatic series, what will happen when they are rubbed together?

<p>Material A will become positively charged, and material B will become negatively charged. (B)</p> Signup and view all the answers

Why do electrons, rather than protons, typically transfer between objects when they are rubbed together?

<p>Protons are much heavier and reside within the nucleus, making them less mobile. (B)</p> Signup and view all the answers

How does transferring electrons to an object affect its mass?

<p>Adding electrons increases the object's mass. (C)</p> Signup and view all the answers

What concept does the elementary charge represent in the context of electric charge?

<p>The fundamental unit of charge, representing the magnitude of charge of a single electron or proton. (A)</p> Signup and view all the answers

Which of the following materials is classified as a conductor of electric charge?

<p>Drinking water. (A)</p> Signup and view all the answers

A material with high dielectric strength is best suited for which application?

<p>Preventing the flow of electric current, acting as an insulator. (C)</p> Signup and view all the answers

What does the principle of 'additivity' imply regarding electric charges?

<p>Charges can be combined algebraically, considering their signs. (D)</p> Signup and view all the answers

Why is charge considered to be 'quantized'?

<p>Charge is transferred in integer multiples of the elementary charge. (B)</p> Signup and view all the answers

What does the law of conservation of charge state?

<p>The total charge in an isolated system remains constant. (D)</p> Signup and view all the answers

A negatively charged rod is brought near a neutral metallic sphere without touching it. What happens to the charge distribution in the sphere?

<p>Electrons in the sphere accumulate on the side farther from the rod. (B)</p> Signup and view all the answers

Which of the following is NOT a typical characteristic of insulators?

<p>Free movement of electrons throughout the material. (A)</p> Signup and view all the answers

If a neutral object gains $6.25 \times 10^{12}$ electrons, what is the net charge of the object?

<p>$-1 \times 10^{-6} C$ (A)</p> Signup and view all the answers

Why charging by induction takes place without contact?

<p>The polarization of charges is made by the electric field caused by the charged object imposing a force. (C)</p> Signup and view all the answers

Two identical conducting spheres are given charges of +5q and -3q respectively. They are brought into contact and then separated. What is the charge on each sphere after separation?

<p>Each sphere has a charge of +q. (D)</p> Signup and view all the answers

A plastic rod is rubbed with wool, and the rod becomes negatively charged. What happened to the wool?

<p>It gains positive charge; the amount of negative charge gained by the rod is equal to the amount of positive charge gained by the wool. (C)</p> Signup and view all the answers

How does the electrical force between two charged objects change if the distance between them is doubled?

<p>The force is reduced to one-quarter of its original value. (A)</p> Signup and view all the answers

What is the primary reason metals are generally good conductors of electricity?

<p>They possess a large number of free electrons. (A)</p> Signup and view all the answers

Flashcards

Electric Charge

A fundamental property of matter that causes it to experience a force when near other charged matter.

Electrostatic Cling

The attraction of two objects due to opposite charges.

Neutral Object

An object with an equal amount of positive and negative charges.

Charge Interaction

Like charges repel, and unlike charges attract.

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Electrostatic Series

Predicts charge after contact; higher becomes positive, lower becomes negative.

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Electron Transfer

Losing electrons results in a positive charge, while gaining leads to negative.

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Non-Contact Charging

Causing charge in an object without direct contact.

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Electrification

The process of gaining or losing electrons.

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Electron Transfer Preference

Electrons are transferred due to their lighter mass and outer shell location.

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Mass Change by Electron Transfer

Adding electrons increases mass, removing decreases it.

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Elementary Charge

The smallest unit of charge that exists

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Conductors

Materials that allow charges to move easily.

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Insulators

Materials that resist the flow of charge.

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Dielectric Strength

Maximum electric field an insulator can withstand before conducting.

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Additivity of Charge

Charges add algebraically.

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Quantization of Charge

Charge exists in discrete multiples of elementary charge.

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Conservation of Charge

The total charge in an isolated system is constant; it is neither created nor destroyed, only transferred.

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Study Notes

Electric Charges

  • Electric charge relates to electrons.
  • It is a characteristic of particles that allows them to exert force on each other.
  • Particles of matter possess charge and exert force.

Types of Forces on Matter

  • Two types of forces act on matter: gravitational and electrical.
  • Gravitational force is due to mass.
  • Electrical force is due to charges.

Demonstrating Electric Charge

  • Rubbing a neutral object (like a pen) can cause it to attract other objects (like pieces of paper).
  • This happens because rubbing transfers charge to the object.

Electrostatic Cling

  • Electrostatic Cling is when two charges stick together because of the attractive force between them which leads to two bodies attracting.
  • An example is pieces of papers sticking to a pen after it has been rubbed

Neutrality and Charge

  • A neutral object has both positive and negative charges in equal amounts.
  • When an object is rubbed, one type of charge becomes more dominant on the surface, causing attraction or repulsion.
  • Like charges repel each other (positive-positive, negative-negative).
  • Unlike charges attract each other (positive-negative).

Gravitational vs. Electrical Force

  • Gravitational force always attracts.
  • Electrical force can attract or repel.

Everyday Examples of Electric Charges

  • Chalk sticking to a blackboard is an example of electrostatic cling.
  • Frictional force is caused by electrostatic cling between surfaces that are in contact

Charging by Rubbing

  • Scientists experimented with glass and plastic rods to understand charges.
  • Rubbing two glass rods together caused them to repel.
  • Rubbing two plastic rods together also caused them to repel.
  • But rubbing a glass rod and a plastic rod together caused them to attract.
  • It was deduced that there are different charges; those that repel and those that attract.

Naming of Charges

  • Charges were termed positive and negative because they can cancel each other out, resulting in a neutral state.

Electrostatic Series

  • Electrostatic Series can predict the charge of materials from contact charging (example rubbing).
  • When two materials are rubbed together, the material higher in the series becomes positively charged, and the lower one becomes negatively charged.
  • Example: rubbing silk and plastic together causes the silk to become positive and the plastic to become negative

Charge Through Electron Transfer

  • Positive charge results when electrons are removed.
  • Negative charge results from a surplus of electron
  • This usually happens through rubbing

Non-Contact Charging

  • A charged object can induce a charge in a nearby object without direct contact.
  • For example, bringing a negatively charged pen near paper causes the positive charges in the paper to move to the surface closest to the pen, resulting in attraction.

Electrification

  • Electrification, also known as acquiring charge, occurs when an object gains or loses electrons (and therefore gains an electrical charge).

Electron vs Proton transfer

  • Electrons, not protons, are transferred because: -Protons are much heavier than electrons (approximately 1837 times heavier). -Protons are located within the atom's nucleus, making them harder to move around than electrons which are on the outer shell.

Effect of Electron Transfer on Mass

  • Transferring electrons affects an object's mass.
  • Adding electrons increases mass.
  • Removing electrons decreases mass.
  • The mass of an electron is 9.1 x 10^-31 kg.

Elementary Charge

  • The charge of an electron is 1.6 × 10^-19 Coulombs
  • Also known as elementary charge
  • It is fundamental - it cannot be divided further

Conductors vs. Insulators

  • Conductors are materials that allow charges to move freely.
  • Examples of conductors include metals, drinking water, and the human body.
  • Insulators are materials that do not allow charges to move freely.
  • Examples of insulators include non-metals, pure water, plastic, and wood.

Resistance

  • Conductors have less resistance
  • Insulators have high resistance

Dielectric Strength

  • Dielectric strength is the maximum electric field that a material can withstand before becoming conductive.
  • Essentially, the point a material stops isolating which is the Breakout Point

Basic Properties of Electric Charge

  • Additivity
    • Charges are scalar quantities and can be added using simple algebra.
  • Quantization
    • Charge is not continuous but discrete.
    • Charge is transferred in integer multiples of the elementary charge (quantized).
  • Conservation
    • Charge can neither be created nor destroyed, only transferred
    • Total charge in an isolated system remains constant.

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