EE 40: Nature of Electricity

Questions and Answers

What is the unit of electric charge?

Coulomb (correct)

Volt

Ampere

Ohm

What occurs when an atom gains an electron?

It becomes uncharged.

It becomes an anion. (correct)

It becomes a cation.

It becomes neutral.

Which of the following describes an uncharged atom?

It has more electrons than protons.

It has equal numbers of protons and electrons. (correct)

It has no electrons.

It has more protons than electrons.

What determines whether an atom becomes a cation or anion?

The loss or gain of electrons. Signup and view all the answers

What is the relationship between electric field and electric force?

Electric fields interact with charged bodies to produce electric forces. Signup and view all the answers

What defines electrical potential difference?

The difference in electrical potential energy between two charges. Signup and view all the answers

What characterizes electropositive elements?

They lose electrons in chemical reactions. Signup and view all the answers

How many electrons are in one Coulomb of charge?

6.242 x 10^18 Signup and view all the answers

What is the primary characteristic that distinguishes an element from a compound?

An element consists of atoms of only one kind. Signup and view all the answers

In the context of atomic structure, what does the atomic number represent?

The number of protons in the nucleus of an atom. Signup and view all the answers

What is the role of electrons in an atom?

Electrons are negatively charged particles that orbit the nucleus. Signup and view all the answers

What term is used to describe the smallest part of a compound that retains all its properties?

Molecule Signup and view all the answers

How do electrons transition between orbits in the Bohr atomic model?

By absorbing or emitting energy. Signup and view all the answers

Why is the mass of an electron often neglected in atomic mass calculations?

Electrons have a relatively very small mass compared to protons and neutrons. Signup and view all the answers

What type of charge do protons carry?

Positive charge Signup and view all the answers

What is the relationship between atomic number and electron configuration in a neutral atom?

The atomic number equals the number of protons and also the number of electrons. Signup and view all the answers

What is the unit of potential difference?

Volt Signup and view all the answers

How is 1 Ampere of current defined?

The movement of one coulomb past a point in one second Signup and view all the answers

If 2 Amperes of current flow through a conductor for 1 minute, how many coulombs pass through?

120 C Signup and view all the answers

What does the current density (J) measure?

Current per unit cross-sectional area Signup and view all the answers

What type of current flows in one direction only?

Direct Current Signup and view all the answers

What is the practical unit of resistance?

Ohm Signup and view all the answers

Which of the following describes conductance?

The ability of a material to conduct electricity Signup and view all the answers

What principle explains the production of static electricity by friction?

Electrons are transferred between insulators by rubbing Signup and view all the answers

What is the maximum number of electrons that can occupy the nth shell according to the formula $N_e = 2n^2$?

2n^2 Signup and view all the answers

Which type of material has more than four valence electrons and does not allow electricity to flow easily?

Insulator Signup and view all the answers

What is required for a valence electron to escape its shell and become a free electron?

Energy equal to the energy gap Signup and view all the answers

Semiconductors are defined as materials that have how many valence electrons?

Exactly four Signup and view all the answers

In the context of atomic structure, what does the conduction band represent?

The energy level where free electrons reside Signup and view all the answers

What characterizes a conductor in terms of valence electrons?

Less than four valence electrons Signup and view all the answers

What is the forbidden band in an atom?

Region where no electrons exist Signup and view all the answers

What unit is commonly used to measure the energy gap between the valence band and the conduction band?

Electron volts (eV) Signup and view all the answers

Study Notes

Nature of Electricity

Electricity is a form of energy defined by electric charge, voltage, and current, enabling work to be done.
Electrical energy is specifically associated with electric charges.

Basic Physics Fundamentals

Elementary Particles:
- Electrons: negatively charged.
- Protons: positively charged.
- Neutrons: electrically neutral.

Structure of Matter

Matter consists of atoms, which are made up of subatomic particles (electrons, protons, and neutrons).
Elements: substances formed from identical atoms, representing the fundamental identity of materials.
Compounds: made from different atoms or elements combining.
Molecules: smallest unit of a compound retaining its properties.

Atomic Properties

Atomic Number: number of protons in an atom's nucleus; equal to electrons in a neutral atom, determining its periodic table position.
Atomic Mass: total mass of an atom, summing protons and neutrons while neglecting electron mass.

Bohr Atomic Model

Electrons orbit the nucleus in defined paths (orbits), defined by quantum numbers.
Maximum electron capacity in a shell is given by the formula: Ne = 2n².
Valence Shell: outermost shell filled with electrons; valence electrons can become free electrons leading to electrical current.

Electrical Classifications of Material

Conductors: materials with less than 4 valence electrons, allowing easy electrical flow.
Semiconductors: exactly 4 valence electrons, presenting intermediate electrical properties.
Insulators: more than 4 valence electrons, restricting electrical flow due to lack of free electrons.

Energy Bands

Energy Gap: minimum energy needed for a valence electron to become free, measured in electron volts (eV).
Valence Band: the highest energy level before conduction; contains valence electrons.
Conduction Band: where free electrons exist, having higher energy than in the valence band.
Forbidden Band: energy region between allowed bands where no electrons exist.

Coulomb (Unit of Charge)

Charged matter is influenced by elementary particles, with electric charge measured in Coulombs (C).
Coulomb Definition: 1 C = 6.242 x 10¹⁸ electrons.
Negative charge of an electron: -1.602 x 10⁻¹⁹ C; positive charge of a proton: 1.602 x 10⁻¹⁹ C.
Ion: charged atom resulting from electron loss or gain; categorized as Cation (positive) or Anion (negative).

Electric Field and Force

Charged bodies generate an electric field, which interacts with other charges, producing force and potentially causing movement.

Potential Difference

Electrical potential energy refers to a charged body's ability to do work.
Measured in volts (V); 1 V enables 1 Joule of work moving 1 Coulomb of charge.
Electromotive Force (emf): electrical force initiating the flow of charged particles.

Current

Current (I) is the flow of electrons, defined by the equation I = ΔQ / Δt (Coulombs per second).
One Ampere (A): flow of one Coulomb past a point in one second.
Current Density (J): current per unit area, measured in A/m².
Types of Current:
- Direct Current (DC): unidirectional flow.
- Alternating Current (AC): flow reverses periodically.
- Conventional Current: assumed flow from positive to negative (opposite actual flow).

Material Resistance

Resistance (R) opposes current flow, depends on material dimensions and type; measured in Ohms (Ω).
Resistance formula: R = ρ(l/A) where ρ represents resistivity.

Conductance

Conductance (G) measures the ability of a material to conduct current, inversely related to resistance, with unit Siemens (S).

Sources of Electricity

Static Electricity: occurs through friction, separating electrons to create opposite charges retained in insulators.

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Description

This quiz covers the foundational concepts of electricity, including electric charge, voltage, and current. Understanding these principles is crucial for grasping the applications of electrical energy in everyday life. Test your knowledge on the basics of electrical engineering with this quiz.