Question 1

Definition check — what is an element? Choose the most accurate definition of an element from basic chemistry.

Accepted Answer

Introduction / Context: In foundational chemistry, precise definitions help avoid misconceptions that cascade into errors about bonding, compounds, and mixtures. The term “element” is central to classifying matter. Given Data / Assumptions: We are choosing among definitions, not examples. We assume standard IUPAC-style terminology for element, compound, and mixture. Concept / Approach: An element is a pure substance consisting of only one type of atom, characterized by a unique number of protons (atomic number). Elements can exist in various physical states and allotropic forms (e.g., O2, O3) but remain composed exclusively of atoms of that element. Compounds comprise two or more different elements bonded in definite proportions; mixtures combine substances physically without fixed ratios. Step-by-Step Solution: Identify the defining feature: atomic identity (same atomic number).Match to the option expressing “only one kind of atom.”Reject statements about charge, mixtures, or natural occurrence that do not define what an element is. Verification / Alternative check: Periodic table entries represent elements; samples like copper wire or sulfur crystals contain only Cu or S atoms, respectively, regardless of form. Why Other Options Are Wrong: Always electrically charged: elements can be neutral or ionized; charge state does not define “element.” Mixture of compounds: describes mixtures, not elements. Found only in pure form in nature: many elements occur as minerals or combined states; purity is not required in nature. Common Pitfalls: Confusing a chemical element with a pure sample; impurities do not change elemental identity. Final Answer: A substance made of only one kind of atom

Question 2

Fluid–electrical analogy — a pump corresponds to which electrical component? When comparing a fluid system to an electrical circuit, the fluid pump is analogous to which component?

Accepted Answer

Introduction / Context: Analogies between fluid mechanics and circuit theory help intuition: pressure ↔ voltage, volumetric flow rate ↔ current, resistance to flow ↔ electrical resistance. Identifying component analogs clarifies system behavior. Given Data / Assumptions: Pump adds mechanical energy to the fluid, raising pressure head. Battery provides electromotive force, raising electrical potential. We compare roles rather than physical construction. Concept / Approach: In the analogy, pressure difference drives flow just as voltage drives current. A pump increases pressure head, creating a driving potential; a battery increases electric potential (EMF), driving current through the circuit. Conductors and lamps primarily dissipate or carry current; insulators block it. Therefore, the correct analog to the energy-adding device is a battery (or ideal voltage source). Step-by-Step Solution: Map fluid variables to electrical: ΔP ↔ V, Q ↔ I.Identify the device that creates ΔP: the pump.Identify the electrical device that creates V: the battery.Select battery as the analog. Verification / Alternative check: Network analogies in process control textbooks show pump symbols paired with voltage sources in equivalent circuits. Why Other Options Are Wrong: Conductor: analog to low hydraulic resistance (wide pipe), not an energy source. Lamp: dissipative load (resistor); no pressure or voltage generation. Insulator: analog to a closed valve or blocked pipe. Common Pitfalls: Confusing a pump with a current source; the standard mapping is pump ↔ voltage source for constant head, though current-source analogs are sometimes used in advanced treatments. Final Answer: Battery (voltage source)

Question 3

Circuit symbols — which description matches the battery symbol? Choose the correct verbal description of the standard battery symbol used in circuit diagrams.

Accepted Answer

Introduction / Context: Electronic schematics rely on standardized symbols to communicate quickly across disciplines. Recognizing the battery symbol prevents wiring errors and aids troubleshooting. Given Data / Assumptions: Conventional schematic conventions are used (IEC/ANSI). Battery symbol is an array of one or more cells. Concept / Approach: A battery symbol consists of adjacent pairs of parallel lines representing cells. Within each pair, the longer line represents the positive plate/terminal and the shorter line represents the negative. Multiple pairs in series depict a multi-cell battery. This is distinct from symbols for resistors (zigzag or rectangle), variable sources, or diodes/transistors (triangle forms). Step-by-Step Solution: Recall that cell polarity is indicated by unequal line lengths.Recognize multiple pairs indicate more than one cell in series.Match this description to the correct option. Verification / Alternative check: Any introductory electronics reference confirms the longer line as positive and the shorter as negative in the battery/cell symbol. Why Other Options Are Wrong: Zigzag: resistor, not a source. Circle with arrow: commonly used for transducers or adjustable sources, not the standard battery symbol. Opposing triangles: resembles a generic amplifier/diode-like depiction, not a battery. Common Pitfalls: Reversing polarity by assuming the shorter line is positive; this is incorrect. Final Answer: Two parallel lines of unequal length; the longer line denotes positive terminal and the shorter line denotes negative

Question 4

Electrical quantities — correct SI unit and symbol for electric current What are the SI unit and the standard symbol used to denote electric current?

Accepted Answer

Introduction / Context: Using correct SI units and symbols is essential for clear communication in engineering calculations and schematics. Electric current has a defined base unit and a standard symbol in the International System of Units (SI). Given Data / Assumptions: We are asked for both the SI unit name and the printed unit symbol. We distinguish between unit symbols and variable symbols used in equations. Concept / Approach: The SI base unit of current is the ampere with symbol A. In circuit equations, current is often denoted by the variable i or I, but the official unit symbol remains A. Coulomb (C) is the unit of electric charge, not current; Q commonly denotes charge, not current. Step-by-Step Solution: Identify the SI base unit for current: ampere.Confirm the unit symbol: A.Distinguish variable symbols (I, i) from unit symbols; select Ampere, A. Verification / Alternative check: SI Brochure lists ampere (A) as the base unit; Coulomb equals amperesecond (C = As). Why Other Options Are Wrong: Coulomb, I: Coulomb measures charge, not current. Ampere, Q: Q is used for charge, not the unit symbol for current. Ampere, I: I is a variable symbol in equations, not the SI unit symbol. Common Pitfalls: Mixing up variable notation (I) with SI unit symbol (A). Final Answer: Ampere, A

Question 5

Structure of matter — the basic building blocks All matter is fundamentally composed of which set of subatomic particles?

Accepted Answer

Introduction / Context: Atomic theory explains material behavior, bonding, and physical properties. Recognizing the fundamental subatomic particles anchors further study in chemistry and physics. Given Data / Assumptions: We refer to ordinary matter, ignoring deeper constituents like quarks for introductory level. Atoms consist of a nucleus and an electron cloud. Concept / Approach: The atom comprises a positively charged nucleus with protons (positive) and neutrons (neutral), surrounded by negatively charged electrons. Ion formation results from gain or loss of electrons but does not introduce new fundamental particle types beyond these three at this level. Step-by-Step Solution: Identify core subatomic particles: proton, neutron, electron.Exclude fixed ratios like “two protons per neutron/electron” which are not general truths.Exclude “charged ions” since ions are atoms/molecules with net charge, not fundamental particles. Verification / Alternative check: All elements in the periodic table are defined by proton number; isotopes differ by neutron number; chemistry is governed by electron configuration. Why Other Options Are Wrong: Two protons per neutron or electron: no universal ratio exists across elements and isotopes. Electrons, neutrons, and charged ions: ions are composite entities, not elementary constituents. Common Pitfalls: Confusing ions (charged atoms or molecules) with subatomic particles. Final Answer: Electrons, neutrons, and protons

Question 6

Basic component function — what does an electrical switch do? Choose the statement that best describes the function of a switch in a circuit.

Accepted Answer

Introduction / Context: Switches are ubiquitous control devices in electrical systems. Understanding their basic function is essential before delving into variants like SPST, DPDT, and momentary types. Given Data / Assumptions: We consider the generic definition of a switch, independent of form factor. “Open” means an intentional break; “close” means completing the circuit. Concept / Approach: A switch is a controllable conductive path interrupter. In the open position, it creates an infinite (or very high) resistance break, stopping current. In the closed position, it provides a low-resistance path, allowing current to flow. Other attributes (poles, throws, fuse holders) are features of specific devices, not the fundamental definition. Step-by-Step Solution: Define the function: connect or disconnect the circuit actively.Map to the most general statement among options.Select the choice that says “opens or completes a current path.” Verification / Alternative check: Standards and catalogs define switches by their contact arrangements but always as devices to make/break circuits. Why Other Options Are Wrong: Short circuits complex circuits: a properly used switch does not short; it controls conduction intentionally. Holds a fuse: that is the role of a fuse holder, not a switch. Has double poles: some switches do, but that is not definitional. Common Pitfalls: Confusing specialized switch features with the core function. Final Answer: Opens or completes a current path

Question 7

Fundamentals of matter in physical science: In basic physics and chemistry, matter can exist in which principal states under ordinary conditions?

Accepted Answer

Introduction / Context: This question checks core understanding of how matter presents itself in everyday physical science. Recognizing the common states establishes a foundation for later topics such as phase change, thermodynamics, and materials engineering. Given Data / Assumptions: The focus is on principal states encountered in school science and general engineering. Extreme or exotic states like plasma or Bose–Einstein condensate are beyond the basic scope unless specifically asked. Concept / Approach: Matter typically exists as solid, liquid, or gas depending on temperature and pressure. In solids, particles are closely packed with fixed shape and volume; in liquids, particles are close but can flow with fixed volume and variable shape; in gases, particles are far apart with neither fixed shape nor fixed volume. Step-by-Step Solution: Identify the three principal states commonly taught: solid, liquid, gas.Scan the options for this exact trio in any order.Select the choice that lists solid, gas, or liquid together. Verification / Alternative check: If a substance is heated or cooled at standard pressure, it transitions among these three states via melting, freezing, vaporization, condensation, and sublimation; this confirms the three principal states. Why Other Options Are Wrong: Solid, liquid, or mineral: mineral is a material category, not a state of matter. Mineral, gas, or liquid: same issue; mineral is not a state. Plastic, solid, or gas: plastic is a class of polymers, not a thermodynamic state. Plasma, condensate, or crystal only: plasma and condensate are exotic states; crystal refers to structure within a solid, not a separate state. Common Pitfalls: Confusing material classes (metals, plastics, minerals) with physical states; mixing structure descriptors like crystalline or amorphous with states. Final Answer: solid, gas, or liquid

Question 8

Electrical measurements – Core instrument function: An ammeter is designed and connected in a circuit to measure which electrical quantity?

Accepted Answer

Introduction / Context: In basic electrical engineering, each instrument has a specific purpose. Understanding what an ammeter measures is fundamental to safe and correct circuit testing and troubleshooting. Given Data / Assumptions: Standard passive or digital ammeter is considered. Conventional connection method: series insertion in the circuit branch. Ideal ammeter has negligible internal resistance. Concept / Approach: Current is the rate of flow of electric charge through a conductor. An ammeter must be placed in series so that the branch current passes through the meter. Its internal resistance must be very low to minimize voltage drop and avoid altering the circuit behavior. Step-by-Step Solution: Identify the electrical quantity associated with series measurement and low internal resistance: current.Select the option that states current. Verification / Alternative check: Contrast with a voltmeter that is connected in parallel across elements and has high internal resistance to measure voltage without drawing significant current. An ohmmeter measures resistance and must not be connected to a live circuit. Why Other Options Are Wrong: Voltage: measured by a voltmeter in parallel, not by an ammeter. Resistance: measured by an ohmmeter or multimeter in resistance mode. All of the above: a single-purpose ammeter does not measure multiple quantities simultaneously. Power: requires voltage and current; not a direct ammeter reading alone. Common Pitfalls: Connecting an ammeter across a source directly, which can cause a short circuit due to very low meter resistance. Final Answer: Current

Question 9

Electrochemical energy systems – Battery vs. fuel cell: How does a conventional battery fundamentally differ from a fuel cell in operation and design?

Accepted Answer

Introduction / Context: Batteries and fuel cells both convert chemical energy to electrical energy, but their architectures and sources of reactants differ. This distinction affects applications from portable devices to vehicles and grid storage. Given Data / Assumptions: Batteries contain their active materials internally. Fuel cells receive fuel and oxidant from external supplies. No specific chemistry (lead acid, Li-ion, PEMFC, SOFC) is mandated by the question. Concept / Approach: A battery is generally a closed or self-contained system: its electrodes and electrolyte hold the necessary reactants. When discharged, internal reactants are consumed and require recharging or replacement. A fuel cell is an open system: it continuously generates electricity while fuel and oxidant are fed from outside. When the feeds stop, power stops even though the cell hardware remains unchanged. Step-by-Step Solution: Identify the defining difference: internal versus external reactant supply.Select the option that states a battery is a closed system. Verification / Alternative check: Consider a car: the 12 V battery stores reactants and is recharged; a fuel cell vehicle carries hydrogen and draws oxygen from air, producing water continuously while fuel flows. Why Other Options Are Wrong: Hydrogen and oxygen use: that is characteristic of many fuel cells, not of all batteries. Polymer electrolyte membrane: specific to certain fuel cells; many batteries do not use PEM. Fuel cell storing all reactants internally: incorrect; fuel cells are designed for continuous external feed. Common Pitfalls: Assuming any device with electrodes and electrolyte is closed; the key is whether reactants are replenished externally during operation. Final Answer: A battery is a closed system

Question 10

Electric potential calculation from energy and charge: If 60 joules of energy are available for every 15 coulombs of charge moved, what is the electrical potential (voltage) between the points?

Accepted Answer

Introduction / Context: Voltage quantifies energy per unit charge in an electric field. Converting energy and charge to potential difference is a standard operation in circuit theory and electromagnetism. Given Data / Assumptions: Energy supplied, W = 60 J. Charge moved, Q = 15 C. No losses or additional sources are considered; a simple ratio applies. Concept / Approach: Voltage V between two points relates to energy and charge through the definition V = W / Q. Units check: joule per coulomb reduces to volt, which verifies dimensional consistency. Step-by-Step Solution: Write the relation: V = W / Q.Substitute values: V = 60 / 15.Compute the quotient: 60 / 15 = 4.Therefore, V = 4 V. Verification / Alternative check: Scale reasoning: If 60 J were delivered for 60 C, the voltage would be 1 V. Halving the charge to 30 C would double the voltage to 2 V. At 15 C (one quarter of 60 C), the voltage becomes 4 V, matching the calculation. Why Other Options Are Wrong: 60 V or 15 V: these would require W/Q to be 60 or 15 respectively, which is not the case. 0.25 V or 1 V: both are inconsistent with the ratio 60/15. Common Pitfalls: Confusing V = W * Q or V = Q / W; always recall voltage is energy per charge, not the product. Final Answer: 4 V

Question 11

Atomic structure – Determining atomic number: The atomic number of an atom is defined as the count of which subatomic particle in the nucleus?

Accepted Answer

Introduction / Context: The atomic number uniquely identifies a chemical element. It distinguishes elements across the periodic table and determines the arrangement of electrons in neutral atoms. Given Data / Assumptions: A neutral atom has equal numbers of protons and electrons. Neutrons may vary, producing isotopes without changing the element identity. Concept / Approach: Atomic number Z is defined as the number of protons in the nucleus. Protons carry positive charge and establish the element identity. Electron count can change in ions without altering Z. Neutron count N contributes to mass number A = Z + N, not to atomic number. Step-by-Step Solution: Recall definition: Z = number of protons.Select the option that states protons. Verification / Alternative check: Hydrogen has Z = 1 because it has one proton; carbon has Z = 6, oxygen Z = 8, etc. Isotopes like C-12 and C-14 differ in neutrons but both have Z = 6. Why Other Options Are Wrong: Electrons: vary in ions; not the defining number. Neutrons or protons plus neutrons: define isotopes and mass number, not element identity. Neutrons minus protons: not a standard definition. Common Pitfalls: Confusing atomic number with mass number; forgetting that ions still retain the same atomic number as the neutral atom of the element. Final Answer: Protons

Question 12

Basic DC circuit composition: A minimal practical electric circuit requires which set of components to operate and deliver useful work?

Accepted Answer

Introduction / Context: Identifying the minimal set of elements for a functioning circuit is crucial for design, analysis, and troubleshooting. A circuit must provide energy, a path for charge movement, and a place where energy is converted to useful form. Given Data / Assumptions: Direct current example, but the logic applies to AC as well. Load represents any device that converts electrical energy to another form. Conductive path is continuous and closes the loop. Concept / Approach: A circuit requires: (1) a source of electromotive force, (2) a closed conducting loop, and (3) a load that consumes power. Without any of these, current will not flow usefully: no source means no motive force, an open path means no current, and no load means no purposeful energy conversion. Step-by-Step Solution: Identify the energy provider: voltage source.Ensure a closed path exists: wires or traces forming a complete loop.Include a load: resistor, lamp, motor, or electronics that utilize the energy. Verification / Alternative check: Power balance: P = V * I is dissipated in the load. If the loop is open, I = 0; if there is no source, V = 0; if there is no load, power is not usefully consumed. Why Other Options Are Wrong: Load, resistor, path: missing the source; a resistor is one type of load, so the list is incomplete and redundant. Source, path, and a battery: battery is a source; this duplicates the source and omits the load. Path, battery, copper wire: lacks an explicit load; wire is part of the path. Switch, inductor, fuse: none provides a driving source or guaranteed load. Common Pitfalls: Assuming any component trio makes a circuit; forgetting the loop closure requirement. Final Answer: A voltage source, a load, and a conductive path for current

Question 13

Charge signs in atomic particles: By convention, which particles carry the negative and positive electric charge, respectively (in that order)?

Accepted Answer

Introduction / Context: Charge sign conventions underpin circuit theory and particle physics. Correctly assigning negative and positive charges is essential for understanding current direction, electric fields, and chemical bonding. Given Data / Assumptions: Elementary particles considered: electron, proton, neutron. Conventional current direction is from positive to negative terminal, opposite to electron flow. Concept / Approach: Electrons carry a single negative elementary charge, while protons carry a single positive elementary charge. Neutrons are electrically neutral. The atom as a whole may be neutral or an ion depending on electron count, but charge signs belong to the particles themselves. Step-by-Step Solution: Identify the negative charge carrier among fundamental particles: electron.Identify the positive charge carrier: proton.Match the required order: negative then positive. Verification / Alternative check: Electrostatics experiments and mass spectrometry both confirm the charges of electrons and protons; neutron has no net charge. Why Other Options Are Wrong: Proton and electron: order reversed relative to the question. Atom and nucleus / electron and element: categories are mismatched; element is not a particle. Neutron and proton: neutron is neutral, not negative. Common Pitfalls: Confusing conventional current direction with electron flow direction. Final Answer: Electron and proton

Question 14

Chemical classification – What do we call a substance formed by chemically combining different elements in fixed proportions?

Accepted Answer

Introduction / Context: Distinguishing elements, compounds, molecules, and mixtures is a foundational chemistry competence. This classification influences properties, separation methods, and reaction behavior. Given Data / Assumptions: The material contains two or more different elements. Combination is chemical, forming a new substance with fixed composition. Concept / Approach: A compound is a pure substance made when elements chemically bond in definite ratios, producing properties different from the constituent elements. A molecule is a structural unit that can represent either an element (e.g., O2) or a compound (e.g., H2O). A mixture combines substances physically without fixed ratios and without chemical bonding. Step-by-Step Solution: Identify whether the description implies chemical bonding and fixed composition.Chemical bonding in fixed ratios leads to the term compound.Select the option stating compound. Verification / Alternative check: Water is a compound of hydrogen and oxygen in a 2:1 ratio by atoms. Brass is a mixture (alloy) of copper and zinc with variable composition, confirming the compound versus mixture distinction. Why Other Options Are Wrong: Element: consists of one type of atom. Ion: an atom or molecule with net charge. Molecule: structural term that may not imply different elements or fixed stoichiometry when used alone. Mixture: lacks chemical bonding and fixed ratio. Common Pitfalls: Calling any multi-atom species a compound; remember molecules of an element exist (e.g., N2) that are not compounds. Final Answer: A compound

Question 15

Resistor color coding (4-band) practice: What is the correct color code for a 220 Ω, 5% tolerance resistor?

Accepted Answer

Introduction / Context: Color coding allows quick identification of resistor values without reading tiny printed numbers. The standard 4-band code uses two significant digits, a multiplier, and a tolerance band. Given Data / Assumptions: Target resistance: 220 ohms. Tolerance: 5 percent. Standard 4-band E12 or E24 series coding. Concept / Approach: Digit colors: Black 0, Brown 1, Red 2, Orange 3, Yellow 4, Green 5, Blue 6, Violet 7, Gray 8, White 9. Multiplier band is 10^n with the same color mapping. Gold indicates 5 percent tolerance, silver indicates 10 percent. Step-by-Step Solution: Write 220 in significant-digit and multiplier form: 22 * 10^1.First band (2): Red.Second band (2): Red.Multiplier (10^1): Brown.Tolerance (5%): Gold. Verification / Alternative check: A quick check: Red-Red-Black would be 22 * 10^0 = 22 Ω, which is not correct. Red-Red-Brown yields 220 Ω, matching the requirement, and gold is the correct 5 percent tolerance band. Why Other Options Are Wrong: Orange, Orange, Black, Gold: 33 * 10^0 = 33 Ω. Red, Red, Black, Gold: 22 Ω, not 220 Ω. Red, Red, Brown, Silver: 220 Ω but 10 percent tolerance, not the specified 5 percent. Brown, Black, Brown, Gold: 10 * 10^1 = 100 Ω, incorrect value. Common Pitfalls: Mixing up the multiplier band with a third significant digit and confusing tolerance colors gold versus silver. Final Answer: Red, Red, Brown, Gold

Question 16

Electrochemical cells – Primary vs. secondary sources: A secondary cell produces direct current via chemical reactions; a primary cell generates direct current by which process?

Accepted Answer

Introduction / Context: Both primary and secondary cells are galvanic devices that convert chemical energy into electrical energy. The key difference lies in reversibility: secondary cells are rechargeable, while primary cells are intended for single-use discharge. Given Data / Assumptions: The statement already notes that a secondary cell generates DC through chemistry. We compare the mechanism of primary cells to confirm it is the same fundamental process. Concept / Approach: Primary cells (zinc–carbon, alkaline) and secondary cells (lead–acid, nickel–metal hydride, lithium-ion during discharge) both generate electromotive force due to spontaneous redox reactions at their electrodes. In primary cells, the reactions are not designed to be efficiently reversible; in secondary cells, charging reverses the chemistry. Step-by-Step Solution: Identify the source of EMF in galvanic cells: redox chemistry.Recognize that both primary and secondary cells use chemical reactions to produce DC.Select the option that states chemically. Verification / Alternative check: Observe that no purely electrical process inside a passive cell can sustain DC output without a chemical or physical energy source; heat or light can drive separate devices (thermopiles, photovoltaics) but those are not primary batteries. Why Other Options Are Wrong: Electrically: electricity is the output, not the internal energy source. Thermally: thermoelectric devices differ from chemical cells. Optically: photovoltaic cells produce DC from light, not considered primary chemical cells. Mechanically: generators convert mechanical to electrical energy, not battery operation. Common Pitfalls: Confusing the discharge mechanism with the recharge mechanism; only secondary cells accept electrical energy to reverse chemistry during charging. Final Answer: Chemically

Question 17

In basic atomic physics, which of the following is the smallest fundamental entity when comparing an atom and its subatomic constituents (proton, neutron, and electron)?

Accepted Answer

Introduction / Context: This question checks foundational understanding of atomic structure and scale. An atom is composed of a dense nucleus (protons and neutrons) surrounded by electrons. Knowing which is smallest helps learners anchor later topics like spectroscopy, semiconductor physics, and chemical bonding. Given Data / Assumptions: Compare the relative sizes and masses of atom, proton, neutron, and electron. Standard model context: electron is treated as a pointlike lepton with extremely small effective size in atomic physics. No exotic particles are considered—only the items listed. Concept / Approach: Size and mass trends are decisive. The atom's diameter is on the order of 10^-10 m due to the electron cloud. Protons and neutrons are nucleons with characteristic sizes ~10^-15 m and masses roughly 1836 and 1839 times the electron's mass, respectively. The electron has far smaller mass and, in non-relativistic atomic models, is considered pointlike compared to nucleons and atoms. Step-by-Step Solution: Compare atom vs subatomic particles: the atom is vastly larger because it includes electron orbitals/cloud.Compare nucleons vs electron: proton/neutron are composite (quarks) and much heavier.Electron has the least mass and no internal structure in the model used here; thus it is the smallest among the options. Verification / Alternative check: Typical mass values: m_e ≈ 9.11×10^-31 kg; m_p ≈ 1.67×10^-27 kg; m_n ≈ 1.67×10^-27 kg. Orders-of-magnitude differences confirm the electron as smallest by mass and effective size in atomic physics. Why Other Options Are Wrong: Atom: much larger than any subatomic component. Proton / Neutron: both are far heavier and larger in scale than the electron. Common Pitfalls: Confusing mass with charge magnitude; assuming the positively charged proton is "smaller" because it resides in the tiny nucleus—size here refers to particle scale, not electric charge. Final Answer: electron

Question 18

Electrostatics and units: one coulomb of charge corresponds to approximately how many elementary charges (electrons) in magnitude?

Accepted Answer

Introduction / Context: Electrical charge is quantized in units of the elementary charge e. Relating the SI unit coulomb (C) to the number of electrons builds intuition for circuit analysis, capacitor charge storage, and semiconductor doping levels. Given Data / Assumptions: Elementary charge magnitude: e ≈ 1.602 × 10^-19 C. One coulomb is the total charge carried by many electrons. We seek a count of electrons whose total charge magnitude equals 1 C. Concept / Approach: Use the proportionality: total charge Q equals number of electrons n times elementary charge e in magnitude. That is Q = n * e. Solve for n = Q / e with Q = 1 C and e = 1.602 × 10^-19 C. Step-by-Step Solution: Write relation: n = Q / e.Substitute values: n = 1 / (1.602 × 10^-19).Compute order of magnitude: n ≈ 6.24 × 10^18 electrons. Verification / Alternative check: Check units: coulomb divided by coulomb per electron leaves a pure count. The value 6.24 × 10^18 is the standard rounded figure used in textbooks and exam tables. Why Other Options Are Wrong: 6.24 × 10^-18: inverted exponent, many orders too small. One ampere or one second: those are current and time units, not counts of charge carriers. Common Pitfalls: Mixing sign with magnitude; here we compare magnitudes, so we ignore the negative sign on electron charge. Confusing coulomb (charge) with ampere (charge per second). Final Answer: 6.24 × 10^18 electrons

Question 19

Atomic structure: removing a non-neutral subatomic particle (such as an electron) from an atom changes the atom into what kind of species?

Accepted Answer

Introduction / Context: Ion formation is central to chemistry, electrochemistry, and device physics. When an atom gains or loses electrons, its net charge changes and it behaves differently in fields, solutions, and solids. Given Data / Assumptions: Start from a neutral atom with equal protons and electrons. Removal or addition pertains to electrons in typical chemical processes. The nucleus remains the same element if the proton count is unchanged. Concept / Approach: Charge balance governs species identity: Z protons define the element, while electron count sets the charge state. Removing an electron produces a cation; adding an electron produces an anion. Changing the proton number would change the element, but that is nuclear, not ordinary chemical, change. Step-by-Step Solution: Neutral atom: protons = electrons → net charge 0.Remove an electron: protons > electrons → net positive charge → cation.Add an electron: electrons > protons → net negative charge → anion. Verification / Alternative check: Common examples: Na → Na^+ by losing one electron; Cl → Cl^- by gaining one electron. Neither process changes the nuclear charge Z, so the element identity persists. Why Other Options Are Wrong: Nucleus: refers to protons and neutrons only, not the whole ionized atom. Heavier element: element identity changes only if proton number changes. Compound: requires multiple atoms bonded; ionization alone does not create a compound. Common Pitfalls: Confusing isotope (neutron change) or element transmutation (proton change) with ionization (electron change). Final Answer: charged ion

Question 20

Electric circuits: in a metallic circuit that becomes short-circuited, what happens to the current magnitude assuming an ideal source and negligible resistance in the short?

Accepted Answer

Introduction / Context: A short circuit is a low-resistance path that bypasses the intended load. Recognizing its current implications is fundamental to selecting fuses, breakers, and wire gauges for protection. Given Data / Assumptions: Voltage source with internal resistance much smaller than the normal load. Short-circuit path of very low resistance. Ohm’s law applies: I = V / R_total. Concept / Approach: Current magnitude is inversely related to circuit resistance. When the circuit is shorted, the effective resistance plummets toward the source/internal resistance, causing current to surge well beyond the design value and potentially damaging equipment. Step-by-Step Solution: Nominal load: I_load = V / (R_source + R_load).Short-circuit: I_short = V / (R_source + R_short) with R_short ≈ 0.Since R_source ≪ R_load, I_short ≫ I_load, leading to a large current flow. Verification / Alternative check: Protective devices are rated by prospective short-circuit current (fault current), confirming that short circuits demand interrupting capacities far higher than normal operating currents. Why Other Options Are Wrong: Small/Some current: contradicts Ohm’s law under low resistance. No current: would require an open circuit, not a short. Common Pitfalls: Confusing open and short faults; assuming a source can supply infinite current—real sources limit current, but it is still very large relative to normal operation. Final Answer: a large current flow

Voltage and Current Questions