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Questions and Answers

A toaster operates at 120V and draws a current of 9.60A for 2.50 minutes. What quantity of charge, in Coulombs, passes through the toaster during this time?

  • 172,800 C
  • 1,440 C (correct)
  • 0.85 C
  • 5.67 x 10^-3 C

What happens to the electric current in a conductor if the quantity of charge passing a given point increases while the time interval remains constant?

  • The electric current decreases.
  • The electric current increases. (correct)
  • The electric current remains the same.
  • The electric current fluctuates unpredictably.

If a current of 0.55 A flows through a conductor for 12 minutes, what is the total charge, in Coulombs, that has passed through a specific point in the conductor?

  • 900 C
  • 0.0076 C
  • 6.6 C
  • 396 C (correct)

A circuit has a direct current (DC). Which statement accurately describes the movement of electrons in this type of circuit?

<p>Electrons flow in one direction only. (C)</p> Signup and view all the answers

A toaster converts electrical energy into heat and light. If 1,440 C of charge passes through the toaster at a voltage of 120V, what amount of electrical energy, in Joules, is converted?

<p>172,800 J (B)</p> Signup and view all the answers

In electrical circuits, what distinguishes 'conventional current' from 'electron flow'?

<p>Conventional current is the flow of positive charge, while electron flow is the movement of negative charge. (B)</p> Signup and view all the answers

If the cross-sectional area of a conductor increases while the water pressure (voltage) remains the same, how does this affect the flow of electric current, according to the water model analogy?

<p>The electric current increases. (A)</p> Signup and view all the answers

Benjamin Franklin's early model of electricity incorrectly suggested what about electrical charge?

<p>Excess electricity is positive, and a deficit is negative. (B)</p> Signup and view all the answers

In a home electrical system operating at 120.0 volts, a device draws 10.0 A of current. If the device is used for 3.0 minutes, how much charge passes through it?

<p>1800.0 C (C)</p> Signup and view all the answers

What significant contribution did Alessandro Volta make to the study of electric current?

<p>He invented the electrochemical cell. (C)</p> Signup and view all the answers

A wire carries a current of 2.0 A. How long will it take for 12.0 C of charge to pass through a point in the wire?

<p>6.0 seconds (B)</p> Signup and view all the answers

Suppose you double both the amount of charge passing through a conductor and the time interval over which it passes. What happens to the electric current?

<p>It remains the same. (B)</p> Signup and view all the answers

What discovery did J.J. Thomson make that refined the understanding of electric current?

<p>He discovered the electron as a negatively charged particle. (D)</p> Signup and view all the answers

A light bulb and a small fan are connected in a simple series circuit with a DC power source. If the light bulb is removed from the circuit, what is the most likely immediate effect on the fan?

<p>The fan will stop spinning because the circuit is broken. (B)</p> Signup and view all the answers

In a simple circuit, if the current is flowing from the cathode to the anode, what type of flow is occurring?

<p>Electron flow (D)</p> Signup and view all the answers

A wire initially carries a current $I$. If the charge carriers' drift velocity doubles while the number of charge carriers per unit volume is halved, and all other parameters remain constant, what is the new current?

<p>$I$ (D)</p> Signup and view all the answers

In a circuit with both series and parallel components, what is the correct placement for an ammeter and a voltmeter to measure the current through and the voltage across a specific resistor?

<p>Ammeter in series with the resistor; voltmeter in parallel with the resistor. (C)</p> Signup and view all the answers

In a complex circuit, you need to measure the potential difference drop across three different resistors. How many voltmeters are required and how should they be connected?

<p>Three voltmeters, each connected in parallel with one of the resistors. (C)</p> Signup and view all the answers

If you need to measure the total current flowing into a parallel section of a circuit, where should a single ammeter be placed?

<p>Before the point where the parallel section begins, in the main line. (C)</p> Signup and view all the answers

What is the primary reason electrical resistance occurs in a conductor?

<p>The frictional forces that oppose the motion of electrons. (A)</p> Signup and view all the answers

How does the cross-sectional area of a conductor affect its electrical resistance?

<p>Resistance is inversely proportional to the cross-sectional area. (A)</p> Signup and view all the answers

Which of the following describes electrical resistance?

<p>The opposition a material offers to the flow of electric current. (A)</p> Signup and view all the answers

A circuit contains a resistor. You measure a voltage drop of 12V across it and a current of 2A flowing through it. What is the resistance of the resistor?

<p>6 Ohms (A)</p> Signup and view all the answers

What is the role of resistivity ($$\rho$) in the formula for electrical resistance?

<p>It is the proportionality constant that depends on the material of the conductor. (B)</p> Signup and view all the answers

In a circuit with multiple resistors, how does the overall resistance change when resistors are added in series, assuming all other parameters remain constant?

<p>The overall resistance increases. (A)</p> Signup and view all the answers

A copper wire's resistance is found to be higher than expected. Which factor could most likely contribute to this discrepancy, assuming accurate measurements?

<p>The wire's temperature is higher than the reference temperature. (D)</p> Signup and view all the answers

If a voltmeter is inadvertently connected in series with a low-resistance component in a circuit, what is the likely outcome?

<p>The voltmeter reading will be very low, and the circuit current will be greatly reduced. (A)</p> Signup and view all the answers

If you double the length of a wire and halve its cross-sectional area, by what factor does its resistance change?

<p>Quadruples (D)</p> Signup and view all the answers

Which of the following changes will always result in a decrease in the resistance of a metal wire?

<p>Decreasing the length and increasing the cross-sectional area (D)</p> Signup and view all the answers

Two wires made of the same material have the same resistance. Wire A is twice as long as Wire B. How does the cross-sectional area of Wire A compare to Wire B?

<p>Wire A has twice the cross-sectional area of Wire B. (D)</p> Signup and view all the answers

A wire has a resistance of 10 $\Omega$. If the wire is stretched to three times its original length, assuming the volume remains constant, what will be the new resistance?

<p>90 $\Omega$ (D)</p> Signup and view all the answers

A student needs to select a wire for a heating element that requires high resistance. Which combination of properties would be most suitable?

<p>High resistivity, long length, small cross-sectional area. (D)</p> Signup and view all the answers

A circuit has a current of 2.5 A flowing through it for 10 minutes. Calculate the number of electrons that have passed through a specific point in the circuit during this time, given that the elementary charge is $1.602 \times 10^{-19}$ C.

<p>$9.36 \times 10^{20}$ electrons (C)</p> Signup and view all the answers

In a simple circuit containing a resistor and a power source, how should an ammeter be connected to accurately measure the current flowing through the resistor?

<p>In series with the resistor to measure the electron flow. (D)</p> Signup and view all the answers

Why is it essential to connect an ammeter in series with a circuit component when measuring electric current?

<p>To minimize the impact of the ammeter's internal resistance on the circuit's overall resistance. (A)</p> Signup and view all the answers

What is the primary difference between an ammeter and a milliammeter in measuring electric current?

<p>An ammeter measures current in amperes, while a milliammeter measures current in milliamperes (one-thousandth of an ampere). (D)</p> Signup and view all the answers

What happens to a circuit if an ammeter is removed from its series connection while the circuit is operating?

<p>The circuit becomes an open circuit, stopping the flow of current. (A)</p> Signup and view all the answers

If you have a multimeter, how would you configure it to measure the current flowing through a resistor in a circuit?

<p>Set it to measure current (as an ammeter) and connect it in series with the resistor. (D)</p> Signup and view all the answers

In a circuit diagram, what symbol represents an ammeter?

<p>A circle with an 'A' inside. (D)</p> Signup and view all the answers

What is the impact of an ideal ammeter on the overall resistance of the circuit it is connected to?

<p>It has negligible impact on the circuit's resistance. (C)</p> Signup and view all the answers

What is the net charge on an object that has $6.0 \times 10^{12}$ more protons than electrons, given the elementary charge $e = 1.602 \times 10^{-19} C$?

<p>$9.61 \times 10^{-7} C$ (C)</p> Signup and view all the answers

A small sphere has a charge of $-8.0 \times 10^{-6} C$ due to an excess of electrons. How many excess electrons are present on the sphere, given the elementary charge $e = 1.602 \times 10^{-19} C$?

<p>$5.0 \times 10^{13}$ electrons (B)</p> Signup and view all the answers

Which of the following best describes the flow of electric current in a closed circuit containing a battery and a resistor?

<p>Electrons flow from the negative terminal to the positive terminal of the battery. (D)</p> Signup and view all the answers

In an electric circuit, what is the significance of an open switch?

<p>It causes a break in the circuit, preventing current flow. (A)</p> Signup and view all the answers

A wire carries a constant current of 2.0 A. How many electrons pass through a cross-section of the wire in 5.0 seconds?

<p>$6.25 \times 10^{18}$ (A)</p> Signup and view all the answers

A certain lightbulb requires a current of 0.5 A to operate correctly. If the lightbulb is connected to a battery for 10 minutes, how many elementary charges pass through the lightbulb?

<p>$1.87 \times 10^{20}$ (D)</p> Signup and view all the answers

What distinguishes the positive and negative poles in the circuit symbol of a battery?

<p>The longer line represents the positive pole, while the shorter line represents the negative pole. (D)</p> Signup and view all the answers

A circuit contains a battery, a resistor, and a switch. The switch is initially open. What happens when the switch is closed?

<p>Current starts to flow through the circuit, and the resistor dissipates electrical energy as heat. (D)</p> Signup and view all the answers

Flashcards

Electric Current (I)

The quantity of charge (q) passing a point in a time interval (Δt). Measured in Amperes (A).

Direct Current (DC)

A flow of electrons in one direction through a circuit.

Amper (A)

Indicates the amount of electric charge passing through a conductor per unit of time.

Electron Flow Direction

Electrons flow from the negative terminal, through conducting wires, toward the positive terminal.

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Current Calculation Formula

I = q / ∆t, calculating current given charge and time.

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Electric Current - Time

When time increases and the quantity of electric charge remains constant the electric current decreases.

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Electric Current - Charge

When the quantity of electric charge increase and time remains constant, the electric current increases

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Electric current through a wire.

To calculate the current (amperes) through a wire, divide the charge (coulombs) that passes through it by the time (seconds)

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Charge (q)

Calculated by multiplying current (I) by the change in time (Δt).

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Energy Conversion (ΔEE)

The energy converted from electrical energy to other forms (like heat or light).

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Conventional Current

The flow of positive charge from the anode to the cathode in a circuit.

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Electron Flow

The flow of negative charge (electrons) from the cathode to the anode in a circuit.

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Voltage (V)

The difference in electrical potential energy between two points in a circuit; drives electric current.

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J.J. Thomson

Scientist who discovered the electron, proving that negative charges were electrons.

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Benjamin Franklin

He thought that excess electricity was positive and a deficit was negative

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Elementary Charge

The magnitude of charge on a single proton or electron; e = 1.602 x 10^-19 C.

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Calculating Charge (q)

q = N * e, where q is the total charge, N is the number of excess protons or electrons, and e is the elementary charge.

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Electric Circuit

A continuous path for electric current to flow.

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Battery in a Circuit

Provides the potential difference (voltage) to drive current.

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Load in a Circuit

Consumes electrical energy, converting it to another form (e.g., light, heat).

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Switch in a Circuit

Allows for controlled opening/closing of a circuit, stopping or starting current flow.

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Open Circuit

A circuit with a break or disconnection, preventing current flow.

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Closed Circuit

A circuit with a complete, unbroken path, allowing current to flow.

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Calculating Number of Electrons

The number of electrons (N) is the total charge (q) divided by the charge of one electron (e).

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What is a Circuit Diagram?

A diagram showing the path of electrical current using symbols to represent components.

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What is an Ammeter?

A device that measures electric current in amperes (A).

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How to connect an ammeter?

Ammeters are connected in series to measure the current flowing through a component.

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Ammeter Definition

An electrical device that measures electric current.

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Ammeter in a Circuit

Connected in series to measure current flow; disconnecting it breaks the circuit.

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Series Circuit

A circuit with one complete path for current.

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Parallel Circuit

A circuit with more than one complete path for current.

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Voltmeter

Measures potential difference (voltage) between two points in a circuit.

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Ammeter

Measures the current flowing through a point in a circuit.

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Voltmeter Placement

Voltmeters are connected across components to measure voltage drop.

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Ammeter Placement

Ammeters are integrated directly into the path to measure current.

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Voltmeter Symbol

A device that measures voltage in a circuit.

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Ammeter Symbol

A device that measures current in a circuit.

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Electrical Resistance

Opposition to the flow of electric current in a conductor.

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Resistance vs. Area

Resistance is inversely proportional to the cross-sectional area of a conductor.

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Resistivity (ρ)

A material property that quantifies how strongly a material opposes the flow of electric current.

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Resistance Formula

R = ρL / A, where R is resistance, ρ is resistivity, L is length, and A is cross-sectional area.

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Calculate Resistance

Calculate the resistance of a conductor given its resistivity, length, and cross-sectional area.

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Cross-Sectional Area

Area = 𝝅r^2

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Resistance Calculation Answer

1.30 Ω

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Resistance vs. Lenght

The longer the object the more resistance

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Study Notes

  • Direct current (DC) flows in one direction through a circuit.
  • Electrons flow from the negative terminal, through conducting wires, to the positive terminal.

Electric Current

  • Electric current (I) is the quantity of charge (q) passing a point in a time interval (Δt).
  • The formula is I = q/Δt
  • The unit of electric current is the ampere (A).
  • 1 A = 1 Coulomb / second
  • Analogy: More water flows through a bigger cross-section at the same water pressure.

Practice Problems

  • Charge (q) = current (I multiplied by time (Δt)
  • Electrical Energy (ΔE) = charge (q) multiplied by voltage (V)
  • 1752: Benjamin Franklin thought excess electricity was positive, a deficit was negative, incorrectly assuming positive charges move.
  • 1800: Alessandro Volta invented the electrochemical cell.
  • 1876: An experiment at Harvard showed negative charges move.
  • J.J. Thomson (1856-1940) discovered the electron.

Electron vs. Current Flow

  • Current (I) is the flow of positive charge (anode to cathode).
  • Electron flow is the flow of negative charge (cathode to anode).

Elementary Charge

  • R. Millikan found the size of one elementary charge: e = 1.602 x 10⁻¹⁹ C.
  • The charge is the magnitude of the charge on a proton (+1 e) or an electron (-1 e).
  • An object with N more protons than electrons has a charge q = N x e.

Electric Circuit

  • A switch can open/close a circuit with a battery, load, and conductor.
  • An open circuit has a break preventing current flow.
  • A closed circuit has complete connections.
  • A battery's longer line is the positive pole; the shorter line is negative.

Measuring Current

  • Electric current is measured in amperes (A) using an ammeter.
  • Small currents are measured in milliamps (mA) using a milliammeter or galvanometer.
  • Ammeters connect in series within a circuit for measuring current flowing through a resistor.
  • A multimeter measures current at one location when set as an ammeter.
  • Ammeter connects in series to measure the current.
  • Ammeter is part of a circuit.

Electric components

  • A circuit can have one complete path (series) or more than one (parallel).
  • Voltmeters connect in parallel; ammeters in series.
  • Ammeters are part of the circuit.

Electric Circuit Elements

  • Switch (open and closed), ammeter, light bulb, conductor crossing (with and without contact), voltmeter, DC generator, cell, motor, AC generator, resistance, battery power supply, ground.

Electrical Resistance

  • Electrical resistance (R) is a property describing how difficult electricity travels through a material.
  • Metal conductors carrying electric current is comparable to a water pipe carrying water current.

Ohm's Law

  • Potential difference across a load equals current multiplied by resistance: V = IR.
  • Resistance measured in ohms (Ω).
  • One ohm allows one ampere of current to move through with one volt applied.
  • Materials not obeying Ohm's law are nonlinear/non-ohmic.
  • Water analogy: bigger cross area = less resistance = easier flow = bigger current
  • Current is proportional with Potential Difference and inversely proportional with resistance.

Power

  • Appliances are rated for power output (P), the rate of transforming electric energy.
  • Examples: Electric range - 12,000 W | Electric clothes dryer - 5,000 W | Light bulb - 4.5 - 15 W
  • Power is work done per unit time or energy transferred per unit time.
  • Proportionality constant is the resistivity.

Resistance Factors

  • For fixed diameter electric conductor, resistance increases proportionately with length.
  • For fixed length conductor, resistance varies inversely with cross-sectional area.

Resistance Equation

R=ρ(L/A)

  • where ρ is resistivity, L is length, A is cross-sectional area.

Calculating Resistance

  • Measured by Ω (ohm).
  • Resistivity with the symbol ρ and measured by Ω⋅m (ohm metres).
  • Length of conductor = L= metres.
  • Cross sectional area= A =metres squared.
  • silver: 1.6 x 10⁻⁸ Ω⋅m
  • copper: 1.7 x 10⁻⁸ Ω⋅m
  • aluminum: 2.7 x 10⁻⁸ Ω⋅m
  • tungsten: 5.6 x 10⁻⁸ Ω⋅m
  • nichrome: 100 x 10⁻⁸ Ω⋅m
  • carbon: 3500 x 10⁻⁸ Ω⋅m
  • germanium: 0.46 Ω⋅m
  • glass: 10¹⁰ to 10¹⁴ Ω⋅m

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