Physics Chapter 22: Electric Current Basics

Chapter 22: Electric Current - Section 1: Current and Circuits

• Essential Questions:

  • What is electric current?
  • How does energy change in electric circuits?
  • What is Ohm's law?
  • How are power, current, potential difference, and resistance related mathematically?

• Vocabulary:

  • electric current
  • conventional current
  • battery
  • electric circuit
  • ampere
  • resistance
  • resistor
  • parallel connection
  • series connection

• Objectives:

  • Define electric current.
  • Distinguish between conventional and electron current.
  • Calculate electric current using the formula.
  • Define resistance.
  • Describe the relationship between voltage (V) and current (I) using Ohm's law.
  • Apply Ohm's law to solve problems.
  • List factors affecting resistance.
  • Define electrical power and derive the relationship between power (P), current (I), and voltage (V).

• Potential Difference and Flow of Charges:

  • A battery creates a potential difference, allowing charge flow.
  • Conventional current flows from positive to negative.
  • Electrons flow from negative to positive.
  • The flow of charged particles is electric current.

• Energy Transformation:

  • Electric charges leave with high electrical energy.
  • Energy is transferred to a device (e.g., lightbulb, motor).
  • Input energy changes forms (e.g., light, heat, kinetic).
  • Charges return to the battery with low electrical energy.
  • A battery is like a pump, maintaining potential difference.

• Electric Current:

  • Electric current is the rate of flow of electric charges, or the quantity of charge passing each second.
  • Formula: Current (I) = Charge (q) / Time (t)
  • Units: Coulombs (C) for charge and amperes (A) for current.

• Direction of Electric Current:

  • Conventional current is the direction a positive charge would move (positive terminal to negative).
  • Electron current is the direction of electron flow (negative terminal to positive).

• Practice Problems (Examples):

  • Problem 1: Calculate current given charge and time.
  • Problem 2: Calculate charge given current and time.
  • Problem 3: Calculate current given number of electrons and time.
  • Problem 4: Calculate number of electrons given current and time.

• Electric Circuit:

  • A closed loop for charge flow is an electric circuit.
  • Circuits are represented with symbols.

• Common Circuit Symbols:

  • Shows various circuit components, including: conductor, switch, fuse, capacitor, ground, battery, resistor, potentiometer, lamp, DC generator, voltmeter, ammeter.

• Parallel and Series Connections:

  • A series circuit has a single path for current. Current is the same in all elements.
  • A parallel circuit has more than one path for current. Potential difference is the same across all branches.

• Instruments Used to Measure Voltage and Current:

  • Voltmeter: Measures potential difference (connected in parallel).
  • Ammeter: Measures current (connected in series).
  • Multimeter: Combines voltmeter and ammeter functions.

• Voltmeter and Ammeter Connection:

  • Ammeter connects within the circuit (in series).
  • Voltmeter connects across the circuit (in parallel).

• Practice Problem (Example):

  • Draw a circuit diagram, including components.

• Resistance and Ohm's Law:

  • Resistance: Opposition to current flow in a material.
  • Ohm's Law: Current (I) is directly proportional to voltage (V) and inversely proportional to resistance (R). (V=IR)
  • Units: Volts (V) for voltage, amperes (A) for current, ohms (Ω) for resistance.

• Ohm's Law Mathematical Formula:

  • Showing the triangle to represent the formula, and how to rearrange the formula to compute V, I or R

• Resistors:

  • Fixed resistors: Have constant resistance.
  • Variable resistors (e.g., potentiometer, rheostat): Resistance can be changed.

• Factors Affecting Resistance:

  • Length: Resistance increase with length
  • Cross-sectional area: Resistance decreases with the increase of cross sectional area.
  • Temperature: Resistance increases with the increase of temperature.
  • Material: Resistance varies with the material used.

• Power:

  • Power is the rate at which energy is transferred or converted.
  • Formula: Power (P)= Energy (E) / Time (t)
  • Units: Watts (W) for power, Joules (J) for energy, and seconds (s) for time.

• Electrical Power:

  • Explaining the relationship between energy, charge, voltage, and current.
  • Relating power, current and voltage.(P=IV)

• Example Problems (Power and Energy):

• Practice problems and example problems on circuits calculating energy, power, current, voltage, and resistance within example problems.

• Section 1 Review Questions:

  • Summary of the section and review questions.

Explore the fundamental concepts of electric current in Chapter 22. This quiz covers essential questions about electric circuits, Ohm's law, and the relationships between current, voltage, and resistance. Test your understanding of key vocabulary and objectives related to electric current.