Physics Chapter 22: Electric Current Basics

Study Notes

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.