Overview
This lecture covers the key concepts of current electricity, including definitions, formulas, measuring instruments, circuit components, and calculations for both series and parallel circuits.
Types of Electricity
- There are two types of electricity: static electricity (stationary charges) and current electricity (flowing charges).
Current Electricity Basics
- Current electricity deals with charges that flow in conductors.
- Current (I) is defined as the rate of charge flow.
- The unit for current is the ampere (A).
- The unit for charge is the coulomb (C).
- Formula: Current (I) = Charge (Q) / Time (t); Q = I × t.
Measuring Instruments
- An ammeter measures current and is connected in series in a circuit.
- Positive and negative terminals of an ammeter must connect to the respective battery terminals.
- A voltmeter measures voltage and is connected in parallel across a component.
Voltage: Electromotive Force & Potential Difference
- Electromotive Force (EMF) is the energy supplied per coulomb of charge by a cell; unit: volt (V).
- EMF formula: EMF = Energy supplied (E) / Charge (Q).
- Potential difference (PD) is the energy converted per unit charge as it passes through a component; unit: volt (V).
- PD formula: PD = Energy converted / Charge.
Resistance
- Resistance is the opposition to the flow of current; measured in ohms (Ω).
- Formula: Resistance (R) = Voltage (V) / Current (I).
- A resistor is any component that provides resistance in a circuit.
Example Calculations
- Use formulas to solve for current, charge, voltage, and resistance when given appropriate values.
- Always identify known and unknown values before substituting into formulas.
Circuit Components & Symbols
- Common symbols: resistor (zig-zag line), variable resistor (arrow across resistor), ammeter (circle with A), voltmeter (circle with V), light bulb, battery/cell, galvanometer.
Series and Parallel Circuits
Series Connection
- Components are on the same path; resistors add up: R_total = R1 + R2 + ...
- Voltage is shared/different across components; current is the same throughout.
Parallel Connection
- Components are on separate paths; reciprocals of resistors add: 1/R_total = 1/R1 + 1/R2 + ...
- Voltage is the same across all branches; current is different/shared between branches.
Application to Exam Questions
- Identify circuit type (series or parallel) to use appropriate formulas for resistance, voltage, and current.
- For series: add resistances; for parallel: use reciprocal formula.
- Example questions involve calculating total resistance, potential difference, and current in both series and parallel circuits.
Key Terms & Definitions
- Current (I) — The rate of flow of charge (unit: ampere, A).
- Charge (Q) — The quantity of electricity (unit: coulomb, C).
- Voltage (V) — The energy per unit charge (unit: volt, V).
- Electromotive Force (EMF) — Energy supplied per coulomb from a source.
- Potential Difference (PD) — Energy converted per coulomb across a component.
- Resistance (R) — Opposition to current flow (unit: ohm, Ω).
- Resistor — A component providing resistance in a circuit.
- Ammeter — Device to measure current, connected in series.
- Voltmeter — Device to measure voltage, connected in parallel.
Action Items / Next Steps
- Review and memorize all definitions, formulas, and units.
- Practice solving circuit problems involving current, voltage, resistance, and identifying circuit types.
- Study electrical component symbols and understand how to draw simple circuit diagrams.