Circuits: Resistance and Switches

• Resistance limits electric current flow in a circuit.
• Resistance is measured in Ohms (Ω).
• Resistance converts electrical energy into heat, as seen in light bulbs and heaters.

Types of Resistors

• Carbon resistors: Used in small electronics.
• Wire wound resistors: Used in high power applications
• Filament in light bulbs acts as a resistor, producing heat and light.

Switches

• Switches control electrical flow by opening (OFF) or closing (ON) the circuit path.

Switch Types

• Toggle Switch: Commonly used as light switches in homes.
• Push-button switch: Found in doorbells and keyboards.
• Rocker switch: Used in appliances.
• Example: A wall switch breaks the circuit to turn off a light.

Variable Resistors

• Variable resistors change resistance to control electrical flow in a circuit.

Variable Resistor Types

• Rheostat: Adjusts current, like dimmer switches or motor speed controls.
• Potentiometer: Controls voltage, as seen in volume knobs or guitar tone controls.
• Example: A dimmer switch reduces current to make a light bulb glow dimly.

Ammeter

• Ammeter: Measures electrical current flowing through a circuit.

Usage

• Connected in series with the component to measure current.
• Measures current in Amperes (A).
• Has low resistance to allow current to flow freely.
• Helps determine if a circuit is functioning properly.

Potential Difference

• Formula: V = I x R (Voltage = Current x Resistance).

Superconductors

• Superconductors have zero electrical resistance below a critical temperature, allowing electricity to flow without energy loss.

Superconductor Properties

• No electrical resistance and no energy loss as heat.
• Can create powerful magnetic fields.

Superconductor Uses

• Used in MRI machines and particle accelerators.
• Require very low temperatures (near absolute zero) to function using coolants like liquid helium or nitrogen.

Superconductor Examples

• Niobium-titanium (NbTi).
• Yttrium barium copper oxide (YBCO).

Conductors

• Conductors allow electricity to flow easily due to free-moving electrons.

Conductor Properties

• Low resistance resulting in high conductivity

Conductor Uses

• Used in wiring, circuits, and power transmission.

Conductor Examples

• Metals like copper, silver, gold, and aluminum.
• Graphite (a non-metal conductor).
• Silver is the best conductor in nature, but copper is more cost-effective.

Insulators

• Insulators do not allow electricity to flow easily because their electrons are tightly bound to their atoms.

Insulator Properties

• High resistance and poor conductivity.
• Prevents electrical shocks and short circuits.

Insulator Examples

• Rubber (used in power cords).
• Glass (used in high-voltage insulators).
• Plastic, wood, and ceramic.

Electrolyte

• Electrolyte: A substance that contains free ions and conducts electricity.

Electrode

• Electrode: A conductive material where oxidation and reduction occur.

Dry Cell

• Dry Cell: An electrochemical cell with a paste-like electrolyte in order to prevent leakage.

Primary Cell

• Primary Cell: Non-rechargeable

Electrochemical Cell

• Electrochemical Cell: A device that converts chemical energy into electrical energy.

Current Calculation

• Formula: Current = Charge / Time

Circuit Breakers

• Circuit Breakers: A switch that automatically turns off power if too much current flows.
• Circuit breakers can be reset instead of replaced, unlike fuses.
• They protect homes and buildings from electrical overloads.

Batteries

• Batteries: A collection of two or more electrochemical cells connected together to produce a higher voltage.
• Example: A 9V battery contains multiple smaller cells connected in series.

Series vs Parallel

• Series connections increase voltage.
• Parallel connections increase battery life.

Electrochemistry

• Electrochemistry: The study of chemical reactions involving electron transfer, creating electrical energy.

Electrochemical Applications

• Batteries and fuel cells.
• Corrosion prevention.
• Metal plating and purification.

Electrolysis

• Electrolysis: Using electricity to drive a non-spontaneous chemical reaction.
• Example: Electrolysis of Water splits water (H2O) into hydrogen (H2) and oxygen (O2) using electricity.

Electrolysis Electrodes

• Anode (+): Oxygen is produced.
• Cathode (-): Hydrogen is produced.

Electrolysis Uses

• Production of hydrogen fuel.
• Purification of metals (e.g., refining aluminum from ore).
• Electroplating.

Electroplating

• Electroplating: Coating a metal object with a thin layer of another metal using electrolysis.

How it Works

• The object to be coated (cathode) is placed in a solution containing metal ions.
• A metal electrode (anode) supplies the coating material.
• Electricity is applied, causing metal ions to deposit onto the object.

Electroplating Uses

• Jewelry (gold/silver plating).
• Protecting metals from rust (chrome plating).
• Improving the appearance and durability of objects.

Lightning

• Lightning: A sudden discharge of electricity between clouds or the ground.
• It is dangerous due to its high voltage and energy.

Lightning Dangers

• Can cause fires in buildings, forests, and grasslands.
• Can injure or kill people and animals due to electric shock.
• Can damage power lines and electrical equipment.
• Can cause electrocution if someone is in contact with water/metal.

Electrochemical Cell Components

• A substance (usually liquid/paste) that contains free ions and conducts electricity.

Electrochemical Cell Electrodes

• Conductive materials (usually metals) that allow electrons to enter or leave the cell.
• Anode (-): Where oxidation (loss of electrons) occurs.
• Cathode (+): Where reduction (gain of electrons) occurs.
• Ion Flow: The movement of ions within the electrolyte balances the charge as electrons move through an external circuit.

Dry Cell

• Dry Cell: An electrochemical cell with a paste electrolyte to prevent leakage.

Dry Cell Components

• Electrolyte: A paste that allows ion movement.

Dry Cell Electrodes

• Anode (-): Zinc casing (undergoes oxidation).
• Cathode (+): Carbon (graphite) rod in a manganese dioxide mixture (reduction).
• Ion Flow: Zinc releases electrons, while manganese dioxide gains electrons.

Wet Cells

• Wet Cells: Use a liquid electrolyte, enabling continuous reactions.

Wet cells Components

• Electrolyte: Sulfuric acid solution (in lead-acid batteries).

Wet Cell Electrodes

• Anode (-): Lead plate.
• Cathode (+): Lead dioxide plate.
• Ion Flow: Chemical reactions between lead and sulfuric acid generate electrons.

Rechargeable Cells

• Rechargeable Cells: Can be recharged and reused by reversing the chemical reaction using external electricity.

Rechargeable Cell Types

• Primary cells: Non-rechargeable, designed for single use, example: Alkaline Batteries.
• Secondary cells: Rechargeable, designed for multiple uses, example: Lithium Batteries, Lead-acid car batteries.