Thermal Energy and Radioactivity Lecture Flashcards

Temperature Scales and Measurements

• Fahrenheit Scale     * Body Temperature: $100^{\circ}F$     * Boiling Point of water: $212^{\circ}F$     * Freezing point of water: $0^{\circ}F$     * Freezing point of salt water: $32^{\circ}F$

• Celsius Scale     * Based on the freezing and boiling points of water.     * Boiling point of water: $100^{\circ}C$     * Freezing point of water: $0^{\circ}C$

• Kelvin Scale     * Directly proportional to the average kinetic energy of the particles.     * Boiling Point of water: $373\,K$     * Freezing Point of water: $273\,K$     * Absolute Zero ($0\,K$):         * This is the theoretical point where molecules stop moving completely.         * It is considered "not possible" because the object would effectively disappear if all molecular movement ceased.     * Conversion Formula: $^{\circ}C + 273 = K$

Fundamental Concepts of Thermodynamics

• Thermal Energy: This is the total amount of energy contained in a sample of a substance due to the movement of its particles.

• Heat: Defined as the transfer of thermal energy from one object or system to another.

• Temperature: A measure of how fast molecules are moving, defined specifically as the average kinetic energy of the particles.

• Thermal Equilibrium: The state achieved when all particles in a system reach the same temperature and energy exchange ceases.

• Newton's Law of Cooling: States that the rate of cooling of an object depends directly on the temperature difference between the object and its surroundings.

Methods of Heat Transfer

• Conduction     * The transfer of energy through a solid or between two substances in direct physical contact.     * Mechanism: Particles bumping into each other to pass along energy.     * Conductors: Materials that transfer heat well (e.g., metals). In metals, this is largely due to the presence of free electrons.     * Insulators: Materials that resist heat transfer. They often contain spaces, such as those found in a thermos.     * The Thermos Design: Utilizes a vacuum and mirrors inside to prevent heat loss through conduction and radiation.

• Convection     * The transfer of energy through a fluid (liquid or gas).     * Mechanism: Driven by density differences.         * Increase in temperature: The fluid expands, and its density decreases (it rises).         * Decrease in temperature: The fluid contracts, and its density increases (it sinks).

• Radiation     * The transfer of energy through a vacuum.     * Mechanism: Energy is transferred via electromagnetic (EM) waves.     * Examples: Energy arriving from the Sun.     * Emission: All matter emits radiation.     * Frequency Relationship: Frequency ($f$) is proportional to the temperature in Kelvin ($K$), denoted as $f \sim T$.

• Greenhouse Effect: The process by which certain gases trap heat in the atmosphere.

States of Matter

• Solid     * The lowest energy state.     * Particles are packed very close together.

• Liquid     * Contains more energy than the solid state.     * Takes the shape of its container.     * Possesses a definite volume.

• Gas     * Contains more energy than the liquid state.     * Has no definite shape or volume.     * Particles move very quickly and are spread far apart.

• Plasma     * A gas composed of positive ions and electrons at a very high temperature.     * Examples: Northern Lights (Aurora Borealis) and fluorescent lights.

Phase Changes and Energy Dynamics

• Energy and Temperature Rules     * When energy is added to a system, either the temperature changes or the phase changes, but typically not both at once.     * Temperature remains constant while a phase is actively changing.

• Specific Phase Transitions     * Sublimation: The direct transition from a solid to a gas.     * Evaporation: Transition from a liquid to a gas; this process requires an input of energy.     * Condensation: Transition from a gas to a liquid.     * Freezing: Transition from a liquid to a solid.

• Thermic Processes     * Endothermic: Heat is pulled into the system from the surroundings (e.g., an ice pack).     * Exothermic: Heat is pushed out of the system into the surroundings (e.g., a hand warmer).

Quantitative Thermal Physics

• Equations     * For temperature changes: $Q = m c \Delta T$         * $Q$: Heat (Energy)         * $m$: Mass         * $c$: Specific heat capacity         * $\Delta T$: Change in temperature     * For phase changes: $Q = m L$         * $L$: Latent heat

• Specific Heat Capacity ($c$)     * The amount of heat energy required to raise the temperature of $1\,g$ of a substance by $1^{\circ}C$.     * Water Specific Heat: Approximately $4184\,J/kg \cdot ^{\circ}C$ ($4.184\,J/g \cdot ^{\circ}C$).     * Calorie Conversions:         * $1000\,c = 1\,kcal = 1\,C$ (Food Calories).         * $1\,calorie = 4.184\,Joules$.     * Energy Requirements: A substance with a lower specific heat requires less energy to change temperature; a substance with a higher specific heat requires more energy.

Laws of Thermodynamics and Expansion

• First Law: The gain or loss of thermal energy depends on the heat entering or leaving a system.

• Second Law: Heat moves spontaneously from areas of high temperature to areas of low temperature.

• Third Law: No system can reach absolute zero, although systems can come very close.

• Thermal Expansion and Contraction     * Temperature Increase ($T \uparrow$) $\rightarrow$ Particle Speed Increase $\rightarrow$ Substance Expands.     * Temperature Decrease ($T \downarrow$) $\rightarrow$ Particle Speed Decrease $\rightarrow$ Substance Contracts.     * Water Anomaly: Water expands when it freezes, which causes it to become less dense than liquid water.

Nuclear Physics and Radioactivity

• The Nucleus     * Extremely tiny compared to the atom.     * Contains Protons and Neutrons.     * Electrical forces (between protons) tend to push the nucleus apart.     * The Strong Nuclear Force holds the protons and neutrons together; it only acts over very short distances.

• Types of Radiation/Particles     * Alpha Particle ($\alpha$): A Helium nucleus ($He$) consisting of 2 protons and 2 neutrons. It has a $+2$ charge. It can be stopped by a single sheet of paper.     * Beta Particle ($\beta$): A high-speed electron ($e^-$) emitted from the nucleus. It can be stopped by metal foil.     * Gamma Radiation ($\gamma$): A high-energy electromagnetic (EM) wave. It has no charge and can pass through paper and metal, usually requiring lead to be stopped.

• Atomic Terms and Notation     * Isotopes: Atoms with the same number of protons but a different number of neutrons.     * Ions: Atoms that have lost or gained electrons.     * Standard Notation: $^{235}_{92}U$         * The top number (Mass Number) is the sum of protons and neutrons ($A$).         * The bottom number (Atomic Number) is the number of protons ($Z$).         * Number of neutrons = Mass Number ($A$) - Atomic Number ($Z$).     * Photoelectric Effect: The ejection of electrons from a material when light/energy hits it.

Questions & Discussion

• Q: Why doesn't the temperature of boiling water increase from $100^{\circ}C$?     * A: Because the water is going through a phase change; during a phase change, the temperature remains constant as energy is used to break molecular bonds rather than increase kinetic energy.

• Q: Distinguish between an ion and an isotope.     * A: Ions are formed when an atom has lost or gained electrons; isotopes are atoms of the same element that have different numbers of neutrons.

• Q: Which isotope has the greater number of neutrons, $U-235$ or $U-238$?     * A: $U-238$ because it has a higher mass number.

• Q: When an atom undergoes radioactive decay, why does it become a completely different element?     * A: Because the number of protons in the nucleus is changed, and the atomic number (number of protons) determines the identity of the element.

• Decay Scenarios     * U-238 Alpha Decay: It becomes Thorium-234.     * Thorium-234 Alpha Decay: It becomes Radium-230.     * Thorium-234 Beta Decay: It becomes Protactinium-234.