Thermodynamics Exam Cheat Sheet: Problem-Solving Recipes

🔹 Problem 1: Property Changes & T-s Sketch

(HW 9 Q1–Q3)
1a. Ideal-Gas Entropy Change

Statement: Air (ideal gas) in a piston-cylinder goes from State 1: T₁ = 350 K, p₁ = 100 kPa to State 2: T₂ = 550 K, p₂ = 700 kPa. Find Δs (kJ/kg·K) (a) reversible, (b) with irreversibilities.

1b. Isothermal Water Compression

Statement: 1 kg water in a piston-cylinder, initially saturated vapor at T = 160 °C, p = 150 kPa, isothermally compressed to saturated liquid. Work on water W = -471.5 kJ. Find (a) Q (kJ), (b) ΔS (kJ/K). Sketch T-s.

Steps for 1a (Ideal Gas)

1. Formula:

   

2. Compute

   • 

3. Evaluate

   

4. Irreversible:

   

Steps for 1b (Water Compression)

1. 1st Law:

   

2. Table Lookup at 160 °C (saturated):

   • 

3. Compute ΔU:

   

4. Compute

Mamíferos: Las hembras tienen mamas que producen leche para alimentar a las crías, el cuerpo está cubierto por pelos. La función principal es proteger del frio al animal.
Pelaje: raíz dentro del funículo piloso .Los pelos nuevos sacan los pelos viejos. La glándula sebácea lo hace más flexible el pelo. Lana (largo y fino), cerda (áspero y grueso), vello (suave y corto) y púa (largo y puntiagudo)
La temperatura: Es constante. Si sube o baja la temperatura siempre se mantiene constante.
Hibernación: desciende -10 Cº / Duerme no come y se esconde.
Invernación: baja la temperatura pero un duerme profundamente, come y hace algunas actividades.
La fecundación interna se produce en el ovulo con el esperma.
Sistema digestivo: Boca -faringe-

A/C/B/D/A/B/B/B/B/C/A/B/A/D/A/C/C/C/A/B/D/A/A/B/B/A/C/D/B/D

1. Stopwatch Accuracy

a) Stopwatch

b) To have more accuracy

c) i) 3rd

ii) (3.93 + 4.07 + 3.99) / 3 = 11.99 / 3 = 4

iii) 4 / 10 = 0.40

2. Water Speed Measurement

a) First, measure the distance between bridge X and bridge Y. Then, place the stick in the water at bridge X and time how long it takes to reach bridge Y. Calculate the speed by dividing the distance by the time. Repeat this process at least three times. Add all the results together and divide by three to get the average speed.

b) 2nd box

3. Acceleration and Force

a) i) 24 / 60 = 0.4 m/s²

ii) 7.5 × 10⁵ × 0.4 = 300,000 N

b) Speeding up / Slowing down / Steady speed / At rest

4. Resultant Force and Density

a) i) 280 - 250 = 30 N

ii) Up

b)... Continue reading "Physics Exam Answers and Explanations" »

Energy: Units and Types

• Unit of energy: Joule (J)
• Conservation of Energy: Energy cannot be created or destroyed, only transferred or transformed.
• Kinetic Energy: Energy of motion.
• Potential Energy: Stored due to position (e.g., at the top of a pendulum).

Conduction

• Occurs mainly in solids.
• Particles transfer energy by vibrating and passing it to neighbors.
• Metals are good conductors.
• Poor conductors (insulators), e.g., air and layers of clothing.

Convection

• Happens only in fluids (liquids and gases).
• Heated fluid becomes less dense → rises.
• Cooler fluid becomes more dense → sinks.
• Creates convection currents.
• Example: Hot water in a pan rises to the top.

Radiation

• Transfer by infra-red waves.
• Only method that works in a vacuum (space).
• Best absorber/emitter:

Core Thermodynamic Principles

• Calorimetry: Measures heat transfer in a process.
• Absolute Zero: Lowest temperature; no molecular motion (0 K).
• Clausius Statement: Heat does not flow from cold to hot by itself.
• Enthalpy: Total heat content (H = U + PV).
• Entropy: Measure of disorder; increases in natural processes.
• Diffusion: Particles move from high to low concentration.
• Efficiency: Useful output divided by energy input.
• Gibbs Free Energy: Energy available to do work (G = H - TS).
• Internal Energy: Energy stored inside a system.
• Heat Capacity: Heat needed to raise an object's temperature by 1°C.
• Latent Heat: Heat for phase change without temperature change.
• Quasistatic Process: Very slow, system stays in equilibrium.
• Reversible Process: Can go backward with

Chapter 29: The Magnetic Field

Magnetic Poles and Materials: Like poles repel (+ +), opposite poles attract (+ -). Paramagnetic materials are magnetized only in the presence of a strong external magnetic field. Magnetic flux flows from north to south.

Gauss's Law for Magnetism

The magnetic flux through any closed surface is always zero. There is no way to isolate a north or south magnetic pole (no magnetic monopoles).

The most elementary electric field is from a point charge (a static charge), while the most elementary magnetic flux density is from a magnetic dipole (a small magnet or magnetic bar).

The induced magnetic dipole always has an opposite pole facing the solenoid.

Solenoid:

An electric charge experiences a magnetic force in a magnetic field,... Continue reading "Physics Formulas and Concepts: Magnetism, Induction, and Optics" »

1. Ohm’s Law (V–I Relationship)

Aim

To verify Ohm’s Law and determine the resistance of a metallic conductor.

Apparatus

Battery, ammeter, voltmeter, rheostat, key, and resistance wire.

Theory

Ohm’s Law states that at a constant temperature, the current is directly proportional to the potential difference: V = IR.

Procedure

• Connect the circuit (ammeter in series, voltmeter in parallel).
• Adjust the current using the rheostat.
• Record the V and I readings.
• Plot a graph of V versus I.

Observation

A straight-line graph passing through the origin.

Result

Ohm’s Law is verified. Resistance R = V/I (slope of the graph).

2. Parallel Combination of Resistances

Aim

To verify the law of parallel combination using a meter bridge.

Theory

1/Rp = 1/R1 + 1/R2

Result

The... Continue reading "Physics Lab Experiments and Activities Manual" »

Physical Quantities and Measurement

A physical quantity is a property of a body or phenomenon that can be measured and expressed by a number and a unit (e.g., 5 m, 10 s, 3 kg). It allows us to describe physical laws quantitatively. A physical quantity is defined either by specifying how it is measured or by stating how it is calculated from other measurable quantities.

Key Measurement Concepts

• Unit of measurement: A standard reference used for comparing quantities of the same kind (e.g., meter for length, second for time).
• Direct measurement: The quantity is measured directly using an instrument (e.g., measuring length with a ruler).
• Indirect measurement: The quantity is obtained from other measurements using a mathematical relationship (e.g., calculating

1. SONAR (Sound Navigation and Ranging)

SONAR is a system used to determine the presence of submerged submarines or enemy aircraft. It utilizes the properties of ultrasonic waves to identify the depth of the sea and detect obstacles.

• Mechanism: The SONAR transmitter emits ultrasonic rays in various directions. When these rays strike an obstacle, they reflect back to the receiver. By measuring the distance and time of the transmitted and reflected waves, the velocity of the ultrasonic wave is calculated.
• Mathematical Calculation: If the distance traveled by the transmitted and reflected wave is AC + BC, and velocity v = (AC + BC) / t, then v = 2CO / t. Therefore, the depth of the sea is CO = vt / 2.

2. Piezoelectric Method

Piezoelectric Effect

When... Continue reading "Ultrasonic Wave Generation and Superconductor Properties" »

Chapter 7: Generating Electricity

DC motors convert electrical energy into kinetic energy. Magnetic flux is the amount of magnetic field flowing through a given area, determined by the density of field lines and the surface area. Two factors affect magnetic flux: 1. Area and 2. Magnetic field strength.

Faraday's law states that a changing magnetic flux in a conducting loop or coil induces an electromotive force (EMF) with a magnitude proportional to the rate of change of magnetic flux. Electromagnetic induction occurs when the magnetic flux through a loop changes over time, creating a potential difference. This induces a current in the loop.

The EMF graph is negative when the magnetic flux graph has a positive gradient, and vice versa. Lenz's