Physics Midterm Exam 2025 PDF

PHYSIC MIDTERM EXAM 2025 1.ATOMIC STRUCTURE What an Atom Is: ​ Smallest particle that maintains element's properties ​ Made of protons, neutrons, electrons ​ Has central nucleus with electrons orbiting Properties of Subatomic Particles: 1.​ Protons ○​ Charge: +1 ○...

PHYSIC MIDTERM EXAM 2025 1.ATOMIC STRUCTURE What an Atom Is: ​ Smallest particle that maintains element's properties ​ Made of protons, neutrons, electrons ​ Has central nucleus with electrons orbiting Properties of Subatomic Particles: 1.​ Protons ○​ Charge: +1 ○​ Mass: 1 ○​ Location: Nucleus ○​ Determines element (atomic number) 2.​ Neutrons ○​ Charge: 0 ○​ Mass: 1 ○​ Location: Nucleus ○​ With protons, determines mass number 3.​ Electrons ○​ Charge: -1 ○​ Mass: Almost zero ○​ Location: Orbits ○​ Determines chemical properties Atomic and Mass Numbers: ​ Atomic number = number of protons ​ Mass number = protons + neutrons ​ Isotopes = same element, different neutrons Gold-foil Experiment: What happened: ​ Most alpha particles passed straight through ​ Some deflected at large angles ​ Very few bounced back What it meant: ​ Atom mostly empty space  PHYSIC MIDTERM EXAM 2025 ​ Mass/charge concentrated in nucleus ​ Nucleus very small compared to atom ​ Nucleus contains positive charge Why Understanding Atomic Structure Matters When we understand atomic structure, we can explain almost everything about how matter behaves. For example: ​ Why some elements are reactive while others are inert ​ How nuclear power plants generate energy ​ Why certain materials conduct electricity while others don't ​ How radioactive decay occurs The Three Fundamental Particles (MUST UNDERSTAND IN DETAIL) 1. Protons: The Positive Players Protons are like the anchors of atomic identity. Imagine them as the ID cards of atoms - the number of protons (atomic number) determines what element an atom is. For example: ​ 1 proton = Hydrogen ​ 6 protons = Carbon ​ 79 protons = Gold The positive charge of protons serves two crucial functions: 1.​ It attracts electrons, creating the electronic structure that determines chemical properties 2.​ It contributes to nuclear stability through the strong nuclear force Key Properties (MEMORIZE): ​ Mass: 1.67262 × 10⁻²⁷ kg ​ Charge: +1.6 × 10⁻¹⁹ coulombs ​ Location: Always in nucleus ​ Cannot be removed by chemical means 2. Neutrons: The Nuclear Glue Neutrons are the unsung heroes of atomic stability. While they don't have a charge, they're crucial for several reasons: 1.​ Nuclear Stability: ○​ They act as "spacers" between protons ○​ They prevent proton-proton repulsion from tearing the nucleus apart ○​ They contribute to nuclear binding energy  PHYSIC MIDTERM EXAM 2025 2.​ Isotope Formation: ○​ Different numbers of neutrons create isotopes ○​ Example: Carbon-12 has 6 neutrons, Carbon-14 has 8 neutrons ○​ This affects radioactive properties and nuclear stability Key Properties (MEMORIZE): ​ Mass: 1.67493 × 10⁻²⁷ kg ​ Charge: 0 ​ Location: Nucleus only ​ Key to nuclear stability 3. Electrons: The Chemical Actors Electrons are the particles that make chemistry possible. They're like the social butterflies of the atomic world, involved in: 1.​ Chemical Bonding: ○​ Share or transfer between atoms ○​ Create ionic or covalent bonds ○​ Determine molecular structure 2.​ Electrical Conductivity: ○​ Free electrons allow current flow ○​ Different energy levels create band structure ○​ Explain conductor vs. insulator behavior Key Properties (MEMORIZE): ​ Mass: 9.10938 × 10⁻³¹ kg ​ Charge: -1.6 × 10⁻¹⁹ coulombs ​ Location: Energy levels around nucleus ​ Can be gained or lost in chemical reactions Understanding Atomic Mass and Number This is crucial for calculations and understanding nuclear reactions: 1.​ Atomic Number (Z): Number of protons = Number of electrons (in neutral atom) Example: Gold (Au) has 79 protons, so Z = 79 This NEVER changes for an element 2.​ Mass Number (A): Number of protons + neutrons Example: Gold-197 has A = 197 This can vary (isotopes) 3.​ Neutron Number (N): N = A - Z Example: Gold-197 has N = 197 - 79 = 118 neutrons Properties of Subatomic Particles (MUST MEMORIZE ALL VALUES) ​ Protons (MEMORIZE ALL)  PHYSIC MIDTERM EXAM 2025 ○​ Charge: +1.6 × 10⁻¹⁹ coulombs (exactly +1 unit charge) ○​ Mass: 1.67262 × 10⁻²⁷ kg (1.007276 amu) ○​ Location: Nucleus only ○​ Cannot be removed from nucleus by chemical means ○​ Number defines element (atomic number) ○​ Discovered by Rutherford in 1919 ​ Neutrons (MEMORIZE ALL) ○​ Charge: 0 (completely neutral) ○​ Mass: 1.67493 × 10⁻²⁷ kg (1.008665 amu) ○​ Location: Nucleus only ○​ Stabilizes nucleus ○​ With protons, determines isotope (mass number) ○​ Discovered by Chadwick in 1932 ​ Electrons (MEMORIZE ALL) ○​ Charge: -1.6 × 10⁻¹⁹ coulombs (exactly -1 unit charge) ○​ Mass: 9.10938 × 10⁻³¹ kg (1/1836 of proton) ○​ Location: Shells/orbitals around nucleus ○​ Can be gained or lost (ionization) ○​ Determines chemical behavior ○​ Discovered by Thomson in 1897 Critical Atomic Calculations (MEMORIZE) 1.​ Atomic Number (Z) ○​ Number of protons ○​ Number of electrons (in neutral atom) ○​ Example: Gold (Au) = 79 protons 2.​ Mass Number (A) ○​ Number of protons + neutrons ○​ Example: Gold-197 = 79p + 118n = 197 3.​ Number of Neutrons ○​ Mass number - Atomic number ○​ Example: Gold-197: 197 - 79 = 118 neutrons Key Concepts ​ Atomic Number: Number of protons ​ Mass Number: Number of protons + neutrons ​ Isotopes: Same element (same number of protons) but different number of neutrons Gold-foil Experiment (Rutherford) ​ Setup: Alpha particles fired at thin gold foil ​ Observations:  PHYSIC MIDTERM EXAM 2025 ○​ Most particles passed straight through ○​ Some deflected at large angles ○​ Very few bounced back ​ Conclusions: ○​ Atom mostly empty space ○​ Mass concentrated in small, dense nucleus ○​ Nucleus positively charged ○​ Led to nuclear model of atom 2. Types of Radiation Radiation Types (ESSENTIAL KNOWLEDGE) Alpha (α) Radiation (MEMORIZE ALL) ​ Composition: 1.​ 2 protons + 2 neutrons (helium nucleus) 2.​ Written as: ⁴₂He²⁺ or α 3.​ Mass number: 4 4.​ Atomic number: 2 ​ Properties (ALL MUST BE MEMORIZED): 1.​ Charge: ​ +2 (double positive) ​ Most positively charged radiation type ​ Strongly affected by electric fields 2.​ Ionizing Power: ​ Highest ionizing ability ​ Creates ~100,000 ion pairs per cm in air ​ Reason: Large mass and charge ​ Most dangerous if ingested 3.​ Penetrating Power: ​ Lowest penetration of all radiation types ​ Stopped by: ​ Paper (few sheets) ​ Skin layer ​ Few centimeters of air ​ Range in air: 2-10 cm typically 4.​ Magnetic Field Behavior: ​ Strongly deflected ​ Curves toward negative plate ​ Deflection less than beta due to larger mass ​ Path: Circular arc 5.​ Speed: ​ Slowest of all radiation types  PHYSIC MIDTERM EXAM 2025 ​ Typically 15,000 km/s ​ ~5-7% speed of light 6.​ Applications: ​ Smoke detectors ​ Cancer therapy (targeted) ​ Material analysis Beta (β) Radiation ​ Composition: High-speed electrons ​ Charge: -1 ​ Properties: ○​ Moderately ionizing ○​ More penetrating than alpha (stopped by aluminum) ○​ Deflected by magnetic fields (opposite to alpha) ○​ Range in air: meters Gamma (γ) Radiation ​ Composition: Electromagnetic waves ​ Charge: 0 ​ Properties: ○​ Weakly ionizing ○​ Most penetrating (requires lead/concrete) ○​ Not deflected by magnetic fields ○​ Range in air: many meters Half-life ​ Time taken for half of radioactive sample to decay ​ Independent of initial amount ​ Constant for each isotope ​ Calculation: Count rate reduces to half original value 3. Waves Types of Waves ​ Transverse Waves ○​ Vibration perpendicular to direction of travel ○​ Examples: Light waves, water waves, electromagnetic waves ​ Longitudinal Waves ○​ Vibration parallel to direction of travel ○​ Examples: Sound waves, compression springs  PHYSIC MIDTERM EXAM 2025 Wave Anatomy (ESSENTIAL CONCEPTS) Wave Components (MEMORIZE ALL DEFINITIONS) ​ Wavelength (λ) ○​ Definition: Distance between two consecutive crests or troughs ○​ Measurement: Measured in meters (m) ○​ Key point: One complete wave cycle ○​ Example: Light wavelengths typically measured in nanometers ○​ How to identify: Look for repeating pattern in wave ​ Amplitude ○​ Definition: Maximum displacement from equilibrium position ○​ Measurement: Measured from equilibrium to peak (not peak-to-peak) ○​ Physical meaning: Represents wave energy ○​ In sound: Determines loudness ○​ In light: Determines brightness ○​ Key point: Can vary while wavelength stays constant ​ Frequency (f) ○​ Definition: Number of complete waves passing a point per second ○​ Units: Hertz (Hz) = waves per second ○​ Relationship: Higher frequency = shorter wavelength ○​ Example: Human hearing range 20 Hz - 20,000 Hz ○​ Key point: Inversely proportional to period ​ Period (T) ○​ Definition: Time taken for one complete wave cycle ○​ Units: Seconds (s) ○​ Calculation: T = 1/f (MUST MEMORIZE) ○​ Example: If f = 2 Hz, T = 0.5 seconds ○​ Key point: Time between consecutive wave peaks ​ Wave Speed (v) ○​ Definition: Distance traveled by wave per second ○​ Units: Meters per second (m/s) ○​ Universal constant: Light speed = 3 × 10⁸ m/s ○​ Calculation: v = fλ (MUST MEMORIZE) ○​ Examples: ​ Sound in air = 343 m/s ​ Sound in water = 1,480 m/s ​ Light in vacuum = 3 × 10⁸ m/s Key Equations ​ v = fλ (Wave speed = frequency × wavelength) ​ f = 1/T (Frequency = 1/period)  PHYSIC MIDTERM EXAM 2025 4. Reflection and Refraction Reflection and Refraction (ESSENTIAL CONCEPTS) Reflection (MUST MEMORIZE) 1.​ Law of Reflection: ○​ Angle of incidence = Angle of reflection ○​ Measured from normal line ○​ Always true for all waves ○​ Works for all surfaces 2.​ Mirror Types: ○​ Plane Mirrors: ​ Image same size as object ​ Image appears behind mirror ​ Image virtual and upright ​ Image laterally inverted ​ Distance behind = Distance in front ○​ Curved Mirrors: ​ Can magnify or reduce ​ Real or virtual images ​ Used in telescopes/microscopes 3.​ Total Internal Reflection (TIR): ○​ Conditions (MUST KNOW): ​ Light traveling from denser to less dense medium ​ Angle of incidence > critical angle ​ No refraction occurs ​ 100% reflection ○​ Critical Angle Formula: ​ n = 1/sin(c) [MEMORIZE] ​ c = critical angle ​ n = refractive index ○​ Total Internal Reflection Applications (REQUIRED KNOWLEDGE)​ Understanding these applications is crucial for exam questions about real-world uses of TIR: 1.​ Fiber Optics (MUST UNDERSTAND): ○​ How it works: ​ Light travels down glass/plastic fiber ​ Angle of incidence > critical angle ​ Light bounces along inside fiber ​ Almost no energy loss ○​ Key exam points:  PHYSIC MIDTERM EXAM 2025 ​ Light must enter at correct angle ​ Works because n(glass) > n(cladding) ​ Signal can travel many kilometers ​ Used in telecommunications and internet 2.​ Prisms (MUST UNDERSTAND): ○​ How it works: ​ Light enters glass prism ​ Hits back surface at angle > critical angle ​ Reflects 90° or 180° depending on prism type ○​ Key exam points: ​ Used in binoculars and periscopes ​ More efficient than mirrors (100% reflection) ​ No coating needed unlike mirrors ​ Creates spectrum with white light 3.​ Diamond Brilliance (BASIC UNDERSTANDING): ○​ How it works: ​ Critical angle in diamond = 24.4° ​ Most light hitting back faces reflects ​ Multiple internal reflections occur ​ Light exits from top of diamond ○​ Key exam points: ​ Lower critical angle = more sparkle ​ Diamond's high refractive index (2.42) is crucial ​ Cut of diamond maximizes TIR ​ Example of natural TIR application 4.​ Endoscopes (BASIC UNDERSTANDING): ○​ How it works: ​ Bundle of optical fibers ​ Light travels by TIR down each fiber ​ Image transmitted fiber by fiber ​ Flexible due to thin fibers ○​ Key exam points: ​ Each fiber carries one point of image ​ Uses coherent fiber bundles ​ Requires illumination fibers ​ Medical/industrial inspection use Remember: For the exam, focus on explaining how TIR makes each application possible. You should be able to: ​ Draw ray diagrams showing TIR in each case ​ Explain why critical angle is important ​ Link refractive index to how well TIR works ​ Describe practical advantages over other methods  PHYSIC MIDTERM EXAM 2025 Refraction (REQUIRED KNOWLEDGE) 1.​ Snell's Law: ○​ Formula: n₁sin(θ₁) = n₂sin(θ₂) [MEMORIZE] ○​ n = refractive index ○​ θ = angle to normal 2.​ Refractive Index: ○​ Formula: n = c/v [MEMORIZE] ○​ c = speed of light in vacuum ○​ v = speed in medium ○​ Always > 1 for real materials 3.​ Common Values (MEMORIZE): ○​ Air: ≈ 1.0 ○​ Water: 1.33 ○​ Glass: 1.5-1.9 ○​ Diamond: 2.42 4.​ Effects (UNDERSTAND ALL): ○​ Bending of light ○​ Apparent depth ○​ Rainbows ○​ Mirages 5. Sound and Electromagnetic Spectrum Sound Waves ​ Properties: ○​ Longitudinal waves that require a medium ○​ Created by vibrating objects ○​ Cannot travel through vacuum ○​ Speed in air ≈ 343 m/s (room temperature) ○​ Speed increases in denser media (faster in water than air) ​ Wave Characteristics: ○​ Frequency determines pitch (higher frequency = higher pitch) ○​ Amplitude determines loudness ○​ Period (T) = 1/frequency ○​ Wavelength = speed/frequency ​ How Musical Instruments Work: ○​ Strings: Vibration creates sound waves ○​ Wind: Air column vibration ○​ Percussion: Surface vibration ○​ Key factors: Length, tension, thickness affect pitch  PHYSIC MIDTERM EXAM 2025 Electromagnetic Spectrum (MUST MEMORIZE IN ORDER) From shortest to longest wavelength (highest to lowest frequency): 1.​ Gamma Rays ○​ Shortest wavelength (30 EHz) ○​ Most energetic ○​ Sources: Radioactive decay, nuclear reactions ○​ Applications: Cancer treatment, sterilization 2.​ X-Rays ○​ Wavelength: 0.01-10 nanometers ○​ Frequency: 30 PHz - 30 EHz ○​ Applications: Medical imaging, security scanning ○​ Can penetrate soft tissue but absorbed by bones 3.​ Ultraviolet (UV) ○​ Wavelength: 10-380 nanometers ○​ Frequency: 790 THz - 30 PHz ○​ Three types: UVA, UVB, UVC ○​ Source: Sun ○​ Can cause skin damage but needed for vitamin D 4.​ Visible Light ○​ Wavelength: 380-700 nanometers ○​ Frequency: 430-790 THz ○​ Color spectrum: ROYGBIV ​ Red ​ Orange ​ Yellow ​ Green ​ Blue ​ Indigo ​ Violet 5.​ Infrared (IR) ○​ Wavelength: 700 nanometers - 1 millimeter ○​ Frequency: 300 GHz - 430 THz ○​ Thermal radiation ○​ Applications: Night vision, thermal imaging ○​ Felt as heat 6.​ Microwaves ○​ Wavelength: 1 millimeter - 1 meter ○​ Frequency: 300 MHz - 300 GHz ○​ Applications: Communications, cooking ○​ Can cause molecular rotation (heating) 7.​ Radio Waves  PHYSIC MIDTERM EXAM 2025 ○​ Longest wavelength (>1 meter) ○​ Lowest frequency (