Understanding Noise and Vibration: Key Concepts
Noise
Noise: A wave that moves through air and water (partially elastic medium). We perceive it as sound pressure.
Sound Pressure and Levels
Sound Pressure Variations: Measured as Sound Pressure Level (SPL) in decibels (dB).
Pressure = Force / Area = Newton / meter2 = Pascal.
- Audible Field: To produce an auditory sensation, the frequency must be between 20 and 20,000 Hz.
- Pain Threshold: 120 dB, equivalent to 20 N/m2 = 20 Pa.
- Perception Threshold: 2 x 10-5 Pa, or 0 dB.
Sound Wave Characteristics
Sound Velocity:
Read MoreElectric Potential and Energy: Problems & Solutions
Electric Potential Energy Change: Electron in Thunderstorm
During a thunderstorm, the electric potential difference between a cloud and the ground is Vcloud – Vground = 1.3 x 108 V, with the cloud being at the higher potential. What is the change in an electron’s electric potential energy when the electron moves from the ground to the cloud?
Work Done by Electric Force on a Sodium Ion
Suppose that the electric potential outside a living cell is higher than that inside the cell by 0.070 V. How much
Kirchhoff’s Laws and Stellar Properties
Kirchhoff’s Laws
Kirchhoff’s Laws describe the behavior of light interacting with matter, resulting in different types of spectra:
- Law 1: Continuous Spectrum: A solid, liquid, or dense gas excited to emit light will radiate at all wavelengths, producing a continuous spectrum.
- Law 2: Emission Spectrum: A low-density gas excited to emit light will do so at specific wavelengths, producing an emission spectrum.
- Law 3: Absorption Spectrum: If light comprising a continuous spectrum passes through a cool,
Electrostatics and Electromagnetism: Basic Concepts
Electrostatic Induction
Electrostatic induction is a method used to charge a conductor without putting it into contact with an electrified object.
Coulomb’s Law
Using a torsion balance, Coulomb found that the force of attraction or repulsion between two point charges (charged bodies whose dimensions are negligible compared with the distance r that separates them) is inversely proportional to the square of the distance between them.
Electric Field Flux
The electric flux is related to the force of attraction
Read MoreAdrian Mole’s Teenage Years: A 1980s Diary
Summary
The Secret Diary of Adrian Mole, Aged 13 ¾ begins when Adrian is 13 ¾ and ends on his fifteenth birthday. During this time, Adrian experiences first love, navigates his parents’ marital problems, and pursues his ambition to become an intellectual and writer. Pandora, the love of his life, is more intelligent than Adrian, and her family is wealthier. She falls for Adrian after he rebels by wearing red socks to school instead of the required black. Together, they form a committee to continue
Read MoreAncient Greek Astronomers and Mathematicians
Apollonius
Apollonius was a great mathematician who discovered conic sections (curves obtained by cutting a cone with a plane). He also explained the retrograde motion of the planets using epicycles.
Meton
Meton discovered the Metonic cycle (19 years = 235 lunar months) to predict eclipses of the sun and moon, which recur every 19 years. The sun cycle coincides with the moon cycle every 19 years with few exceptions.
Eratosthenes
Eratosthenes discovered the Sieve of Eratosthenes to calculate prime numbers.
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