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ChemistryClass 12CBSE
Why Pure Water Barely Conducts but Salt Water Does
Calculate conductivity, cell constant and molar conductivity from measured resistance, see how molar conductivity changes on dilution for strong and weak electrolytes, apply Kohlrausch's law, and solve Faraday's law problems on electrolysis.
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Why Zinc Gives Up Its Electrons to Copper in a Cell
Compare galvanic and electrolytic cells and write cell notation, use standard electrode potentials to find cell emf and predict feasibility, apply the Nernst equation at any concentration, and link emf to Gibbs energy and the equilibrium constant.
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Why Sea Water Freezes at a Lower Temperature Than Tap Water
Use relative lowering of vapour pressure, boiling point elevation and freezing point depression to find molar masses, apply osmotic pressure and reverse osmosis, and correct for dissociation and association with the van't Hoff factor.
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Why a Soda Bottle Fizzes the Moment You Open It
Express concentration in every common unit and convert between them, apply Henry's law to gas solubility, use Raoult's law for vapour pressure, and tell ideal from non-ideal solutions with their positive and negative deviations and azeotropes.
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How a Phone Charger Turns AC Into DC
See how a p-n junction forms with its depletion region and potential barrier, interpret a diode's I-V characteristics in forward and reverse bias, and use junction diodes as half-wave and full-wave rectifiers.
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Why a Pinch of Impurity Makes Silicon Conduct
Classify metals, semiconductors and insulators by their energy bands, see how electrons and holes carry current in a pure semiconductor, and learn how doping creates n-type and p-type semiconductors with majority and minority carriers.
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Why Splitting and Joining Nuclei Both Release Energy
Find the size and density of nuclei with R = R0A^(1/3), calculate mass defect and binding energy, read the binding energy per nucleon curve, and see how the nuclear force, fission and fusion fit together.
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Why Most Alpha Particles Fly Straight Through Gold Foil
Work through alpha-particle scattering and the nuclear model with distance of closest approach, see why Rutherford's model needed Bohr's postulates, derive the radius and energy of hydrogen orbits, and explain its line spectrum with de Broglie waves.
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How Light Can Behave Like Both a Wave and a Particle
See why the wave theory fails to explain the photoelectric effect, use Einstein's photoelectric equation, learn the properties of photons, and calculate the de Broglie wavelength of moving particles such as electrons.
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Why Red Light Cannot Knock Electrons Out of Zinc, However Bright
Learn how electrons escape a metal and what work function and threshold frequency mean, go through the key observations of the photoelectric effect, and study how intensity, frequency and potential affect photocurrent and stopping potential.
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How Two Beams of Light Can Add Up to Darkness
Compare coherent and incoherent addition of light waves and the conditions for sustained interference, calculate fringe width in Young's double-slit experiment, and find the width of the central maximum in single-slit diffraction.
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Why Light Slows Down and Bends When It Enters Glass
Understand wavefronts and Huygens principle, then use secondary wavelets to prove the law of reflection and Snell's law of refraction, and see why the wavelength of light changes in a medium while its frequency does not.
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How Two Small Lenses Reveal the Cells in an Onion Peel
Find the magnifying power of a compound microscope, see how a refracting telescope forms an image in normal adjustment, and learn why large telescopes use mirrors, with the Cassegrain reflecting design and its advantages.
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How an Optician Knows Exactly Which Lens You Need
Derive refraction at a single spherical surface and the lens maker's formula, locate images with the thin lens formula and magnification, combine the powers of thin lenses in contact, and relate deviation, prism angle and refractive index for a prism.
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How Light Stays Trapped Inside an Optical Fibre
Use the mirror formula and magnification for spherical mirrors, apply the laws of refraction and refractive index at plane surfaces, find the critical angle for total internal reflection, and see how optical fibres carry light by that effect.
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What Microwaves, X-Rays and Rainbows Have in Common
See why Ampere's circuital law needed a displacement current, learn the properties and transverse nature of electromagnetic waves, and tour the spectrum from radio waves and microwaves to X-rays and gamma rays with their everyday uses.
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How a Radio Picks One Station Out of Many
Use phasors to find the impedance and phase angle of a series LCR circuit, work out the resonant frequency, derive average power and the power factor and understand wattless current, and see how AC generators and transformers work.
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Why a 230 V Household Supply Actually Peaks Above 325 V
Relate the peak and RMS values of alternating current and voltage, represent AC in a resistor with phasors, and find the reactance and the phase relation between current and voltage for a pure inductor and a pure capacitor.
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How Moving a Magnet Through a Coil Creates Electricity
Define magnetic flux and see what the coil-and-magnet experiments of Faraday and Henry reveal, apply Faraday's laws to calculate induced emf and current, use Lenz's law and its link to energy conservation, and derive motional emf and meet self- and mutual inductance.
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Why a Magnet Grabs Iron Nails but Ignores Aluminium Foil
Picture a bar magnet's field lines and see why it behaves like a solenoid, learn the field of a magnetic dipole on its axis and equator and the torque on it, understand magnetisation, magnetic intensity and Gauss's law for magnetism, and compare dia-, para- and ferromagnetic materials.
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How a Galvanometer Becomes Both an Ammeter and a Voltmeter
Apply Ampere's circuital law to a long straight wire, understand the field inside a solenoid, derive the force between parallel currents and the definition of the ampere, and find the torque on a current loop and how a moving coil galvanometer is converted into an ammeter and a voltmeter.
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Why a Compass Needle Swings Near a Current-Carrying Wire
See how Oersted's experiment links electricity and magnetism, find the force on a moving charge in magnetic and electric fields, work out the radius and period of circular motion in a magnetic field, derive the force on a current-carrying wire, and use the Biot-Savart law for a circular loop.
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How Two Simple Rules Can Solve Any Tangled Circuit
Tell the emf of a cell from its terminal voltage and account for internal resistance, combine cells in series and parallel, apply Kirchhoff's junction and loop rules to multi-loop circuits, and use the Wheatstone bridge balance condition to find an unknown resistance.
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Why Electrons Crawl Through a Wire Yet the Light Comes On at Once
Define electric current and picture charge flow in a metal, relate drift velocity and mobility to current with I = neAv_d, apply Ohm's law and see where it fails, and understand resistivity, its temperature dependence, and electrical energy and power.
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