11th Physics Material Tamil Medium

Explanation: When a body rolls without slipping, total kinetic energy K = K_{translational} + K_rotational. For K_{translational} = K_rotational, the Mass distribution must satisfy I = mR²/2. Among common shapes, only a Solid sphere meets this criterion.

Analogy: A Solid ball rolls down smoothly; its rotational and translational energies are balanced.

Hint: Consider which shape has a moment of inertia I = (2/5)mR².

Explanation: power P = τω, where τ is torque, ω is angular velocity. Convert rev/min to rad/s: ω = 2π × 1800 / 60 = 188.5 rad/s. Torque τ = P / ω. Using the given power, the torque can be calculated in Nm.

Analogy: Engine power is like the “push” distributed over rotational speed.

Hint: Use τ = P / ω and convert rev/min to rad/s first.

Explanation: Angular momentum L = Iω is conserved when no external torque acts. If I decreases by 40%, ω must increase proportionally: ω_new = ω_old × (I_old/I_new) = 180 × (1/0.6) = 300 rpm.

Analogy: Figure skaters spin faster when pulling arms in.

Hint: Apply conservation of angular momentum: Iω = constant.

Explanation: Scalar quantities have magnitude only, no direction. Angular momentum, force, and velocity are Vectors. Electrostatic potential is scalar because it is a measure of energy per unit charge without direction.

Analogy: Temperature is scalar, wind speed is Vector.

Hint: Look for quantity with magnitude but no specific direction.

Explanation: Moment of inertia I depends on Mass distribution relative to the rotation axis. It is independent of the body’s angular velocity. Shape, Mass distribution, and axis of rotation influence I, but angular speed does not.

Analogy: Spinning a wheel faster does not change its Mass distribution.

Hint: Consider what does not affect I: angular velocity, shape, or Mass distribution?

Explanation: Kinetic Theory: K_avg = (3/2) k_B T. Average kinetic energy depends only on absolute temperature, not on Molecule Mass or environmental temperature.

Analogy: Heating a gas increases Molecular motion, independent of surrounding conditions.

Hint: energy depends on the thermodynamic temperature (Kelvin scale).

Explanation: First law states ΔU = Q − W, a statement of energy conservation. It relates Heat added to a system and work done to internal energy changes, generalizing energy conservation.

Analogy: Like tracking Money in/out of a wallet: total remains conserved.

Hint: Think in terms of conservation of energy principle.

Explanation: At extremely low temperatures, some materials exhibit zero resistance, known as superconductors. Semiconductors, perfect conductors, and dielectrics behave differently.

Analogy: Like a frictionless path for Electricity.

Hint: Materials that conduct without resistance at very low temperatures.

Explanation: At high altitudes, atmospheric pressure is low, reducing water’s boiling point. Cooking rice takes longer on mountains than at sea level. Sea-level or underground conditions have normal or higher boiling points.

Analogy: Water boils faster at lower pressures, so cooking slows.

Hint: Consider how pressure affects water boiling point at high altitude.

Explanation: Water reaches maximum density at 4°C. At 0°C, it starts freezing, and at 25°C or 100°C, density decreases due to thermal expansion.

Analogy: Water expands slightly when heated or frozen.

Hint: Think of the temperature at which water is densest.

Explanation: Elasticity refers to the ability to return to original shape after deformation. Steel requires a large deforming force but returns to its original shape, whereas rubber deforms easily and has lower elastic modulus.

Analogy: Steel spring snaps back with more force; rubber stretches easily.

Hint: Consider which material has a higher modulus of elasticity.

Explanation: Surface tension arises from cohesive forces at the liquid-air interface. It allows Light objects like needles to float if placed carefully, despite being denser than water.

Analogy: Surface tension acts like a “skin” on water that supports small insects.

Hint: Think about what prevents small objects from sinking despite their weight.

Explanation: The tension in the string acts perpendicular to the pendulum’s displacement at all times. work W = F × d × cosθ. Since θ = 90° between force and displacement, work done is zero.

Analogy: Pushing sideways against a swinging pendulum does no work along its path.

Hint: Consider the direction of tension relative to pendulum motion.

Explanation: SHM occurs when restoring force is proportional to displacement: F = −kx. Both inertia and elasticity are needed: inertia resists motion, elasticity provides restoring force. External force is not necessary.

Analogy: Spring-Mass system oscillates due to spring stiffness and mass inertia.

Hint: SHM requires both mass and a restoring mechanism.

Explanation: Clouds consist of tiny water droplets or ice crystals. Their density is much lower than surrounding air, allowing them to remain suspended in the Atmosphere.

Analogy: Small feathers float in air due to low density.

Hint: Focus on the property that allows objects to stay suspended in air.

Explanation: Dimensions: M = mass, L = length, T = time. work/energy = force × distance. Force = M × L/T². Multiplying by distance L gives M × L² / T² for work. Here, M × L × T² is a different dimension.

Analogy: Dimension analysis helps check physical formulas.

Hint: Match dimensions with force, velocity, acceleration, or work.

Explanation: Materials like Mica conduct Heat well due to atomic vibrations but do not allow free electron flow, making them electrical insulators. Rubber and celluloid are poor conductors of both.

Analogy: Stove-top insulator conducts Heat to pan without conducting Electricity.

Hint: Look for a thermal conductor that is electrically insulating.

Explanation: Many remote-sensing devices use infrared radiation to detect Heat signatures and map surfaces. Gamma rays, UV, and X-rays are unsuitable for general remote sensing due to absorption or danger.

Analogy: IR cameras detect body Heat like night-vision goggles.

Hint: Think about detecting thermal emissions from objects.

Explanation: Archimedes’ principle: buoyant force = weight of Fluid displaced. It depends on the mass/volume of displaced Fluid, not on the body’s mass or shape directly.

Analogy: Boat floats because it displaces enough water to balance its weight.

Hint: Consider the principle of Fluid displacement.

Explanation: A moving body always has kinetic energy, momentum, and velocity. Potential energy depends on position in a force field (e.g., height in gravity). If reference height = 0, potential energy can be zero.

Analogy: A rolling ball on flat ground has no gravitational potential energy.

Hint: Identify a form of energy that depends on position rather than motion.

Explanation: Capillary action occurs due to adhesive forces between liquid and Solid surfaces, pulling liquid up narrow tubes. Gravitation, buoyancy, or floating are unrelated mechanisms here.

Analogy: Water rises in a thin straw via capillary forces.

Hint: Look for the phenomenon causing liquids to climb narrow spaces.

Explanation: Sun emits vast amounts of energy across the Spectrum. Wood, coal, and Moon are far smaller or indirect sources of Heat for Earth.

Analogy: Sunlight warms the Earth daily.

Hint: Think of the star that radiates energy to Earth.

Explanation: Ohm’s law: V = IR, formulated by Georg Ohm. Gauss, Newton, and Faraday worked in Magnetism, mechanics, and electromagnetism.

Analogy: Ohm quantified how voltage, current, and resistance relate.

Hint: Focus on the physicist who related current and voltage mathematically.

Explanation: Tyndall effect is Light scattering by colloidal particles. Suspensions scatter Light, while reflection, refraction, and dispersion involve different optical phenomena.

Analogy: Dust in sunlight beams makes Light visible due to scattering.

Hint: Think of visible Light scattering in colloids.

Explanation: In visible Light, red has the longest wavelength (~700 nm), followed by yellow, green, and violet (~400 nm). Longer wavelength means less bending in refraction.

Analogy: Red Light spreads least in a prism compared to violet.

Hint: Think of the color at the “warm” end of the Spectrum.

Explanation: Earth’s magnetic north pole is actually a magnetic south pole, located near the geographical north. Compass needles point toward it. East, west, and south are incorrect.

Analogy: A compass needle points toward magnetic north (geographical north).

Hint: Consider how a compass needle aligns with Earth’s magnetic field.

Explanation: Primary colors in additive light are red, green, and blue. Yellow is a secondary color, made by mixing red and green.

Analogy: Mixing red and green light gives yellow in a display screen.

Hint: Identify the color that is a combination of others.

Explanation: Magnetic flux Φ = B × A; SI unit is Weber (Wb). Weber/m, Weber/m², or Weber × m are incorrect.

Analogy: Magnetic flux is like the total number of magnetic field lines through an area.

Hint: Focus on the SI unit used in electromagnetism for total field through a surface.

Explanation: Absorbing all visible light means no light is reflected; the object looks black. White reflects all colors, blue reflects mainly blue.

Analogy: Black clothes absorb sunlight, warming up.

Hint: Consider the color seen when no light is reflected.

Explanation: Fresh water freezes at 0°C at 1 atm pressure. Other temperatures listed are incorrect.

Analogy: Ice cubes form at 0°C in a freezer.

Hint: Standard freezing temperature in Celsius scale.

Explanation: An α-particle consists of 2 protons and 2 neutrons, which is a helium nucleus. Oxygen, lithium, or hydrogen nuclei are different.

Analogy: Alpha particle = helium nucleus stripped of electrons.

Hint: Contains 2 protons and 2 neutrons.

Explanation: Tesla (T) measures magnetic flux density (B), not flux (Weber), field strength (H), or moment.

Analogy: Tesla indicates how “strong” the magnetic field is in a given area.

Hint: Think of the strength of a magnetic field per unit area.

Explanation: Mirage occurs due to refraction and total internal reflection of light in layers of air with different temperatures and densities. Not polarization, interference, or Diffraction.

Analogy: Hot pavement bends light to make water-like illusions.

Hint: Look for bending of light in varying air densities.

Explanation: Concave or parabolic mirrors focus light into a beam; plane or convex mirrors do not. Headlights use parabolic shape to direct light effectively.

Analogy: A flashlight reflector directs light forward.

Hint: Think of a mirror that converges light into a strong beam.

Explanation: Iron is ferromagnetic and responds strongly to magnetic fields. Silver, gold, and mercury are non-magnetic.

Analogy: Magnets attract iron nails, not gold coins.

Hint: Choose a common ferromagnetic metal.

Explanation: Plane mirrors produce virtual, upright, same-size images behind the mirror. Real images form with lenses or concave mirrors.

Analogy: Your reflection in a bathroom mirror is virtual.

Hint: The image cannot be projected on a screen.

Explanation: Transformers use mutual induction: Alternating Current in primary coil induces EMF in secondary coil. Generators, self-induction, and inverters are different devices.

Analogy: Magnetic field transfer induces voltage in nearby coil.

Hint: Focus on how AC in one coil induces voltage in another.

Explanation: Energy of EM radiation E = hν. Microwave frequency is lowest among options, so energy is least. UV, visible, gamma have higher frequencies.

Analogy: Microwave photons carry less energy than gamma photons.

Hint: Look for the electromagnetic wave with lowest frequency.

Explanation: Viscosity measures Fluid’s resistance to flow. Among water, milk, oil, and petrol, oil is thickest and flows slowest.

Analogy: Honey flows slower than water due to higher viscosity.

Hint: Think about which liquid “flows the slowest.”

Explanation: Star color is determined by surface temperature. Hot stars appear blue/white, cooler stars appear red. Radius, pressure, or distance do not directly determine color.

Analogy: Heating a metal rod changes its color from red to white.

Hint: Color indicates the thermal energy of a star’s surface.

Explanation: Resistance R = ρL/A. Doubling length L doubles resistance (R ∝ L) if cross-sectional area remains same.

Analogy: A longer pipe is harder for water to flow through, similar to current.

Hint: Resistance is directly proportional to length.

Explanation: Slope = Δv/Δt, which equals acceleration. Distance is area under the graph, speed is magnitude of velocity, displacement is NET distance.

Analogy: A steeper velocity-time slope indicates faster acceleration, like pressing the gas pedal harder.

Hint: Think of the rate of change of velocity over time.

Explanation: Convex mirrors diverge light, providing a wider field of view, making them “saving mirrors” on vehicles. Plane, concave, parabolic mirrors serve other purposes.

Analogy: Rearview mirrors are convex to see more traffic behind.

Hint: Choose the mirror that increases field of view safely.

Explanation: Seismograph detects ground motion during earthquakes. Richter measures magnitude, hygrometer measures humidity, lactometer measures milk density.

Analogy: Seismograph is like a pen that traces tremors on paper.

Hint: Focus on detecting seismic vibrations.

Explanation: Tungsten has high melting point (~3400°C), making it ideal for filaments. Copper, lead, or nichrome either melt easily or are unsuitable.

Analogy: Tungsten filament glows without melting when current passes.

Hint: Look for a material with very high melting point.

Explanation: Planck constant h relates energy and frequency: E = hν. Dimension: angular momentum = M L² T⁻¹.

Analogy: h “quantizes” energy in discrete packets of motion.

Hint: Check which physical quantity has dimensions M L² T⁻¹.

Explanation: Light year = distance traveled by light in one year. It is not time, speed, or intensity.

Analogy: Like measuring the “distance” light covers in a year-long journey.

Hint: Relates to space distance, not speed or time.

Explanation: Petrol has lower density than water, mercury, and Salt water. Density affects buoyancy and floating.

Analogy: Petrol floats on water due to lower density.

Hint: Consider which liquid is lightest for a given volume.

Explanation: Microwaves Heat Food by causing water molecules to vibrate. UV, X-rays, radio waves are unsuitable for cooking.

Analogy: Microwave oven excites molecules, generating heat inside Food.

Hint: Think of electromagnetic waves that excite water molecules to heat Food.

Explanation: Steel has higher modulus of elasticity than plastic, rubber, or wet clay. Elasticity is ability to regain shape after deformation.

Analogy: Steel spring snaps back firmly; rubber stretches more easily but less stiff.

Hint: Look for the material that resists deformation the most.

Explanation: Resolution refers to clarity and detail in display. Color and graphics affect appearance, but sharpness is specifically resolution.

Analogy: Higher pixel count = higher resolution = sharper image.

Hint: Think of number of pixels defining image clarity.

Explanation: Water has highest specific heat (~4.18 J/g°C) among common substances. Lead, copper, glass store less heat per unit mass per °C.

Analogy: Water heats and cools slowly compared to Metals.

Hint: Look for the substance that requires most energy to raise 1 g by 1°C.

Explanation: Mass = quantity of Matter. Density = mass/volume, weight = gravitational force, volume = space occupied.

Analogy: Steel ball has same Matter quantity anywhere, mass is intrinsic.

Hint: Intrinsic measure of Matter irrespective of gravity.

Explanation: Uranium undergoes fission, releasing energy to generate Electricity. Coal, radium, diesel are unsuitable for fission reactors.

Analogy: Uranium atoms split to release energy like tiny bombs.

Hint: Think of fissile material used in power reactors.

Explanation: Rectifiers use diodes to allow current in one direction, converting AC → DC. Dynamo generates AC, transformers change voltage, oscillators produce AC signals.

Analogy: Rectifier acts like a one-way valve for electrons.

Hint: Device that allows current in only one direction.

Explanation: Anemometer measures wind speed; some types also estimate wind force. Audiometer measures hearing, ammeter measures current, altimeter measures height.

Analogy: Pinwheels spin faster in stronger winds.

Hint: Focus on an instrument for wind measurement.

Explanation: Sudden drop = storm or cyclone formation. Gradual pressure changes relate to rain or fair weather. Cold weather is unrelated to sudden drop.

Analogy: Rapidly falling barometer = approaching storm.

Hint: Look for low pressure indicating strong weather events.

Explanation: Escape velocity v = √(2GM/R) ≈ 11 km/s for Earth. It’s the speed to overcome Earth’s gravity without further propulsion.

Analogy: Throwing a ball so hard it never comes back.

Hint: Slightly more than 10 km/s for Earth’s gravity.

Explanation: Chemical energy is stored in rechargeable batteries and converts to electrical energy when used. Kinetic or potential energy are not stored directly.

Analogy: Battery = compressed spring storing energy to release.

Hint: Energy released as Electricity comes from chemical reactions.

Explanation: Violet has shortest wavelength; deviation ∝ refractive index ∝ 1/λ. Red deviates least, violet most.

Analogy: Prism separates colors like rainbow.

Hint: Shortest wavelength in visible Spectrum deviates most.

Explanation: Fermimeter (~10⁻¹⁵ m) is smaller than micron, nanometer, angstrom. Used in nuclear Physics.

Analogy: Fermimeter ≈ size of atomic nucleus.

Hint: Roughly the size of a proton or neutron.

Explanation: Sonar uses sound waves to detect underwater objects. Radar detects above water/air; pulsars/quasars are astronomical.

Analogy: Submarine uses sonar to “see” obstacles.

Hint: Uses sound waves under water.

Explanation: RH = (actual vapor/saturation) × 100. Higher temperature increases saturation, so RH decreases if moisture stays constant.

Analogy: Warm air “absorbs” moisture, feels drier.

Hint: Warmer air holds more water; RH drops.

Explanation: Johannes Kepler formulated laws: elliptical orbits, equal area in equal time, period related to radius. Newton and Galileo studied gravity/motion; Copernicus heliocentric theory.

Analogy: Kepler mapped precise planetary paths.

Hint: Laws describe planetary orbits mathematically.

Explanation: Laser is coherent, monochromatic, and directional. Maser emits microwaves.

Analogy: Laser = flashlight beam but extremely thin and focused.

Hint: Think of highly focused light with minimal divergence.

Explanation: Microwaves penetrate the Atmosphere with minimal loss, ideal for satellite Communication. Infrared, UV, and millimeter waves are less practical.

Analogy: Satellite dishes use microwave frequencies.

Hint: Electromagnetic wave with long wavelength for space transmission.

Explanation: Microphones convert vibrations (sound) into electrical signals. Loudspeakers do opposite; Solar cells convert light; gramophones are mechanical playback.

Analogy: Microphone acts like a translator of sound to Electricity.

Hint: Device that converts acoustic energy to electrical signals.

Explanation: Air flow occurs at constant pressure (isobaric). Isothermal = constant temperature, adiabatic = no heat exchange, isochoric = constant volume.

Analogy: Blowing through a straw keeps pressure roughly constant.

Hint: Process occurs without significant pressure change.

Explanation: Light year = distance light travels in one year. Cosmic km, galactic unit, stellar mile are nonstandard.

Analogy: Light-year = cosmic measuring tape.

Hint: Long astronomical distances use light travel per year.

Explanation: Ionosphere reflects radio waves back to Earth. Troposphere = weather, stratosphere = ozone layer, chromosphere = Sun’s layer.

Analogy: Radio waves bounce like tennis balls off ionosphere layer.

Hint: Layer that bends radio waves for long-distance Communication.

Explanation: Steel’s high elasticity allows it to absorb shocks without permanent deformation. Low elasticity materials fail to absorb impact efficiently.

Analogy: Steel spring in car suspension compresses and rebounds effectively.

Hint: Look for a material that can deform elastically and return to shape.

Explanation: Nuclear fission splits heavy atoms (uranium) releasing energy. Fusion combines light atoms; cold fusion/superconductivity are unrelated to power generation.

Analogy: Atom splitting releases enormous energy like a tiny explosion.

Hint: Process involves splitting heavy nuclei.