Kerala SSLC Physics cheat sheet

Heating effect: heat H = I²Rt (joule); power P = VI = I²R = V²/R.

Joule's law: heat produced in a resistor is proportional to I², R and t.

1 unit of electrical energy = 1 kWh = 3.6 × 10⁶ J.

Fuse is connected in series in the live wire; it melts when current exceeds its rating.

Short circuit: live and neutral touch directly, resistance falls, current rises sharply.

Overloading: too many appliances on one circuit draw current above the safe rating.

Electric iron, heater, filament lamp work on the heating effect; filament uses high-melting-point tungsten.

Chemical effect: current through an electrolyte causes electrolysis; used in electroplating.

Right-hand grip rule: thumb along current, curled fingers give the magnetic field direction.

Field of a straight conductor: concentric circles; strength increases with current, decreases with distance.

Solenoid with current behaves like a bar magnet; field inside is uniform and parallel.

Electromagnet: soft iron core inside a coil; magnetism disappears when current stops.

Fleming's left-hand rule (motor): forefinger = field, middle finger = current, thumb = force/motion.

Fleming's right-hand rule (generator): forefinger = field, thumb = motion, middle finger = induced current.

Force on a conductor is maximum when current is perpendicular to the field, zero when parallel.

In a motor, the split-ring commutator reverses current direction every half rotation.

Faraday's law: induced emf equals the rate of change of magnetic flux through the coil.

Lenz's law: induced current opposes the change producing it (conservation of energy).

Induced current appears only while the flux through the coil changes, not when it is steady.

Moving a magnet into a coil or moving the coil across a field both induce emf.

AC generator: coil rotating in a magnetic field; slip rings keep the external circuit connected.

DC generator uses a split-ring commutator to give unidirectional output.

Increasing turns, field strength or rotation speed increases the induced emf.

Transformer works on mutual induction and needs alternating current; it cannot work on DC.

Laws of reflection: angle of incidence = angle of reflection; incident ray, reflected ray and normal lie in one plane.

For a plane mirror: image is virtual, erect, laterally inverted, same size, as far behind as the object is in front.

Spherical mirror formula: 1/f = 1/v + 1/u; magnification m = -v/u = h'/h (sign convention).

Concave mirror: f = R/2; converging; real image for object beyond focus, virtual and enlarged within focus.

Convex mirror: diverging; always virtual, erect, diminished; wide field of view, used as rear-view mirror.

Snell's law: n₁ sin i = n₂ sin r; refractive index n = sin i / sin r = c/v.

Light bends toward the normal entering a denser medium and away from it entering a rarer medium.

Total internal reflection occurs when light travels from denser to rarer medium and i exceeds the critical angle.

White light splits into VIBGYOR on passing through a prism; violet bends most, red least.

Cause of dispersion: refractive index depends on wavelength, so each colour has a different deviation.

Rainbow forms by refraction, dispersion and total internal reflection in raindrops, with the sun behind the observer.

Rayleigh scattering: intensity ∝ 1/λ⁴, so shorter (blue) wavelengths scatter more strongly.

Sky appears blue because blue light is scattered most by air molecules.

Sun appears red at sunrise and sunset because blue light is scattered away over a long atmospheric path.

Clouds appear white because large water droplets scatter all wavelengths almost equally.

Red is used for danger signals because it scatters least and travels farthest through the atmosphere.

Wave speed v = fλ; frequency f = 1/T; SI unit of frequency is hertz (Hz).

Longitudinal waves: particles vibrate along the direction of propagation; sound in air is longitudinal.

Sound needs a material medium; it cannot travel through vacuum.

Speed of sound in air ≈ 340 m/s at room temperature, faster in solids and liquids than in gases.

Audible range for humans is 20 Hz to 20,000 Hz; above is ultrasonic, below is infrasonic.

Pitch depends on frequency; loudness depends on amplitude; quality depends on waveform/overtones.

Echo: reflected sound heard separately if the reflecting surface is at least about 17 m away.

Reverberation is the persistence of sound due to repeated reflection in a hall; absorbed by curtains and carpets.

Work W = F s cos θ; SI unit joule (J); work is zero when force is perpendicular to displacement.

Kinetic energy KE = ½mv²; potential energy PE = mgh near Earth's surface.

Work-energy theorem: net work done on a body equals the change in its kinetic energy.

Power P = W/t = Fv; SI unit watt (W); 1 kW = 1000 W.

Law of conservation of energy: energy is neither created nor destroyed, only transformed.

1 horsepower ≈ 746 W; commercial unit of energy is kWh.

Energy of a stretched spring: E = ½kx².

In free fall, potential energy converts to kinetic energy, total mechanical energy staying constant (ignoring friction).

Heat is energy in transit due to temperature difference; SI unit joule; temperature in kelvin.

Q = mcΔT for sensible heating; c is specific heat capacity, water ≈ 4200 J kg⁻¹ K⁻¹.

Latent heat: Q = mL; melting ice L ≈ 3.34 × 10⁵ J/kg, steam condensation L ≈ 2.26 × 10⁶ J/kg.

Temperature in K = temperature in °C + 273.

Conduction needs a medium and no bulk movement; convection is bulk movement in fluids; radiation needs no medium.

Thermal equilibrium: no net heat flow once two bodies reach the same temperature.

Water has unusually high specific heat, so it is used as a coolant and moderates climate.

Black surfaces are good absorbers and good emitters of radiation; shiny surfaces reflect it.

Record readings to the least count of the instrument; metre scale 0.1 cm, vernier 0.01 cm, screw gauge 0.01 mm.

Zero error must be checked and applied as a correction before calculating results.

Take repeated readings and use the mean to reduce random error.

In Ohm's law experiment, connect ammeter in series and voltmeter in parallel across the resistor.

Plot the V-I graph through the origin; slope gives resistance R = V/I.

In a mirror experiment, place the object pin and image pin so that parallax is removed before measuring.

Draw ray diagrams with at least two rays and mark arrows on rays to show direction.

Report results with units and the correct number of significant figures.