Estonian Basic-School Physics Exam cheat sheet

Average speed v = s/t; average velocity uses displacement, so a round trip returning to the start has zero average velocity but non-zero average speed.

Constant acceleration: v = v0 + at, s = v0t + at²/2, v² = v0² + 2as. Free fall near Earth uses g ≈ 9.8 m/s² downward (often rounded to 10 m/s²).

Newton's second law: F = ma; net force and acceleration point the same way. Newton's third law pairs act on different bodies, so they never cancel each other.

Weight is a force, G = mg (newtons); mass (kilograms) is a measure of inertia and does not change with location.

Friction: static friction adjusts up to a maximum μsN; kinetic friction is approximately μkN and opposes sliding.

Pressure p = F/A in pascals (1 Pa = 1 N/m²). In a liquid, hydrostatic pressure p = ρgh depends only on depth and density, not on container shape.

Work W = Fs·cos α (joules); power P = W/t (watts). Kinetic energy Ek = mv²/2; gravitational potential energy Ep = mgh.

Mechanical energy is conserved when only gravity and elastic forces do work; friction converts mechanical energy into thermal energy.

Moment/lever rule: a lever is balanced when F1·l1 = F2·l2, where l is the perpendicular distance from the pivot to the force line.

Temperature measures the average kinetic energy of particles; it is not the same as the total thermal energy of a body.

Celsius to kelvin: T(K) = t(°C) + 273. Absolute zero is 0 K = −273 °C, where particle motion is minimal.

Heat Q = mcΔT for a temperature change; Q = mλ for melting/freezing and Q = mL for boiling/condensation, where λ and L are specific latent heats.

Specific heat capacity c is the energy needed to raise 1 kg of a substance by 1 K; water's value is about 4200 J/(kg·K), which is unusually large.

Three heat-transfer mechanisms: conduction (mainly in solids, via particle collisions), convection (bulk flow in fluids), radiation (electromagnetic waves, needs no medium).

During a phase change the temperature stays constant although heat is still being supplied; the added energy breaks or forms bonds between particles.

Thermal expansion: Δl = αlΔT for linear expansion; solids and liquids generally expand on heating, and water is densest at about 4 °C.

Gas laws for a fixed amount of gas: pV/T = constant; at constant T, p1V1 = p2V2 (Boyle); at constant p, V/T = constant (Charles).

Good thermal conductors (metals) have free electrons; insulators such as air, foam and wool trap still air and slow conduction and convection.

Current I = Q/t (ampere); conventional current direction is from + to −, opposite to electron drift in metals.

Voltage U = W/Q (volt) is energy per unit charge; it is measured in parallel with a component, current in series.

Ohm's law U = IR holds for metallic conductors at constant temperature; a filament lamp's resistance rises as it heats.

Series circuit: I is the same everywhere, U splits, R total = R1 + R2 + …; parallel circuit: U is the same, I splits, 1/R = 1/R1 + 1/R2 + …

Electrical power P = UI = I²R = U²/R; energy consumed E = Pt, domestic energy often billed in kilowatt-hours (1 kWh = 3.6 MJ).

A fuse or circuit breaker interrupts the circuit when current exceeds a safe value; it is connected in series with the load.

Magnetic field lines run from the north pole to the south pole outside a magnet; a current-carrying wire produces a circular magnetic field around it.

A force acts on a current-carrying conductor in a magnetic field (F = BIl sin α); this is the basis of electric motors and loudspeakers.

Electromagnetic induction: a changing magnetic field through a coil induces a voltage; generators convert mechanical energy into electrical energy this way.

Wave quantities: v = fλ; frequency f is set by the source, while speed and wavelength change when a wave enters a new medium.

Law of reflection: the angle of incidence equals the angle of reflection, both measured from the normal.

Refraction: light bends toward the normal when entering a denser medium (slower speed) and away from it when leaving; Snell's law n1 sin α1 = n2 sin α2.

Total internal reflection occurs only when light travels from a denser to a less dense medium and the angle of incidence exceeds the critical angle.

A plane mirror forms a virtual, upright image the same size as the object, as far behind the mirror as the object is in front.

Converging (convex) lens: parallel rays meet at the focal point; 1/f = 1/a + 1/b. Object beyond 2f gives a real, inverted, diminished image.

Diverging (concave) lens always gives a virtual, upright, diminished image; it is used to correct short-sightedness (myopia).

Sound is a longitudinal mechanical wave needing a medium; it travels about 340 m/s in air at room temperature and faster in water and steel.

Pitch corresponds to frequency, loudness to amplitude; the audible range for young humans is roughly 20 Hz to 20 kHz (ultrasound lies above it).

An atom has a small dense nucleus of protons and neutrons, surrounded by electrons; the atomic number Z equals the proton count and determines the element.

Mass number A = Z + N (protons + neutrons); isotopes have the same Z but different N, e.g. carbon-12 and carbon-14.

Alpha decay emits a helium nucleus (⁴₂He): A falls by 4 and Z by 2. Beta-minus decay turns a neutron into a proton, so Z rises by 1 and A is unchanged.

Gamma radiation is high-energy electromagnetic radiation emitted by an excited nucleus; it changes neither A nor Z.

Penetration: alpha is stopped by paper or a few centimetres of air; beta by a few millimetres of aluminium; gamma needs thick lead or concrete.

Ionising radiation is detected with a Geiger–Müller counter; half-life is the time for half the nuclei in a sample to decay, and it is not affected by temperature or pressure.

Activity A = ΔN/Δt (becquerel); after n half-lives the remaining fraction is (1/2)ⁿ.

Nuclear fission splits a heavy nucleus and releases energy; nuclear fusion joins light nuclei, powers the Sun, and needs extremely high temperature.

Radiation safety uses the principles of distance, shielding and limiting exposure time; background radiation comes from cosmic rays, radon and rocks.

SI base units include the metre, kilogram, second, ampere, kelvin, mole and candela; derived units such as the newton and joule are built from these.

Prefixes: k = 10³, M = 10⁶, G = 10⁹, m = 10⁻³, μ = 10⁻⁶, n = 10⁻⁹. Convert to base units before calculating.

A hypothesis must be testable; a fair test changes one independent variable while controlling all others and measuring the dependent variable.

Accuracy is closeness to the true value; precision is closeness of repeated readings to each other. Random errors scatter readings; systematic errors shift all readings the same way.

The resolution of an instrument is the smallest change it can show; a ruler with 1 mm divisions is read to about 0.5 mm.

A result is normally reported as mean ± uncertainty, with the same number of decimal places in both parts.

Density ρ = m/V, a useful derived quantity for identifying materials and checking measurement results.

On a graph, the gradient of a straight line is Δy/Δx and the intercept shows the value when the x-axis quantity is zero; anomalous points are noted, not silently deleted.

Energy sources split into renewable (solar, wind, hydro, biomass, geothermal) and non-renewable (coal, oil, gas, nuclear fuel).

Energy is conserved but not all of it is useful: efficiency = useful output energy / total input energy × 100%.

Fossil-fuel power stations convert chemical energy → thermal → kinetic → electrical; waste heat is released to cooling water or the atmosphere.

Wind power depends on the cube of wind speed (P ∝ v³), so siting matters more than small turbine changes.

A domestic appliance's energy use in kWh is power in kW multiplied by hours of use; a 2000 W heater run for 3 h uses 6 kWh.

Household safety: earth/ground wires and residual-current devices protect users; water and mains electricity must be kept apart.

Light-emitting diodes convert a larger fraction of electrical energy into light than filament lamps, which waste most energy as heat.

Noise is measured in decibels (dB) on a logarithmic scale; a 10 dB rise is about ten times the sound intensity.

Radioactive waste and CO₂ emissions are environmental costs that must be compared alongside the benefits when choosing an energy source.

Distance is a scalar (path length); displacement is a vector from start to finish and can be zero.

A distance–time graph's gradient gives speed; a velocity–time graph's gradient gives acceleration and its area gives displacement.

Density ρ = m/V links mass and volume; an object floats when its average density is less than that of the fluid.

Momentum p = mv is conserved in collisions; in an elastic collision kinetic energy is also conserved, in an inelastic one it is not.

Hooke's law F = kx applies up to the elastic limit; the spring constant k is measured in N/m.

Heat flows spontaneously from a hotter body to a colder one until thermal equilibrium is reached.

Absolute temperature must be used in gas-law calculations; doubling T in kelvin at constant volume doubles p.

A vacuum flask reduces conduction and convection (vacuum, stopper) and radiation (silvered surfaces).

Evaporation happens at any temperature below boiling point and cools the remaining liquid; boiling occurs at a fixed temperature for a given pressure.

Pressure of a fixed gas rises with temperature because particles hit the walls more often and harder.

Resistance R = U/I (ohm); for a wire, R increases with length and decreases with cross-sectional area.

Charge is measured in coulombs; 1 A for 1 s transfers 1 C.

An ammeter has very low resistance and is connected in series; a voltmeter has very high resistance and is connected in parallel.

In a series circuit the total voltage equals the sum of the component voltages; in parallel each branch has the full supply voltage.

A transformer changes AC voltage: U1/U2 = N1/N2; it works only with alternating current.

Visible light spans roughly 400 nm (violet) to 700 nm (red); white light splits into a spectrum by a prism because refraction depends on wavelength.

Refractive index n = c/v, where c ≈ 3.0 × 10⁸ m/s in vacuum; n is always at least 1.

Magnification m = image height / object height = b/a for a lens.

Diffraction is the spreading of waves around obstacles; it is noticeable when the obstacle or gap is comparable to the wavelength.

The period T = 1/f is the time for one complete oscillation; amplitude does not affect wave speed.

In a nuclear equation, mass number and atomic number must balance on both sides.

One becquerel is one decay per second; absorbed dose is measured in grays and equivalent dose in sieverts.

Carbon-14 dating works because living things exchange carbon with the environment until they die.

A nucleus is held together by the strong nuclear force, which acts over very short distances and overcomes proton repulsion.

Mass defect: the mass of a nucleus is slightly less than the sum of its separate nucleons; the difference appears as binding energy.

Standard form writes numbers as a × 10ⁿ with 1 ≤ a < 10, which avoids counting zeros in very large or small values.

Percentage difference = |measured − accepted| / accepted × 100%.

Repeat readings and average them to reduce the effect of random errors; systematic errors need calibration or a better method.

A table of results should name each quantity, give its unit in the heading and keep consistent decimal places.

A conclusion must refer back to the hypothesis and be supported by the data, including any outliers.

A car's kinetic energy grows with the square of speed, so braking distance is much longer at high speed.

Seat belts and crumple zones increase the stopping time and distance, reducing the force on occupants (F = Δp/Δt).

Solar panels convert light directly into electrical energy; their output depends on irradiance, angle and shading.

Hydroelectric plants convert gravitational potential energy of stored water into electrical energy via turbines and generators.

Recycling metals saves energy because extracting metal from ore requires far more energy than melting scrap.