Estonian Basic-School Physics Exam flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Average speed

Total distance travelled divided by total time taken, measured in metres per second. It ignores direction, unlike average velocity, which uses displacement and can be zero for a closed round trip.

Newton's second law

The net force on a body equals its mass times its acceleration (F = ma). The acceleration is in the same direction as the net force and is measured in metres per second squared.

Weight versus mass

Mass is the amount of matter in a body, measured in kilograms and unchanged by location. Weight is the gravitational force on it, G = mg, measured in newtons and varying with g.

Hydrostatic pressure

Pressure inside a liquid at rest equals density × gravitational field strength × depth (p = ρgh). It depends only on depth and liquid density, not on the shape or width of the container.

Conservation of mechanical energy

When only gravity and elastic forces do work, the sum of kinetic and potential energy stays constant. Friction converts part of the mechanical energy into thermal energy, so the total mechanical energy falls.

Specific heat capacity

The energy needed to raise the temperature of one kilogram of a substance by one kelvin, in joules per kilogram-kelvin. Water's value of about 4200 J/(kg·K) is unusually large.

Latent heat of fusion

The energy needed to melt one kilogram of a solid at its melting point without changing temperature, in joules per kilogram. The same energy is released when the substance freezes.

Convection

Heat transfer by the bulk movement of a fluid. Warm fluid expands, becomes less dense and rises, while cooler fluid sinks, producing a circulation current; it cannot occur in solids.

Absolute zero

The lowest possible temperature, 0 K or about −273 °C, at which particle motion is minimal. Kelvin temperatures are obtained by adding 273 to the Celsius value.

Boyle's law

For a fixed mass of gas at constant temperature, pressure multiplied by volume is constant (p1V1 = p2V2). Halving the volume therefore doubles the pressure.

Ohm's law

For a metallic conductor at constant temperature, current is proportional to voltage (U = IR). Resistance in ohms equals voltage divided by current; filament lamps do not obey it as they heat.

Series circuit rules

In a series circuit the current is the same through every component, the supply voltage equals the sum of component voltages, and the total resistance is the sum of the individual resistances.

Parallel circuit rules

In a parallel circuit every branch has the full supply voltage, the total current is the sum of branch currents, and total resistance is less than the smallest branch resistance.

Electrical power

The rate at which a component transfers electrical energy, P = UI, also written I²R or U²/R. It is measured in watts; energy used equals power multiplied by time.

Electromagnetic induction

A voltage is induced in a conductor when the magnetic field through it changes, for example when a magnet moves in a coil. Generators use this effect to produce electricity.

Wave equation

Wave speed equals frequency multiplied by wavelength (v = fλ). Frequency is fixed by the source; when a wave enters a new medium, its speed and wavelength change but frequency stays the same.

Law of reflection

The angle of incidence equals the angle of reflection, both measured between the ray and the normal to the surface. The incident ray, reflected ray and normal lie in one plane.

Total internal reflection

Light travelling from a denser to a less dense medium is completely reflected when the angle of incidence exceeds the critical angle. This effect carries light along optical fibres.

Converging lens

A convex lens that brings parallel rays to a focal point. Depending on object distance it forms real inverted images or, for objects closer than the focal length, a virtual magnified one.

Sound as a wave

Sound is a longitudinal mechanical wave: particles oscillate along the direction of travel. It needs a medium, travels about 340 m/s in air, and cannot cross a vacuum.

Atomic number

The number of protons in a nucleus, which determines the chemical element. In a neutral atom it also equals the number of orbiting electrons.

Isotopes

Atoms of the same element with the same proton number but different neutron numbers, so their mass numbers differ. They share chemical properties but may have different nuclear stability.

Alpha particle

A helium nucleus of two protons and two neutrons emitted in alpha decay. It is strongly ionising but stopped by paper or a few centimetres of air.

Beta-minus decay

A neutron in the nucleus turns into a proton, emitting an electron and an antineutrino. The atomic number rises by one while the mass number stays unchanged.

Half-life

The time taken for half the radioactive nuclei in a sample to decay, or for its activity to halve. It is a fixed property of the nuclide, unaffected by temperature or pressure.

SI base units

The seven fundamental units: metre, kilogram, second, ampere, kelvin, mole and candela. Derived units such as newton, joule and watt are combinations of these.

Accuracy versus precision

Accuracy is how close a reading is to the true value; precision is how close repeated readings are to each other. Systematic errors reduce accuracy, random errors reduce precision.

Density

Mass per unit volume, ρ = m/V, measured in kilograms per cubic metre. It is a property of the material and helps identify substances and predict floating or sinking.

Fair test

An experiment in which only the independent variable is changed, the dependent variable is measured, and all other relevant variables are kept constant so the result can be attributed.

Efficiency

Useful energy output divided by total energy input, expressed as a percentage. The remaining energy is transferred to the surroundings, usually as heat, and cannot be fully recovered.

Renewable energy source

An energy source naturally replenished on a human timescale, such as solar, wind, hydro, biomass or geothermal. Fossil fuels and nuclear fuel are non-renewable because reserves are finite.

Kilowatt-hour

A unit of energy equal to one kilowatt of power used for one hour, or 3.6 million joules. Electricity meters record consumption in kilowatt-hours for billing.