MATSEC IM Physics flashcards

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

Newton's second law

The resultant force on a body equals the rate of change of its momentum; for constant mass this reduces to F = ma, with force in newtons.

Conservation of momentum

In a closed system with no external resultant force, total linear momentum before an interaction equals total momentum after it. Momentum is a vector, so direction must be included.

Young modulus

The ratio of tensile stress to tensile strain for a material in its linear region, E = (F/A)/(ΔL/L). It measures stiffness and has units of pascals.

Archimedes' principle

The upthrust on a body immersed in a fluid equals the weight of fluid it displaces. A floating body displaces fluid whose weight equals its own weight.

Centripetal force

The resultant force directed toward the centre of a circular path, of magnitude mv²/r. It is not a new kind of force but is supplied by tension, gravity, friction or similar.

Wave equation

For any progressive wave, speed equals frequency multiplied by wavelength, v = fλ. Frequency is set by the source and does not change when the wave enters a new medium.

Diffraction grating equation

For light of wavelength λ incident normally on a grating with slit spacing d, principal maxima occur at angles given by d sinθ = nλ, where n is the order.

Critical angle

The angle of incidence in the denser medium for which the refracted ray travels along the boundary at 90 degrees. It satisfies sinθc = n₂/n₁.

Simple harmonic motion

Oscillation in which acceleration is proportional to displacement and directed toward the equilibrium position, a = −ω²x. Its period is independent of amplitude.

Snell's law

When light crosses a boundary between two media, n₁ sinθ₁ = n₂ sinθ₂, where angles are measured from the normal and n = c/v for each medium.

Resonance

The large-amplitude response that occurs when a system is driven at its natural frequency. Damping lowers and broadens the resonant peak.

Ohm's law

For an ohmic conductor at constant temperature, current is directly proportional to potential difference, V = IR. The resistance is constant and the V–I graph is a straight line.

Kirchhoff's junction law

The sum of currents entering a junction equals the sum leaving it, expressing conservation of charge. It holds at every instant in any circuit.

EMF and internal resistance

The EMF of a source is the energy it supplies per unit charge. With internal resistance r, terminal voltage is ε − Ir, so it falls as current increases.

Faraday's law of induction

The induced EMF in a circuit equals the rate of change of magnetic flux linkage through it. Faster changes in flux or more turns give larger EMFs.

Capacitor time constant

For a capacitor discharging through a resistor, the time constant τ = RC is the time for the charge to fall to about 37 percent of its initial value.

Fleming's left-hand rule

For a current-carrying conductor in a magnetic field, the first finger points along the field, the second along current, and the thumb along the force.

Specific latent heat

The energy needed to change the state of one kilogram of a substance at constant temperature, Q = mL. It is measured in joules per kilogram.

Ideal gas equation

For n moles of an ideal gas, pV = nRT, where T is absolute temperature and R is 8.31 J mol⁻¹ K⁻¹. It combines the pressure, volume and temperature laws.

First law of thermodynamics

The change in internal energy of a system equals the heat supplied to it minus the work done by it, ΔU = Q − W. It is a statement of energy conservation.

Kinetic theory result

The average translational kinetic energy of a gas molecule is (3/2)kT, depending only on absolute temperature and not on the identity of the gas.

Thermal conduction equation

The rate of heat flow through a slab is kAΔT/L, where k is thermal conductivity, A the cross-sectional area, ΔT the temperature difference and L the thickness.

Photoelectric equation

Light of frequency f ejects electrons from a metal only if hf exceeds the work function φ; the maximum kinetic energy is hf − φ.

de Broglie wavelength

Every particle has an associated wavelength λ = h/p, where p is its momentum. The effect is measurable for electrons and other low-mass particles.

Radioactive decay law

The number of undecayed nuclei falls exponentially, N = N₀e^(−λt), where λ is the decay constant. Half-life equals ln2 divided by λ.

Gravitational field strength

The gravitational force per unit mass at a point, g = GM/r² outside a spherical mass. Near Earth's surface it is about 9.8 N kg⁻¹.

Photon energy

The energy carried by a single photon of frequency f or wavelength λ is E = hf = hc/λ, where h is Planck's constant.

Stationary wave

A wave pattern formed by two identical waves travelling in opposite directions, with fixed nodes of zero displacement and antinodes of maximum displacement. No net energy is transferred.

Polarisation

The restriction of a transverse wave's oscillations to one plane. It is possible for light but not for sound, showing that sound is longitudinal.

Drift velocity

The average velocity of charge carriers along a conductor, related to current by I = nAve. It is typically very small, yet the current appears almost instantly.

Magnetic flux linkage

The product of the number of turns and the magnetic flux through each turn, NΦ = NBA cosθ, measured in webers or weber-turns. It determines induced EMF.

Root-mean-square speed

The square root of the mean of the squared speeds of gas molecules. For an ideal gas v_rms = √(3kT/m), where m is the mass of one molecule.

Energy level transition

When an electron moves between discrete atomic energy levels, a photon is emitted or absorbed with energy hf equal to the difference between the levels.