MTEL Physics (69) flashcards

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

Newton's second law

The net force on an object equals its mass times its acceleration (ΣF = ma). The acceleration points along the net force and is zero when the forces balance.

Centripetal acceleration

An object moving in a circle of radius r at speed v has acceleration v²/r directed toward the center. It changes the direction of velocity, not its magnitude.

Conservation of momentum

If the net external force on a system is zero, total momentum p = mv remains constant. This is why colliding objects obey m₁v₁ + m₂v₂ = m₁v₁′ + m₂v₂′.

Work-energy theorem

The net work done on an object equals its change in kinetic energy: W_net = ½mv_f² − ½mv_i², where each force contributes W = Fd cos θ.

Buoyant force

Archimedes' principle: a submerged or floating object feels an upward force equal to the weight of the displaced fluid, F = ρ_fluid × V_submerged × g.

Simple harmonic motion period

For a mass on an ideal spring, T = 2π√(m/k), depending only on mass and spring constant, not amplitude. A small-angle pendulum has T = 2π√(L/g).

Hooke's law

An ideal spring exerts a restoring force proportional to its displacement and opposite in direction: F = −kx, where k is the spring constant in newtons per meter.

Elastic versus inelastic collisions

Elastic collisions conserve both momentum and kinetic energy. Perfectly inelastic collisions conserve momentum only: the bodies stick together and kinetic energy is lost to other forms.

Wave speed equation

For any periodic wave, speed equals frequency times wavelength: v = fλ. The source determines frequency, while the medium determines the speed.

Snell's law

Refraction at an interface obeys n₁ sin θ₁ = n₂ sin θ₂, where n = c/v is the index of refraction and angles are measured from the normal.

Total internal reflection

Light going from a higher to a lower index bends away from the normal and reflects completely once the incidence angle exceeds θ_c, given by sin θ_c = n₂/n₁.

Thin lens equation

1/f = 1/d_o + 1/d_i with magnification m = −d_i/d_o. A positive image distance corresponds to a real image formed on the far side of the lens.

First law of thermodynamics

The change in internal energy equals heat added minus work done by the system: ΔU = Q − W. For a monatomic ideal gas, U = (3/2)nRT.

Carnot efficiency limit

No heat engine operating between reservoirs at T_H and T_C can exceed e = 1 − T_C/T_H, with both temperatures measured on the kelvin scale.

Latent heat

Energy absorbed or released during a phase change, with no change in temperature, is Q = mL, where L is the latent heat of fusion or vaporization.

Standing waves on a string

A string fixed at both ends supports wavelengths λ = 2L/n and frequencies f = nv/(2L), producing a harmonic series built on the fundamental frequency.

Coulomb's law

The electrostatic force between two point charges is F = kq₁q₂/r² with k ≈ 8.99 × 10⁹ N·m²/C². It is repulsive for like charges and attractive for opposite charges.

Electric field of a point charge

E = kq/r², directed radially outward from positive charge and inward toward negative charge. The force on a test charge is then simply F = qE.

Capacitors in series and parallel

Parallel capacitors add directly (C_eq = C₁ + C₂). In series the reciprocals add, so the equivalent capacitance is smaller than any individual capacitor in the chain.

Ohm's law

For a resistor at constant temperature, current is proportional to voltage: V = IR, with V in volts, I in amperes, and R in ohms.

Electric power dissipation

Power converted in a resistor is P = IV = I²R = V²/R. The I²R form shows that doubling the current quadruples the heating rate in wires.

Kirchhoff's loop rule

Around any closed circuit loop, the algebraic sum of potential differences is zero. This rule is a statement of energy conservation for moving charges.

Magnetic force on moving charge

F = qvB sin θ, directed perpendicular to both the velocity and the magnetic field. A charge moving parallel or antiparallel to B experiences no magnetic force.

Faraday's law of induction

An emf is induced equal to the negative rate of change of magnetic flux: ε = −N ΔΦ/Δt. Lenz's law fixes the direction so the induced current opposes the change.

Photoelectric effect

Light ejects electrons only above a threshold frequency. Maximum kinetic energy is K = hf − φ, set by photon energy and work function, not by intensity.

Photon energy

A photon carries E = hf = hc/λ. Since hc ≈ 1240 eV·nm, a 620 nm visible photon has an energy of roughly 2 eV.

de Broglie wavelength

Any particle with momentum p has an associated wavelength λ = h/p. The wave nature becomes observable only when momentum is extremely small, as for electrons.

Bohr hydrogen energy levels

Hydrogen levels follow E_n = −13.6 eV/n². A transition between levels emits or absorbs a photon whose energy equals the difference between them.

Radioactive half-life

The time for half the nuclei in a sample to decay. Decay obeys N = N₀e^(−λt), and the half-life is T½ = ln2/λ ≈ 0.693/λ.

Mass-energy equivalence

Mass and energy are interchangeable through E = mc². One atomic mass unit corresponds to 931.5 MeV, the scale used for nuclear binding energies.

Alpha decay

A nucleus emits a helium-4 nucleus, reducing mass number A by 4 and atomic number Z by 2. Alpha particles ionize strongly but penetrate matter poorly.

Relativistic time dilation

A moving clock runs slow relative to the observer: Δt = γΔt₀, where γ = 1/√(1 − v²/c²) and Δt₀ is the proper time between events.