OpenStem

@openstem · Joined Jul 2026

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Flashcards9 cards

What does a converging (convex) lens do to parallel light rays passing through it, and where do they end up?1 / 9

It refracts the rays inward so that all of them meet at a single point on the far side of the lens — the focal point. The distance from the lens to this point is the focal length, f.

Physics

Physics · L3 · Lenses & Optical Instruments

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Flashcards10 cards

As an ambulance drives toward you with its siren blaring, then passes and speeds away, what do you notice about the pitch of the siren?1 / 10

The pitch sounds higher than normal while it approaches, then drops noticeably lower the instant it passes and starts moving away. This is the Doppler effect — the siren's own emitted frequency never changes; only what you hear changes, because of the relative motion between you and the source.

Physics

Physics · L3 · The Doppler Effect

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Flashcards8 cards

State Newton's Third Law.1 / 8

For every action force, there is a reaction force equal in size and opposite in direction, acting on a different object.

Physics

Physics · L3 · Newton's Third Law

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Flashcards8 cards

What do the letters in "SUVAT" stand for?1 / 8

s = displacement, u = initial velocity, v = final velocity, a = acceleration, t = time. The SUVAT equations connect these five quantities for motion at constant acceleration.

Physics

Physics · L3 · 1D Kinematics: The SUVAT Equations

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Flashcards9 cards

What does this equation define?1 / 9

Electric potential (voltage) — the electric potential energy U per unit of charge q at a point.

Physics

Physics · L3 · Electric Potential & Capacitors

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What does this equation calculate?1 / 8

The magnetic force on a current-carrying wire of length L, in a magnetic field of strength B, where θ is the angle between the wire and the field.

Physics

Physics · L3 · Magnetic Force on Current-Carrying Wires

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Flashcards8 cards

State the First Law of Thermodynamics.1 / 8

Energy cannot be created or destroyed, only converted from one form to another or transferred as heat and work. The total energy of an isolated system stays constant.

Physics

Physics · L3 · The Laws of Thermodynamics & Heat Engines

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Flashcards8 cards

What does this equation, the continuity equation, describe?1 / 8

For a fluid flowing through a pipe, the cross-sectional area (A) times the flow speed (v) stays constant — so where the pipe narrows, the fluid speeds up.

Physics

Physics · L3 · Fluid Dynamics: Continuity & Bernoulli's Principle

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Flashcards8 cards

What is electromagnetic induction?1 / 8

The process by which a changing magnetic field through a loop of wire creates (induces) an electric current in that wire.

Physics

Physics · L3 · Electromagnetic Induction: Faraday's & Lenz's Laws

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Flashcards8 cards

What is a standing wave?1 / 8

A wave pattern formed when two identical waves travel in opposite directions and interfere, creating a pattern that appears to stay in place, alternating between fixed peaks and fixed still points.

Physics

Physics · L3 · Standing Waves & Resonance

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Flashcards12 cards

What are the four kinematic equations for constant acceleration?1 / 12

v = v₀ + at; x = x₀ + v₀t + ½at²; v² = v₀² + 2a(x − x₀); x = x₀ + ½(v₀ + v)t. They relate displacement, velocity, acceleration, and time when a is constant.

Physics

Physics · L4 · Kinematics — Motion in 1D & 2D

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Flashcards10 cards

Distinguish elastic from inelastic collisions.1 / 10

Elastic: both momentum AND kinetic energy conserved (e.g. ideal billiard balls, atomic collisions). Inelastic: momentum conserved, KE NOT conserved (some converts to heat/sound). Perfectly inelastic: objects stick together.

Physics

Physics · L4 · Energy, Work & Momentum

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Flashcards11 cards

State Coulomb's law.1 / 11

F = k|q₁q₂|/r², where k = 1/(4πε₀) ≈ 8.99 × 10⁹ N·m²/C². Force is along the line joining the charges: attractive for opposite charges, repulsive for like charges.

Physics

Physics · L4 · Electrostatics — Charge, Field & Potential

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Flashcards10 cards

What is the wave equation relating speed, frequency, and wavelength?1 / 10

v = fλ. Speed v is a property of the medium (not frequency). In vacuum, electromagnetic waves travel at c = 3 × 10⁸ m/s. Angular frequency ω = 2πf; wave number k = 2π/λ; then v = ω/k.

Physics

Physics · L4 · Waves & Optics — Core Concepts

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Flashcards12 cards

Define torque as a vector. How is its magnitude computed?1 / 12

Torque is

Physics

Physics · L4 · Rotational Dynamics

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A 2.0 kg point mass sits 0.50 m from a pivot. A tangential force of 6.0 N is applied at that point, perpendicular to the arm. Find the torque and the resulting angular acceleration.1 / 8

τ = rF sin 90° = (0.50 m)(6.0 N) = 3.0 N·m. I = mr² = (2.0 kg)(0.50 m)² = 0.50 kg·m². From τ = Iα: α = τ/I = 3.0/0.50 = 6.0 rad/s².

Physics

Physics · L4 · Rotational Dynamics

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Flashcards12 cards

State Bernoulli's equation for flow along a streamline.1 / 12

P + ½ρv² + ρgh = constant along a streamline, for steady, incompressible, non-viscous flow. It is a statement of energy conservation per unit volume: pressure energy, kinetic energy, and gravitational potential energy trade off against each other.

Physics

Physics · L4 · Fluid Mechanics

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Flashcards10 cards

State the hydrostatic pressure equation for a fluid at rest.1 / 10

P = P₀ + ρgh, where P₀ is the pressure at the surface (often atmospheric), ρ is fluid density, and h is depth below the surface. Pressure increases linearly with depth and does not depend on the container's shape.

Physics

Physics · L4 · Fluid Mechanics

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Flashcards14 cards

Write the general solution for simple harmonic motion, x(t).1 / 14

x(t) = A·cos(ωt + φ), where A is the amplitude, ω is the angular frequency, and φ is the phase constant set by initial conditions.

Physics

Physics · L4 · Oscillations & Resonance

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Flashcards8 cards

A 0.50 kg mass on a spring with k = 200 N/m starts at rest, displaced 0.10 m. Find ω and T.1 / 8

ω = √(k/m) = √(200/0.50) = √400 = 20 rad/s. T = 2π/ω = 2π/20 ≈ 0.314 s.

Physics

Physics · L4 · Oscillations & Resonance

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Flashcards12 cards

What is magnetic flux, and how is it calculated?1 / 12

Magnetic flux through a loop is

Physics

Physics · L4 · Electromagnetic Induction

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Flashcards12 cards

How does an AC voltage source differ from a DC source?1 / 12

A DC source holds a constant polarity and magnitude. An AC source oscillates sinusoidally: v(t) = V₀ sin(ωt), where V₀ is the peak voltage and ω = 2πf is the angular frequency. Polarity and current direction reverse every half-cycle.

Physics

Physics · L4 · AC Circuits

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Flashcards11 cards

State the thin lens equation and define each term.1 / 11

1/f = 1/d_o + 1/d_i. f is the focal length, d_o is the object distance from the lens, and d_i is the image distance from the lens (all measured along the optical axis, same units).

Physics

Physics · L4 · Geometric Optics — Lenses & Ray Diagrams

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Flashcards8 cards

State the mirror equation and how it relates to the thin lens equation.1 / 8

1/f = 1/d_o + 1/d_i — the exact same form as the thin lens equation. For a spherical mirror, f = R/2, where R is the mirror's radius of curvature.

Physics

Physics · L4 · Geometric Optics — Mirrors & Image Formation

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Flashcards10 cards

What is the entropy change of a system undergoing a reversible process?1 / 10

ΔS = Q_rev/T for an isothermal reversible process, or ΔS = ∫dQ_rev/T in general. Entropy is a state function, so ΔS depends only on the initial and final states, not on the path — even for an irreversible process, you can compute ΔS by inventing a reversible path between the same endpoints.

Physics

Physics · L4 · Entropy & Heat Engines

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Flashcards10 cards

List the four steps of the Carnot cycle in order.1 / 10

1) Isothermal expansion at T_h, absorbing Q_h. 2) Adiabatic expansion, T falls from T_h to T_c (Q = 0). 3) Isothermal compression at T_c, rejecting Q_c. 4) Adiabatic compression, T rises back from T_c to T_h (Q = 0), returning the gas to its starting state.

Physics

Physics · L4 · Entropy & Heat Engines — Carnot Efficiency & Refrigerators

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Flashcards10 cards

What is emitted in alpha decay, and how does it change the nucleus?1 / 10

An alpha particle — a ⁴He nucleus (2 protons + 2 neutrons). The parent's atomic number Z decreases by 2 and mass number A decreases by 4: ᴬZX → ᴬ⁻⁴Z₋₂Y + α.

Physics

Physics · L4 · Nuclear Physics

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Flashcards10 cards

Define binding energy per nucleon and what it measures.1 / 10

BE/A = [Zmₚ + Nmₙ − M(nucleus)]c² / A — the average energy needed to remove one nucleon from the nucleus. Higher BE/A means a more tightly bound, more stable nucleus.

Physics

Physics · L4 · Nuclear Physics

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Flashcards12 cards

State Gauss's law for electricity, and what it says physically.1 / 12

∮ E · dA = Q_enc/ε₀. The total electric flux through any closed surface is proportional to the enclosed charge. Physically: electric field lines start on positive charges and end on negative charges — charge is the source of E.

Physics

Physics · L4 · Maxwell's Equations

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Flashcards8 cards

Write the wave equation Maxwell's equations produce for the electric field in vacuum.1 / 8

∂²E/∂x² = μ₀ε₀ ∂²E/∂t², a standard 1D wave equation with solution speed v = 1/√(μ₀ε₀) = c. An identical equation holds for B. Any function of the form f(x − ct) or f(x + ct) satisfies it.

Physics

Physics · L4 · Maxwell's Equations — EM Wave Properties

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