Physics: Work, Energy, Circuits, and Magnetic Fields

Vocabulary practice flashcards covering work, kinetic and potential energy, conservation laws, DC circuits, Ohm's law, Kirchhoff's rules, RC circuits, magnetic fields, and electromagnetic forces.

Work Done by a Constant Force

The work done by a constant force acting on an object is equal to the product of the magnitudes of the displacement and the component of the force parallel to that displacement, given by $W = (F \cos(\theta)) s$.

Joule

The SI unit of work and energy, defined as one newton-meter ($1\,\text{N}\cdot\text{m} = 1\,\text{J}$).

Kinetic Energy

The energy of an object due to its motion, defined operationally from kinematics as $K = \frac{1}{2} m v^2$.

Work-Energy Theorem

A theorem stating that the total work done by the net force on a particle equals the change in the particle's kinetic energy: $W_{\text{tot}} = K_2 - K_1 = \Delta K$.

Gravitational Potential Energy

The energy that an object of mass $m$ has by virtue of its position relative to the surface of the earth, measured by height $h$ relative to an arbitrary zero level: $PE = m g h$.

Conservative Force

A force for which the work done on a moving object is independent of the path between the initial and final positions, or equivalently, a force that does zero work on an object moving around a closed path.

Nonconservative Force

A force for which the work done depends on the path taken (such as kinetic friction or air resistance) and for which the concept of potential energy is not defined.

Principle of Conservation of Mechanical Energy

The principle stating that the total mechanical energy ($E = KE + PE$) of an object remains constant as the object moves, provided that the net work done by external nonconservative forces is zero.

Average Power

The rate at which work is done, obtained by dividing the work by the time required to perform the work ($P = \frac{W}{t} = F v$), measured in watts ($1\,\text{W} = 1\,\text{J/s}$) or horsepower ($1\,\text{hp} = 550\,\text{ft}\cdot\text{lb/s} = 745.7\,\text{W}$).

Electromotive Force (emf)

The maximum potential difference across the terminals of a battery or source resulting from the transfer of electrons via chemical reactions.

Electric Current

The rate at which charge flows through a cross-sectional surface, defined as $I = \frac{\Delta q}{\Delta t}$, with the SI unit of ampere ($1\,\text{A} = 1\,\text{C/s}$).

Conventional Current

The hypothetical flow of positive charges from a point of higher potential to a point of lower potential (from the positive to the negative terminal) that has the same effect as the actual movement of negative charges.

Ohm's Law

The principle that the ratio of voltage $V$ applied across a material to the current $I$ through it is constant: $\frac{V}{I} = R = \text{constant}$, or $V = I R$, where $R$ is measured in ohms ($\Omega$).

Resistivity

An intrinsic material property $\rho$ with units of $\Omega\cdot\text{m}$ that relates a specimen's resistance to its geometry via $R = \rho \frac{L}{A}$.

Temperature Coefficient of Resistivity

A parameter $\alpha$ that describes the fractional change in resistivity per degree change in temperature, governed by $\rho = \rho_0 [1 + \alpha (T - T_0)]$.

Electric Power

The average rate at which electrical energy is delivered to an external circuit, given by $P = I V = I^2 R = \frac{V^2}{R}$, with the SI unit of watt ($\text{W}$).

Series Wiring

A circuit arrangement where devices are connected along a single path such that the same electric current flows through each device and total equivalent resistance is $R_S = R_1 + R_2 + R_3 + \dots$.

Parallel Wiring

A circuit arrangement where devices are connected across common points such that the same voltage is applied across each device, with equivalent resistance given by $\frac{1}{R_P} = \frac{1}{R_1} + \frac{1}{R_2} + \dots$.

Internal Resistance

The resistance inherent to a battery or generator that reduces its terminal voltage below the ideal electromotive force when current flows.

Kirchhoff's Junction Rule

A circuit analysis rule based on conservation of charge stating that the sum of the magnitudes of the currents directed into a junction equals the sum of the magnitudes of the currents directed out of the junction.

Kirchhoff's Loop Rule

A circuit analysis rule based on conservation of energy stating that around any closed circuit loop, the sum of all potential drops equals the sum of all potential rises.

DC Galvanometer

A device whose coil of wire and pointer rotate when current passes through the wire, used as the fundamental movement in analog ammeters and voltmeters.

Shunt Resistor

A small resistor placed in parallel with a galvanometer coil to enable it to operate as an ammeter by allowing excess current to bypass the coil.

RC Time Constant

The characteristic time parameter of an $RC$ circuit, given by $\tau = R C$, that governs the exponential rate of capacitor charging and discharging.

Magnetic Field

The region around a magnet or moving charge where magnetic forces act; its magnitude is defined as $B = \frac{F}{|q_0| (v \sin(\theta))}$, measured in tesla ($1\,\text{T} = 1\,\frac{\text{N}\cdot\text{s}}{\text{C}\cdot\text{m}}$) or gauss ($1\,\text{gauss} = 10^{-4}\,\text{T}$).

Angle of Declination

The angle by which a compass needle deviates from geographic north, measured as approximately $12^\circ\,\text{west}$ for New York City.

Right Hand Rule No. 1 (RHR-1)

A directional rule where the fingers point along the magnetic field $\mathbf{B}$, the thumb points along velocity $\mathbf{v}$, and the palm faces the direction of the magnetic force $\mathbf{F}$ acting on a positive charge.

Magnetic Force on a Current-Carrying Wire

The force exerted by a magnetic field on an electric current passing through a wire of length $L$, defined as $F = I L B \sin(\theta)$.

Magnetohydrodynamic (MHD) Propulsion

A propulsion mechanism that uses a superconducting electromagnet and electric current through seawater to generate a magnetic force on the water, driving a water jet out the back to thrust a vessel forward, as demonstrated by the Yamato 1.