BSEH SS Physics flashcards

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

Coulomb's law

The electrostatic force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation, acting along the joining line.

Gauss's law

The total electric flux through any closed surface equals the enclosed charge divided by the permittivity of free space, regardless of the surface shape.

Capacitance in series

For capacitors joined in series the reciprocal of the equivalent capacitance equals the sum of the reciprocals of the individual capacitances, and charge is the same on each.

Electric dipole moment

A vector of magnitude charge times separation, directed from negative to positive charge; the torque on it in a field is pE sinθ.

Drift velocity

The small average velocity along a conductor acquired by free electrons under an applied field; it is typically of order 10⁻⁴ m/s and equals I/(nAe).

Kirchhoff's junction rule

The algebraic sum of currents entering any junction in a circuit is zero, expressing conservation of electric charge at that point.

Wheatstone bridge balance

The bridge is balanced, with no galvanometer deflection, when the ratio of the two known arms equals the ratio of the two unknown arms.

Maximum power transfer

A source of emf with internal resistance delivers maximum power to an external load when the load resistance equals the internal resistance.

Biot–Savart law

The magnetic field due to a current element is proportional to current times element length, inversely proportional to the square of distance, and perpendicular to both.

Cyclotron frequency

A charged particle moving perpendicular to a uniform magnetic field circles with frequency qB/2πm, independent of its speed for non-relativistic motion.

Magnetic dipole moment of loop

For a current loop it equals current times area times number of turns, directed along the axis by the right-hand rule; torque in a field is mB sinθ.

Galvanometer to ammeter

A low resistance shunt placed in parallel with a galvanometer diverts most of the current, converting it into an ammeter of larger range.

Lenz's law

The direction of an induced current is such that it opposes the change in magnetic flux that produced it, a consequence of energy conservation.

Resonance in series LCR

When the inductive and capacitive reactances are equal, impedance is purely resistive and minimum, so current is maximum at angular frequency one over root LC.

Power factor

In an AC circuit it equals the cosine of the phase angle between voltage and current, and also equals resistance divided by impedance.

Transformer principle

Mutual induction between two coils on a common core changes voltage in the ratio of turns; an ideal transformer conserves power, so current changes inversely with voltage.

Displacement current

A changing electric flux produces an effective current equal to permittivity times the rate of change of flux, which generates a magnetic field like a conduction current.

Electromagnetic wave speed

In vacuum electromagnetic waves travel at the reciprocal square root of the product of permeability and permittivity of free space, about 3×10⁸ m/s.

Radiation pressure

Electromagnetic radiation carries momentum, exerting pressure equal to intensity divided by the speed of light on a perfectly absorbing surface, twice that if fully reflected.

Snell's law

At an interface the product of refractive index and sine of the angle with the normal is constant, so light bends toward the normal entering a denser medium.

Critical angle

The angle of incidence in the denser medium for which the refracted ray grazes the interface; its sine equals the reciprocal of the refractive index.

Fringe width in double slit

The separation between consecutive bright fringes equals wavelength times screen distance divided by slit separation, and is proportional to wavelength.

Brewster's law

At the polarising angle of incidence, the reflected ray is completely polarised, and the tangent of that angle equals the refractive index of the medium.

Photoelectric equation

The maximum kinetic energy of an emitted electron equals the photon energy minus the work function, so it depends on frequency but not on intensity.

de Broglie wavelength

Every moving particle has an associated wavelength equal to Planck's constant divided by its momentum, verified for electrons by diffraction experiments.

Stopping potential

The reverse voltage that just prevents the fastest photoelectrons from reaching the collector; it measures their maximum kinetic energy in electron-volts.

Bohr energy levels

In the Bohr model the energy of the nth orbit of hydrogen is negative 13.6 electron-volts divided by n squared, the ground state being lowest.

Half-life

The time in which half the radioactive nuclei in a sample decay; it equals the natural logarithm of two divided by the decay constant.

Binding energy per nucleon

The total nuclear binding energy divided by mass number; it peaks near iron, so both fusion of light and fission of heavy nuclei release energy.

Depletion region

The charge-depleted zone around a p–n junction containing fixed ions, which creates a barrier potential opposing further diffusion of carriers.

Zener diode regulation

Operated in reverse breakdown, a Zener diode holds a nearly constant voltage across it, so it can stabilise the output of a supply.

Transistor current gain beta

In a transistor, beta equals collector current divided by base current, and relates to alpha by beta equals alpha divided by one minus alpha.