Physics terms: T

T

Temperaturealso temperatures

A measure of how hot a body is; on the particle model, the kelvin temperature is proportional to the mean random kinetic energy of the particles.

Introduced in B.1 Thermal energy transfers

Temperature gradient

The change in temperature per unit distance through a material, $\Delta T/\Delta x$; measured in $\text{K m}^{-1}$.

Introduced in B.1 Thermal energy transfers

Tensionalso tensions

The pulling force exerted by a stretched string, rope, cable or chain, acting along it and away from the body it is attached to.

Introduced in A.2 Forces and momentum

Terminal potential differencealso terminal pd, terminal voltage

The pd between the terminals of a source, $V = \varepsilon - Ir$; it equals the emf only when no current flows.

Introduced in B.5 Current and circuits

Terminal speedalso terminal velocity, terminal speeds

The constant speed reached by a body falling through a fluid when the upward forces on it balance its weight, so that its acceleration is zero.

Introduced in A.1 Kinematics

Teslaalso T, teslas

The SI unit of magnetic flux density: the field that exerts a force of 1 N on a 1 m length of wire carrying 1 A at right angles to it; $1\ \text{T} = 1\ \text{N A}^{-1}\ \text{m}^{-1}$.

Introduced in D.3 Motion in electromagnetic fields

Test chargealso test charges

A small positive charge used to detect and measure an electric field, small enough not to disturb the charges producing the field.

Introduced in D.2 Electric and magnetic fields

Test massalso test masses

A mass small enough not to disturb the field it is placed in, used to define the field strength or potential at a point.

Introduced in D.1 Gravitational fields

Thermal conductivityalso thermal conductivities

The rate of thermal energy transfer per unit area per unit temperature gradient through a material, $k$ in $\Delta Q/\Delta t = kA\,\Delta T/\Delta x$; measured in $\text{W m}^{-1}\ \text{K}^{-1}$

Thermal energyalso heat

Energy transferred from one body to another because of a temperature difference between them.

Introduced in B.1 Thermal energy transfers

Thermal equilibrium

The state of two bodies between which there is no net transfer of thermal energy, because they are at the same temperature.

Introduced in B.1 Thermal energy transfers

Thermal neutronalso thermal neutrons, slow neutron, slow neutrons

A neutron slowed until its kinetic energy is similar to that of the surrounding particles, about 0.025 eV; it is far more likely than a fast neutron to cause fission of uranium-235.

Introduced in E.4 Fission

Thermal radiation

Electromagnetic radiation, mainly infrared at everyday temperatures, emitted by every body above absolute zero because of the thermal motion of its charged particles.

Introduced in B.1 Thermal energy transfers

Thermal reservoirHL only · also reservoir, hot reservoir, cold reservoir, heat reservoir

A body so large that its temperature does not change noticeably when thermal energy is transferred to or from it.

Introduced in B.4 Thermodynamics

Thermionic emission

The release of electrons from the surface of a heated metal, when some electrons gain enough energy to escape.

Introduced in D.3 Motion in electromagnetic fields

Thermistoralso thermistors, NTC thermistor

A semiconductor resistor whose resistance changes with temperature; the common type's resistance falls as its temperature rises.

Introduced in B.5 Current and circuits

Thinking distancealso reaction distance

The distance a vehicle travels at constant speed during the driver's reaction time: speed × reaction time.

Introduced in A.1 Kinematics

Third-law pairalso third-law pairs, Newton's third law pair, action–reaction pair

Two forces of the same type that two bodies exert on each other, equal in size and opposite in direction, acting on different bodies.

Introduced in A.2 Forces and momentum

Threshold frequencyHL only · also threshold frequencies, cut-off frequency

The minimum frequency of electromagnetic radiation that releases electrons from a given metal surface: $f_0 = \Phi/h$.

Introduced in E.2 Quantum physics

Threshold wavelengthHL only · also threshold wavelengths, cut-off wavelength

The longest wavelength of electromagnetic radiation that releases electrons from a given metal surface: $\lambda_0 = hc/\Phi$.

Introduced in E.2 Quantum physics

Thrustalso rocket thrust

The forward force on a rocket or jet engine from expelling gas backwards, approximately the mass flow rate times the exhaust speed, $(\Delta m/\Delta t)\,v$.

Introduced in A.2 Forces and momentum

Time dilationHL only · also dilated time

The lengthening of a time interval measured by an observer for whom a clock is moving: $\Delta t = \gamma\Delta t_0$, so a moving clock runs slow.

Introduced in A.5 Galilean and special relativity

Time of flightalso flight time

The total time a projectile spends in the air, from launch until it lands.

Introduced in A.1 Kinematics

Timelike intervalHL only · also timelike

A space-time interval with $(\Delta s)^2 > 0$: the events can be linked by a body slower than light, so one can cause the other and all observers agree on their order.

Introduced in A.5 Galilean and special relativity

TorqueHL only · also torques, moment of a force, moment

The turning effect of a force about an axis: the force multiplied by the perpendicular distance from the axis to its line of action, $\tau = Fr\sin\theta$, measured in $\text{N m}$.

Introduced in A.4 Rigid body mechanics

Torsion balancealso Cavendish experiment

An instrument that measures a very small force from the angle through which it twists a rod hanging on a thin wire; Cavendish used one to measure $G$ in 1798.

Introduced in D.1 Gravitational fields

Total internal reflectionalso TIR, totally internally reflected

The complete reflection of a wave at a boundary with a medium in which it would travel faster, when the angle of incidence exceeds the critical angle.

Introduced in C.3 Wave phenomena

Trajectoryalso trajectories, path of a projectile

The path followed by a moving body; for a projectile with no fluid resistance it is a parabola.

Introduced in A.1 Kinematics

TranslationHL only · also translational motion

Motion in which every point of a body moves through the same displacement, without turning.

Introduced in A.4 Rigid body mechanics

Translational equilibriumalso equilibrium of forces

The state of a body on which the resultant force is zero, so that it is at rest or moves with constant velocity.

Introduced in A.2 Forces and momentum

Translational kinetic energyHL only

The kinetic energy of a body due to the motion of its centre of mass, $\tfrac12mv^2$.

Introduced in A.4 Rigid body mechanics

Transmissionalso transmitted

The passage of a wave across a boundary from one medium into another. The frequency is unchanged; the speed and wavelength change in the same ratio.

Introduced in C.3 Wave phenomena

Transverse wavealso transverse waves, transverse

A wave in which the oscillations are perpendicular to the direction of energy transfer.

Introduced in C.2 Wave model

Travelling wavealso travelling waves, progressive wave, progressive waves

A wave whose disturbance moves through a medium or through space, transferring energy without any net transfer of matter.

Introduced in C.2 Wave model

Troughalso troughs

A point of maximum negative displacement on a transverse wave.

Introduced in C.2 Wave model

Tuned mass damperalso tuned mass dampers

A mass on a spring (with damping) attached to a structure and tuned to the structure's natural frequency, so that it oscillates out of phase with the structure and absorbs energy from it.

Introduced in C.1 Simple harmonic motion