Absolute temperature scales are based on thermodynamic principles rather than the physical properties of particular substances. The zero point of such scales is the temperature at which the pressure of an ideal gas would be zero (0 K or −273 °C).
Absolute zero is the lowest possible temperature: −273 °C. At this temperature all particles stop moving, and gases exert no pressure at all.
An object's acceleration is its rate of change of velocity.
Air resistance is the name given to the frictional forces caused by the air in contact with the surface of a moving object.
An alpha particle is a helium nucleus containing 2 protons and 2 neutrons.
An amorphous solid is one in which the atoms or molecules are not organized in a definite crystalline structure.
The ampere is the base unit of electrical current.The precise definition of 1 ampere is stated in terms of the magnetic effect of a current passing through a conductor; however, as a working definition we can say that there is a current of 1 ampere in a circuit when 1 coulomb of charge passes any point in 1 second.
The amplitude of a wave is the distance between the peak of the crest and the undisturbed position.
An analogue signal is composed of a continuous range of values. This is in contrast to a digital signal which is made up of discrete units.
The angle of incidence is the angle between the incident ray and the normal.
The angle of reflection is the angle between the reflected ray and the normal
The angular acceleration of a rotating object is a measurement of the rate of change of its angular velocity. Angular accelerations have units of rads-2.
The angular displacement is the angle through which an object is turned in a specified direction and about a specified axis.
The angular momentum of a rotating body is the product of its moment of inertia and its angular velocity.
The angular velocity ω of a rotating object specifies its rate of rotation. Angular velocities can be measured in radians per second.
Antinodes are the positions of maximum amplitude in a standing wave.
Two parts of an oscillation are in antiphase when the phase difference between them is 180°.
The arc length is the distance along the perimeter between two points on the circumference of a circle.
Archimedes' principle states that, when any object is submerged in a liquid, it experiences an upthrust equal to the weight of liquid displaced.
The atomic number specifies the number of protons in an atom.
Balanced forces occur in situations where the magnitude of the forces acting in opposing directions is the same.
The bandwidth of a signal is a measurement of the range of different frequencies composing the signal.
Bearings are a method of stating direction by measuring the angle, clockwise, from due north.
A beta particle is a fast moving electron.
Binary numbers and signals are made up entirely of strings of 'ons' and 'offs'. These states are usually represented using 1 and 0.
Body-centred cubic means that the atoms of a crystal form a cubic lattice with atoms at the centre of the lattice as well as its corners.
The Boltzmann constant k is a fundamental constant obtained by dividing the molar gas constant by the Avogadro constant. Its value is k = 1.38 JK−1.
Boyle's Law states that the volume of a fixed mass of gas at constant temperature is inversely proportional to the pressure.
A brittle material breaks when the material is extended only a short distance beyond its elastic limit.
The buoyancy force on a submerged object is the upward force exerted upon it by the fluid in which it is immersed. It is also known as the upthrust.
The capacitance of a system is a measurement of its ability to store charge. Numerically the capacitance is equal to the charge stored per volt.
A capacitor is a system of closely spaced conductors designed to store charge. The larger the p.d. across the capacitor plates the more charge stored
An object's centre of gravity is the single point through which the object's weight can be considered to act.
The term centrifugal force is used to explain the apparent outwards for experienced in circular motion.
The centripetal acceleration of an object moving at a constant speed in a circle is a measurement of its rate of change of velocity.
The centripetal force in circular motion is the force needed to produce a centripetal acceleration. The centripetal force is directed towards the centre of the circle.
Clipping occurs when the output from an amplifier becomes saturated.
In a closed packed arrangement of atoms one layer lies directly above the holes in the layer beneath.
The coefficient of friction describes the relationship between the limiting frictional force and the reaction force between surfaces in contact
A comparator is a circuit whose output indicates which one of its two inputs is higher.
The principle of conservation of momentum states that in the absence of external forces the total momentum before bodies interact is equal to the total momentum after their interaction.
The coulomb is the unit of charge. One coulomb is approximately equivalent to the charge carried by 6.25 × 1018 electrons.
A pair of equal-sized turning forces acting in different directions is called a couple.
A material creeps when the extension produced by a constant pulling force increases with time.
The critical angle for a material is the angle in the material for which the refracted angle in the surrounding air is 90°.
The critical mass is the minimum amount of a radioactive substance required before a chain reaction will start.
The rate of flow of charge past any specific point in a circuit. The base unit of current is the Ampere.
DAC is the common abbreviation for digital-to-analogue converter.
Damping is the reduction in amplitude of an oscillating system caused by loss of energy from the system (e.g. by friction). Sometimes the word is also used to refer to the cause of the energy loss.
The deceleration of an objects is a measurement of its rate of change of velocity as it slows down.
A dielectric is a material that is a poor conductor of electricity which can be placed between the plates of a capacitor to increase the energy stored.
In a difference amplifier, the size of the output voltage is determined by the difference between the two input voltages.
A digital signal is recorded in discrete units, often in binary. This is in contrast to an analogue signal which is composed of a continuous range of values.
A diode is an electronic component that only allows an electric current to pass in one direction.
An object's displacement quotes both its bearing and distances relative to a fixed reference point.
Distortion reduces the quality of the output signal from an amplifier. This often occurs when an amplifier reaches saturation.
The dominant frequency is also known as the fundamental frequency. This is the lowest frequency present in any musical note or sound.
Drag, like air resistance, is the name given to the frictional forces caused by the air in contact with the surface of a moving object.
The speed with which electrons move through a material when a p.d. is applied across the material is called the drift velocity.
The drift velocity through a material can be calculated using the formula:
A ductile material extends beyond its elastic limit for some distance before it breaks.
The efficiency of a system is a measurement of the ratio of the useful output power to the total input power.
Collisions where both kinetic energy and momentum are conserved.
The electrical power dissipated by a component is the energy transferred per second when a current passes through the component.
Electromagnetic waves, such as light, are made up from oscillating electric and magnetic fields. Because of this, they are self-propagating and can travel through a vacuum. All types of electromagnetic wave travel at the same speed in a vacuum, 3 × 108 ms−1.
The electromotive force (often abbreviated to EMF) of a battery is a measurement of its capacity to provide energy to the charges.
EMF is the common abbreviation for the electromotive force a measurement of a battery's capacity to provide energy to the charges.
A system has energy when it has the capacity to do work. The scientific unit of energy is the joule.
An exponential variation can be described by a special type of mathematical function. The decrease in the p.d. across a discharging
capacitor is described by this mathematical function:
All the components connected across the terminals of a battery or power supply are collectively known as the external circuit.
Face-centred cubic means that the atoms of a crystal form a cubic lattice with atoms at the centres of the faces of the lattice as well as its corners.
Feedback is when the output signal from a system becomes incorporated into the input signal of the same system.
The focal length of a lens is the distance between the centre of the lens and the principal focus.
The focal point for a convex lens is the point of convergence of all rays parallel to the principal axis.
A focus is a point of convergence of different rays.
Whether the forces acting as an object moves in a circle act inwards or outwards depends upon the position of the observer relative to the motion. This is called a frame of reference.
The wave frequency f is the number of complete waves passing any point each second. Frequency is measured in hertz, Hz.
Friction is a force which acts in a direction opposite to that in which an object is moving.
The fundamental frequency of any musical note or sound is the lowest frequency present.
The fundamental frequency is the lowest possible frequency of standing wave that can be produced in a pipe or on a plucked cord. It is sometimes called the first harmonic. In musical instruments, it is usually the frequency that determines the pitch of a note.
The gain of an amplifier is defined as the output voltage divided by the input voltage.
A satellite is said to be geostationary if it orbits above the equator with a period of one day.
The gravitational field strength is a measurement of the force that a particular planet exerts on a mass of 1kg held near the surface of the planet.
A harmonic tone has a frequency which is an integer multiple of the fundamental frequency.
The frequencies at which a plucked cord or a pipe can resonate are called harmonics. They are integral multiples of the fundamental frequency (which is sometimes known as the first harmonic).
Hooke's law states that the extension produced in a material is directly proportional to the applied force.
An ideal gas is one that obeys Boyle's Law at all pressures.
The impulse of a force is defined as the magnitude of the force multiplied by the length of time the force acts.
Collisions where momentum is conserved but kinetic energy is not.
An object's inertia gives an indication of it reluctance to change its state of motion. Objects with large masses have high inertia.
Infrared radiation is electromagnetic radiation in the wavelength range 700 nm to 1 mm. It is produced by hot objects.
An integrated circuit is a circuit in which all the components are together on the same semiconductor base.
The intensity at a particular point is described as the power per unit area.
All batteries or power supplies have internal resistance. This resistance has the effect of reducing the output p.d. as the current supplied increases.
In an inverting amplifier, the input and output voltages have different polarities.
ionisation occurs when an atom becomes loses or gains one or more electrons. The atom will no longer be electrically neutral, but will have an overall charge.
An oscillation where the periodic time is constant is said to be isochronous.
Isotopes of an element have the same atomic number of different mass numbers.
The joule is the unit of energy.
The kinetic energy of a system is a measurement of the energy associated with its translational motion.
The sum of the currents entering a junction in a circuit is always equal to the sum of the currents leaving it.
Where heat transfers change in the bonding structure of a material without a change in temperature the energy involved is called latent heat.
A lattice is a regular geometric arrangement of points in space. The word is often used of the regular arrangement of atoms in a crystalline solid.
The resistance of a light dependent resistor reduces as the light intensity increases. This feature makes LDRs ideal for use in light sensing circuits.
LED is the common abbreviation for a light emitting diode. When electrons and holes in an LED recombine, the excess energy produced is radiated as photons of light of one particular colour.
The loading effect occurs when a power supply delivers current. The act of delivering current reduces the p.d. available to the load.
A wave is said to be longitudinal when it causes the particles of the medium through which it passes to move parallel to the direction in which the wave is moving.
The luminosity of a light source is defined as the rate at which it radiates energy. In other words, the luminosity is the total energy radiated per second.
The mass number of an atom is the total number of protons and neutrons in the atom's nucleus.
The mechanical advantage is the ratio of the output force of a machine to the input force.
The temperature at which the liquid solidifies if the liquid form is cooled or the temperature at which it melts if its solid form is warmed
A microchip is a very small integrated circuit that may contain many components such as transistors or resistors.
Microwaves are electromagnetic waves with wavelengths in the range 1 mm to 0.1 m.
The molar gas constant is the constant R in the Universal Gas Law, . It is a universal constant for ideal and nearly ideal gases. Its value is R = 8.31 JK−1mol−1.
The turning effect of a single force about a point is called the moment. The size of a moment is defined as the force × the perpendicular distance from the pivot.
An object's moment of inertia is the ratio of its torque to is angular acceleration. Moments of inertia have units of kgm2.
The momentum of a moving object is the product of its mass and velocity.
A monochromatic source of light has one single wavelength.
A type of semiconductor where electrons are the majority charge carriers.
When an oscillating system is allowed to vibrate freely, it tends to do so at a characteristic frequency determined by certain parameters of the system itself (e.g. the mass and spring constant of a loaded spring). This frequency is known as the natural frequency.
Negative feedback in a system is used to ensure that the output signal is as stable as possible.
Nodes are the positions of zero amplitude in a standing wave.
In a non inverting amplifier, the input and output voltages have the same polarity.
The normal to a surface at a given point is a line drawn at right angles to the surface at that point.
Nuclear energy is released by breaking apart or smashing together atoms. This is the energy which powers the sun.
Nuclear fission occurs when a large unstable atom breaks apart via radioactive decay into smaller atoms and nuclear radiation. For example, uranium-235 is unstable and undergoes nuclear fission.
Nuclear fusion occurs when two small atoms are squeezed together to form a heavier atom. For example, in stars, hydrogen atoms undergo nuclear fusion and helium is created.
Ohm's Law states that at constant temperature the current in a conductor is directly proportional to the d.p. across the conductor. The constant of proportionality is called the resistance of the sample.
Op-amp is the common abbreviation for operational amplifier. Op-amps are integrated circuits that were designed to perform mathematical operations such as multiplication, division, addition, subtraction, and even differentiation and integration.
The overtones are the harmonics (excluding the fundamental frequency) produced by a musical instrument. Their relative proportions determine the timbre or quality of the note.
A p-n junction is formed when p-type and n-type semiconductors are placed together. A p-n junction conducts only when forward biased and then only when the applied p.d. is greater than the p.d. across the depletion layer in the junction.
A type of semiconductor where holes are the majority charge carriers.
Components connected in parallel offer alternative paths for charges from a supply.
The pascal is a unit of pressure. 1 Pa is numerically the same as a pressure of 1 N acting on an area of 1 m2.
The periodic time is the time for one repetition of an oscillation
The phase difference between two waves describes how the motion of particles in one wave compares with their motion in the other wave at any particular instant.
Waves vibrating in just one plane are described as plane polarized.
A polycrystalline material is made up of tiny crystals packed together in an irregular manner.
The power of system is a measurement of the rate at which energy is transferred from one form to another. The scientific unit of power is the watt.
Pressure is defined as the force acting on unit area.
The Pressure Law states that for an ideal gas, the pressure P exerted by a fixed mass of gas whose volume is kept constant is directly proportional to the absolute temperature Tk.
The principal axis in a ray diagram is a construction line through the centre of a lens and perpendicular to the lens itself.
The principal focus for a convex lens is the point of convergence of all rays parallel to the principal axis.
Root mean square is often abbreviated to r.m.s. The r.m.s. value of an a.c. signal is the voltage of an equivalent d.c. signal that provides the same amount of energy.
One radian is the specific angle at the centre of a circle required to make the arc length the same as the circle's radius. Equates to an angle of 57.3°
Reactance is the opposition to the flow of charge in an a.c. circuit. Like resistance, it is measured in units of ohms.
The refractive index for a material is the numerical value of the ratio of the sines of the incident and refracted angles.
The velocity of a moving object as viewed from a stationary or moving point is called the relative velocity.
The opposition to the flow of current provided by a circuit is called resistance. Resistance is measured in units called Ohms.
Resistivity is a material property and is numerically the same as the resistance between opposite faces of cube of the material of side 1m.
Resonance occurs when a vibrating system is driven at its natural frequency by an external source of energy. When this happens the amplitude of the system rapidly reaches its maximum possible value.
The resultant of two or more vector quantities is a measurement their overall effect.
A retardation is another way of stating that an object is decelerating or slowing down.
The root mean square value of an a.c. signal is the voltage of an equivalent d.c. signal that provides the same amount of energy. This is often abbreviated to the r.m.s. value.
A rotating object has kinetic energy even though there is no translational motion. This energy is called the rotational energy.
Saturation occurs where changes in the input voltage are not mirrored in the output signal. Saturation will happen if the calculated output voltage is greater than the op-amp's power supply voltage.
A scalar quantity is specified fully by quoting its magnitude alone.
The region of a circle bounded by an arc and the two radii joining its end points to the centre.
Sensors used in electronics produce a change in their resistance when some feature of their surrounding environment changes. The resistance of a thermistor changes as the surrounding temperature alters.
Components are connected in series when the same electrical charges pass through both.
SHM is short for simple harmonic motion motion in which the acceleration is directly proportional to the displacement and the restoring force acts towards the equilibrium position.
A short circuit is when there is a path of zero resistance between two points in a circuit.
An oscillation is described as simple harmonic if its acceleration is directly proportional to its displacement and the restoring force acts towards the equilibrium position.
Sinusoidal variations are continuous changes over time which, when plotted on a graph, have the shape of a sine curve.
Snell's Law states that the ratio of the sines of the incident and refracted angles in a transparent material is a constant.
The quantity of heat involved when 1 kg of a solid at its melting point changes into a liquid at the same temperature
The specific latent heat of vaporisation, L, is the energy needed to turn 1 kg of a material at its boiling point into vapour.
A square wave is a periodic wave that alternates between two different fixed values for equal amounts of time.
The strain ε produced by a particular force is defined as the ratio of the extension to the original length.
The stress σ produced in a material by a stretching force is defined as the force per unit area.
In a summing amplifier, the output voltage is equal to the sum of the individual inputs.
A material through which current can flow without experiencing any resistance is called a superconductor. Certain materials cooled below their transition temperature behave as superconductors.
The tangential speed of an object is a measurement of the actual speed at which a point is moving. Tangential speeds are measured in ms-1.
The terminal p.d. is the voltage available at the terminals of a battery or power supply. The terminal p.d. varies depending on how much current is being drawn.
The terminal velocity of a falling object is the speed at which the forces acting are balanced.
A thermistor is an electronic component whose resistance changes when its temperature alters. The resistance of a 'negative temperature coefficient' (n.t.c.) thermistor reduces as the temperature increases.
Thrust is the name given to the force propelling an object in a specific direction.
The time constant T for a circuit is calculated by multiplying the resistance R and capacitance C values for the circuit: T = RC
The torque of a force is a measurement of the turning effect of the force. Mathematically the torque is the product of the force and its perpendicular distance from the axle. Torques have units of Nm.
A transistor is a semiconductor device that is used extensively in amplifier and switching circuits.
A wave is said to be transverse when it causes the particles of the medium through which it passes to move at right-angles to the direction in which the wave is moving.
Ultraviolet radiation is electromagnetic radiation in the wavelength range 13 nm to 380 nm.
Unbalanced forces occur in situations where the force acting in one direction is greater than the force acting in the opposite direction.
The Universal Gas Law combines Boyle's Law, Charles's Law, and the Pressure Law to give .
The upthrust on a submerged object is the upward force exerted upon it by the fluid in which it is immersed. It is also known as the buoyancy force.
A vector quantity is specified fully only when its magnitude and direction are both quoted.
An object's velocity states both the speed and direction of motion relative to a fixed reference point.
An image is virtual when it is formed by the eye reconstructing rays.
The voltage across a component is the electrical energy transferred by 1 coulomb of charge passing through the component.
A voltage divider is a circuit involving two resistors in series. The voltage across each resistor is determined by the value
of the resistors and the supply voltage, as given by the equation:
These circuits are often used in sensors.
A voltage follower is a special type of amplifier in which Vout = Vin
The wavelength is the distance from one point on a wave to the identical point on the next wave. This can be stated as the distance from a crest on a wave to the next crest on the wave.
A Wheatstone bridge is a circuit made of two voltage dividers connected in parallel with the same power supply. The midpoints of the two voltage dividers are connected with a voltmeter.
Work is the process by which energy is changed from one form to another. The scientific unit of work is the joule.
X-rays are high-energy electromagnetic waves produced by directing a beam of high-energy electrons at a metal target.
Young's modulus is defined as the ratio of the stress to the strain.