Revision - Exploring Physics definitions Flashcards
What is electric current?
Electric current is defined as the rate of flow of charge.
What is the unit of charge?
The unit of charge, the Coulomb, is defined as being one ampere in a second.
What is conventional current?
The direction that a positive charge carrier would move in the circuit, from the positive side of the power supply towards the negative side.
What is mean drift velocity?
Mean drift velocity is the average displacement per unit time of electrons along the wire in the direction of the positive terminal.
What is number density?
Number density is the number of charge carriers per unit volume.
What is a volt?
Volt is defined as one Joule per Coulomb.
What is potential difference?
Potential difference is the energy transferred per unit charge when electrical energy is converted to another form of energy.
What is electromotive force (emf)?
Electromotive force (emf) is the energy transferred per unit charge when another form of energy is converted into electrical energy.
What is power?
Power is the rate of energy transfer.
What is resistance?
Resistance is the ratio of voltage to current.
What is an Ohm?
An Ohm is one volt per ampere.
What is Ohm’s law?
Ohm’s law states that for a metallic conductor at constant temperature, the potential difference is proportional to current.
What is resistivity?
Resistivity is defined as RA/L, where R is the resistance of a wire of that material, A is the cross-sectional area, and L is the length. Resistivity is measured in Ωm.
What is a kilowatt hour?
A kilowatt hour is the energy transferred by a 1kW device operating for a time of 1 hour.
What does Kirchhoff’s first law state?
Kirchhoff’s first law states that the sum of currents entering a point equals the sum of currents leaving that point (conservation of charge).
What does Kirchhoff’s second law state?
Kirchhoff’s second law states that the sum of the e.m.f.s around a circuit loop equals the sum of p.d.s around that loop (conservation of energy).
What is internal resistance?
Internal resistance is the resistance in a battery or power source which causes a voltage drop, ‘lost volts’, when current flows.
What is a progressive wave?
A progressive wave is a wave that transfers energy from a source through the surroundings by means of oscillations.
What are transverse waves?
Transverse waves are vibrations that are at right angles to the direction of energy transfer (e.g., light).
What are longitudinal waves?
Longitudinal waves are vibrations that are parallel to the direction of energy transfer (e.g., sound).
What is displacement in a wave?
Displacement is defined as the distance of a point on a wave above or below the undisturbed position.
What is amplitude?
Amplitude is defined as the maximum displacement of any wave from its undisturbed position.
What is wavelength?
Wavelength is defined as the minimum distance between two adjacent points in phase on a progressive wave.
What is the time period of a wave?
The time period is defined as the time taken for one complete oscillation or wavelength.
What is frequency?
Frequency is the number of oscillations (wavelengths) passing a point per unit time (measured in Hertz).
What is wave speed?
Wave speed is the distance travelled per unit time.
What is phase difference?
Phase difference is the angle by which one wave lags or leads another. Waves that are in phase have a phase difference of 0 or 2π radians, whereas waves that are exactly out of phase have a phase difference of π radians.
What is reflection?
Reflection is the change in direction of a wave at the interface between two media back into the original medium.
What is refraction?
Refraction is a change in direction of a wave due to the wave speeding up or slowing down as it changes medium.
What is the critical angle?
The critical angle is the angle of incidence of a ray of light when the angle of refraction equals 90 degrees. If the angle of incidence is greater than the critical angle, total internal reflection occurs.
What is refractive index?
Refractive index is the ratio of the speed of light in a vacuum to the speed of light in a medium.
What is plane polarisation?
Plane polarisation is when a transverse wave has all of the vibrations occurring in one plane at right angles to the direction of energy transfer.
What is diffraction?
Diffraction is the spreading out of waves around an obstacle or through a gap. The gap or obstacle must be of size similar to the wavelength of the wave for diffraction to occur (same order of magnitude).
What is intensity?
Intensity is power per unit cross-sectional area. Intensity is proportional to amplitude squared.
What is the Principle of Superposition?
The Principle of Superposition states that when two coherent waves interfere, the sum of their displacements is equal to the displacement of the resultant wave.
What is interference?
Interference is the superposition of two progressive waves from coherent sources to produce a resultant wave with displacement equal to the sum of the individual displacements of the two waves.
What happens during constructive interference?
If two waves meet in phase or with path difference nλ, then there will be constructive interference.
What happens during destructive interference?
If two waves meet out of phase by 180° (antiphase) or with path difference nλ + 1/2λ, then there will be destructive interference.
What is coherence?
Coherence is when two waves are emitted with a constant phase difference, same frequency, polarised in the same plane, and similar amplitude. Coherence is a condition for interference.
What is path difference?
Path difference is the difference in distance from one source to the detector compared with the distance from another source to the detector.
What is a node in a stationary wave?
A node is a point in a stationary wave where the amplitude is always zero.
What is an antinode?
An antinode is a point on a stationary wave of maximum amplitude.
What is the fundamental mode of vibration?
The fundamental mode of vibration is the lowest frequency at which a standing wave can be formed.
What are harmonics?
Harmonics are whole number multiples of the fundamental frequency of a stationary wave.
What is a photon?
A photon is defined as a quantum of energy of electromagnetic radiation.
What is an electronvolt?
An electronvolt is the energy gained when one electron travels through a potential difference of one volt.
What is the photoelectric effect?
The photoelectric effect is the emission of photoelectrons from the surface of a metal when photons are incident with energy E=hf greater than the work function of the metal.
What is threshold frequency?
Threshold frequency is the minimum frequency required to release electrons from the surface of a metal.
What is threshold wavelength?
Threshold wavelength is the maximum wavelength that will release electrons from the surface of a metal.
What is the work function?
The work function is the minimum amount of energy required by an electron to escape its surface.
What is the De Broglie wavelength?
The De Broglie wavelength is defined as the ratio of the Planck constant to the momentum of the electron.
What does Faraday’s law state?
Faraday’s law states that the magnitude of the induced emf is equal to (minus) the rate of the change of flux linkage.
What does Lenz’s law state?
Lenz’s law states that the direction of the emf is such that it will try to oppose the change that caused it.
What is capacitance?
Capacitance is charge stored per unit potential difference.
What is a farad?
A farad is defined as coulomb per volt.
What is time constant?
Time constant is the time taken for the current, potential difference, or charge to fall to e^-1 of any initial value.
What is electric field strength?
Electric field strength is defined as force per unit positive charge.
What is Coulomb’s Law?
Coulomb’s Law states that the force between two charged particles is proportional to the product of the charges and inversely proportional to their separation squared. The constant of proportionality can be written in terms of the permittivity of free space ε0.
What is electric potential?
Electric potential is the work done in bringing a unit charge from infinity to the point. At infinity, electric potential is zero.
What is magnetic flux density?
Magnetic flux density B is the force F acting per unit length l of a conductor carrying a unit current (Field and conductor at 90˚).
What is a Tesla?
1 Tesla is the magnetic flux density that will produce a force of 1N on 1m of wire carrying a current of 1A perpendicular to the magnetic field.
What is magnetic flux?
Magnetic flux is magnetic flux density multiplied by the area at 90˚ to the magnetic field.
What is a Weber?
A Weber is the magnetic flux when a magnetic field of magnetic flux density 1 Tesla passes at right angles through an area of 1 square metre.
What is Fleming’s left hand rule?
Fleming’s left hand rule is for the force on a moving charge in a magnetic field: Thumb: Force; First finger: Magnetic field; Second finger: Conventional current (given by a positive charge carrier).
What is magnetic flux linkage?
Magnetic flux linkage is the product of magnetic flux and the number of turns on the wire.
What is beta minus decay?
Beta Minus Decay occurs in nuclei with too many neutrons. A neutron decays into a proton plus an electron (𝛽−) and an anti-neutrino.
What is beta plus decay?
Beta Plus Decay occurs in nuclei with too many protons. A proton decays into a neutron plus a positron (𝛽+) and a neutrino.
What are isotopes?
Isotopes are atoms of the same chemical element with the same number of protons but different numbers of neutrons.
What is a hadron?
A hadron is a particle that is not fundamental and is made of quarks.
What is a baryon?
A baryon is a particle made of 3 quarks.
What is a meson?
A meson is a particle made of a quark and an antiquark.
What is a lepton?
A lepton is a particle that is fundamental.
What does spontaneous mean in nuclear decay?
Spontaneous means not affected by physical conditions such as temperature or pressure.
What does random mean in nuclear decay?
Random means you can’t predict which individual nucleus will be next to decay or when it will happen.
What is activity in nuclear physics?
The activity of a source is the number of nuclei that decay per unit time.
What is decay constant?
The decay constant of a radio-nuclide is the probability that an individual nucleus will decay within a unit of time.
What is half-life?
Half-life (t1/2) is the average time taken for half the radioactive nuclei to decay.
What is mass defect?
Mass defect is the difference in mass between a bound system (nucleus) and the mass of its constituent parts (nucleons).
What is binding energy?
Nuclear binding energy is the minimum energy required to split a nucleus completely into separate protons and neutrons.
What is binding energy per nucleon?
Binding energy per nucleon is the nuclear binding energy divided by the number of nucleons.
What is induced fission?
Induced fission occurs when a thermal neutron is absorbed by an unstable nucleus, causing the nucleus to split into two smaller nuclei, releasing energy and several fast-moving neutrons.
What is the piezoelectric effect?
The piezoelectric effect involves pulses of alternating voltage applied to a crystal to make it vibrate and produce ultrasound of the same frequency.
What is attenuation?
Attenuation is the reduction in intensity due to absorption in a material.
What is acoustic impedance?
Acoustic impedance is defined as the density of tissue multiplied by the speed of ultrasound in tissue.
What is the Doppler Effect?
The Doppler Effect is the change in observed frequency (or wavelength) due to relative motion between the source of a wave and the observer.
