Definition of A2 Physics - A2 物理定义.md

12 Motion in a Circle

• Radian: The angle subtended at the centre of a circle by an arc equal in length to the radius of the circle.

• Angular Speed:() The rate of change of the angle with respect to time.

• Centripetal Acceleration/Force: A force of constant magnitude that is always perpendicular to the direction of velocity causes centripetal acceleration, resulting in changing the direction of the velocity.

13 Gravitational Fields

• Gravitational Field: A region of space around a mass within which other masses experience a force of attraction.

• Gravitational Field Strength:() The force experienced by a unit mass due to a gravitational field.

• Gravitational Potential:() The work done per unit mass in bringing a mass from infinity to a point in space.

14 Temperature

• Thermal Equilibrium: The state in which all parts of a system have the same temperature and no net thermal energy exchange in the system.

• Specific Heat Capacity: The amount of thermal energy required to raise the temperature of 1 kg of a substance by 1 K.

• Specific Latent Heat of Fusion/Vaporization: The thermal energy required to convert 1 kg of (solid to liquid/ liquid to gas) with no change in temperature.

• Absolute Zero: The lowest possible temperature where all molecules stop moving and no heat energy remains in a substance, known as 0 K.

15 Ideal Gases

• Ideal gases obey: , The product of Pressure and Volume of a gas in proportional to the thermodynamic Temperature.

• The Kinetic Theory of Gases:

• T The time of a collision is negligible compared to the time between collisions

• F There are no forces of attraction or repulsion between the molecules

• R The molecules are in continuous random motion

• E Molecules of gas behave as identical, hard, perfectly elastic spheres

• V The volume of the molecules is negligible compared to the volume of the container TF REV. TF boys旋转（REV是Revolution旋转 ）（P.S. 无意冒犯TF boys）

16 Thermodynamics

• First Law of Thermodynamics: The change in internal energy of a system is equal to the heat added to the system minus the work done by the system on its surroundings.
• ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system.

17 Oscillations

• Simple Harmonic Motion: A type of periodic motion where the acceleration is directly proportional to the negative of displacement.

• Resonance: When the forced frequency is equal to the natural frequency of the system, causing the system to oscillate with maximum amplitude.

18 Electric Fields

• Electric Field: An electric field is a region of space in which an electric charge experience a force.

• Electric Potential:() The work done per unit positive charge in bringing a small test charge from infinity to the point.

19 Capacitance

• Capacitance in Isolated Spherical Conductors: For an isolated spherical conductor, it is the charge stored on the surface of sphere per unit potential created by that charge on the sphere.

• Capacitance in Parallel Plate Capacitors: For a parallel plate capacitor, it is the charge stored on one plate per unit voltage across the metal plates.

20 Magnetic Fields

• Magnetic Field: A region of space where a permanent magnet, current-carrying wire, or moving charged particle experiences a force.

• Magnetic Flux Density:() Force acting per unit current per unit length on a wire placed at right angles to the magnetic field.

• Magnetic Flux:() The product of the magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density.

• Faraday’s Law: The magnitude of the induced e.m.f is directly proportional to the rate of change in magnetic flux linkage.

• Lenz’s Law: The induced e.m.f acts in such a direction to produce effects which oppose the change causing it.

21 Alternating currents

• Rectification: The process of converting alternating current(A.C)/voltage into direct current(D.C)/voltage.

22 Quantum Physics

• Photon: A quantum of electromagnetic radiation energy.

• Photoelectric Effect: The photoelectric effect is the phenomena in which electrons are emitted from the surface of a metal upon the absorption of electromagnetic radiation.

• Work Function:() The minimum energy required to release a photoelectron from the surface of a material.

• Threshold Frequency: The minimum frequency of incident electromagnetic radiation required to remove a photoelectron from the surface of a metal.

• Threshold Wavelength: The longest wavelength of incident electromagnetic radiation that would remove a photoelectron from the surface of a metal.

23 Nuclear Physics

• Mass Defect: The difference between the mass of a nucleus and the sum of the individual masses of its protons and neutrons.

• Nuclear Binding Energy: Energy required to separate the nucleons (in the nucleus)  to infinity.

• Radioactive decay: The spontaneous disintegration of a nucleus to form a more stable nucleus, resulting in the emission of an alpha, beta or gamma particle.

• Activity:() The decrease in the number of radioactive nuclei per unit time.

• Decay Constant:() The probability that an individual nucleus will decay per unit of time.

• Half-Life:() The time taken for the initial number of nuclei to reduce by half.

24 Medical Physics

• Piezoelectric Effect/Crystal: A piezo-electric crystal changes shape when a p.d. is applied across it and generates an e.m.f. when its shape changes.

• Specific Acoustic Impedance:() The product of the speed of the ultrasound in the medium and the density of the medium.

• Tracer: A substance containing radioactive nuclei that can be introduced into the body and is then absorbed by the tissue being studied.

• Annihilation: When a particle interacts with its antiparticle and mass is converted to energy. (in Annihilation of PET scan, electron interacts with positron and emitting 2 photons in opposite direction).

• computed tomography (CT): scanning produces a 3D image of an internal structure by first combining multiple X-ray images taken in the same section from different angles to obtain a 2D image of the section, (then repeating this process along an axis and combining 2D images of multiple sections)

25 Astronomy and Cosmology

• Luminosity:() The total amount of energy emitted by a star, galaxy, or other astronomical object per unit time.
• An object of known luminosity = Standard Candle

• Red-shift: the phenomenon where light or other electromagnetic radiation from an object moves towards the red end of the spectrum as it reaches an observer.
• This shift towards longer wavelengths occurs when the source of the light is moving away from the observer due to Doppler effect.
• It's shows all the object is moving away from the Earth.

• Hubble's Law: The recession speed of galaxies moving away from Earth is proportional to their distance from the Earth.