Understanding knowledge of A2 Physics - A2 物理理解性知识点.md

13 Gravitational fields

• analyse circular orbits in gravitational fields by relating the gravitational force to the centripetal acceleration it causes

• understand that a satellite in a geostationary orbit remains
1. orbital period of 24 hours,
2. orbiting from west to east,
3. directly above the Equator

• represent a gravitational field by means of field lines



• Binary star system have same period of both star.

14 Temperature

• Thermodynamic temperature does not depend on the property of any particular substance

15 Ideal gases

• amount of substance is an SI base quantity with the base unit mol

• Pressure-Volume graph:

16 Thermodynamics

• internal energy is determined by the state of the system and that it can be expressed as the sum of a random distribution of kinetic and potential energies associated with the molecules of a system. Ideal gas: potential energies in is negligible, We could assume that =0 and .

• relate a rise in temperature of an object to an increase in its internal energy (Which can be demonstrated in ideal gas by )

17 Oscillations

• The terms displacement, amplitude, period, frequency, angular frequency and phase difference in the context of oscillations displacement() amplitude () (maximum displacement) angular frequency () frequency () Phases difference(): Unit:

• analyse and interpret graphical representations of the variations of displacement, velocity and acceleration for simple harmonic motion

• a resistive force acting on an oscillating system causes damping

18 Electric fields

• represent an electric field by means of field lines

• Describe the effect of a uniform electric field on the motion of charged particles
1. F=qE, E is constant means F is constant. The Particle experience a constant force.
2. That is a projectile movement. We can analyse by devided the movement in horizontal and vertical.

19 Capacitance

• analyse graphs of the variation with time of potential difference, charge and current for a capacitor discharging through a resistor

20 Magnetic fields

• magnetic field is a field of force produced by moving charges or by permanent magnets

• represent a magnetic field by field lines

• The condition of a force act on a current-carrying conductor placed in a magnetic field
1. Remember
2. The direction of the current and magnetic field must not be parallel/ at a non-zero angle.

• determine the direction of the force on a current-carrying conductor/ charge moving in a magnetic field Fleming’s left-hand rule：



1. When determine the force on a current-carrying conductor,
• I is the direction of the current in conductor.
1. When determine the force on a charge moving,
• First determine the the polarity of the charge, if it's positive charge considering the direction of particle velocity as the direction of current flow.
• if it's negative charge considering the opposite direction of particle velocity as the direction of current flow.

• understand the use of a Hall probe to measure magnetic flux density

• describe the motion of a charged particle moving in a uniform magnetic field perpendicular to the direction of motion of the particle

• sketch magnetic field patterns due to the currents in a long straight wire, a flat circular coil and a long solenoid

• understand that the magnetic field due to the current in a solenoid is increased by a ferrous core

21 Alternating currents

• understand and use the terms period, frequency and peak value as applied to an alternating current or voltage period () frequency () peak value = Amplitude ()

• distinguish between root-mean-square (r.m.s.) and peak values root-mean-square (r.m.s.) in A.C: The value of a constant voltage/current that produces the same power in a resistor as the alternating voltage peak values: The maximum voltage/current

• distinguish graphically between half-wave and full-wave rectification

• analyse the effect of a single capacitor in smoothing, including the effect of the values of capacitance and the load resistance

22 Quantum physics

• understand that photoelectrons may be emitted from a metal surface when it is illuminated by electromagnetic radiation (when )

• understand that
• the photoelectric effect provides evidence for a particulate nature of electromagnetic radiation
• electron diffraction as interference and diffraction provide evidence for a wave nature

• the de Broglie wavelength as the wavelength associated with a moving particle , de Broglie wavelength exist means particle have momentum thus the particle is moving.

• Graphical Representation of Work Function：

• Number of photons in light beam:

• Given or Intensity and Area ()

• Note:

23 Nuclear physics

• there are discrete electron energy levels in isolated atoms
• Evident: discrete bar in emission spectra show that electrons in atoms can only transition between discrete energy levels

• the appearance and formation of emission and absorption line spectra



1. emission line spectra: an electron transitions from a higher energy level to a lower energy level, this results in the emission of a photon (in any direction).
2. absorption spectra: An atom can be raised to an excited state by the absorption of a photon

• sketch the variation of binding energy per nucleon with nucleon number

• that fluctuations in count rate provide evidence for the random nature of radioactive decay

• that radioactive decay is both spontaneous and random spontaneous: A process which cannot be influenced by environmental factors. random: A process in which the exact time of decay of a nucleus cannot be predicted.

• understand the exponential nature of radioactive decay, and sketch and use the relationship , where x could represent activity, number of undecayed nuclei or received count rate

24 Medical Phycics

• understand the use of X-rays in imaging internal body structures, including an understanding of the term contrast in X-ray imaging
• contrast: depends on difference between the intensities

• a tracer that decays by β+ decay is used in positron emission tomography (PET scanning)

• the gamma-ray photons from an annihilation event travel outside the body and can be detected, and an image of the tracer concentration in the tissue can be created by processing the arrival times of the gamma-ray photons

25 Astronomy and cosmology

• the use of standard candles to determine distances to galaxies
1. standard candles means L is known.
2. Radiant flux() can be detect.
3. Using to determine distant

• the lines in the emission spectra from distant objects show an increase in wavelength from their known values



1. an increase in wavelength means Red-shift
2. the origin wavelength of emission spectra is known
3. using Doppler redshift formula (given) to determine the value you nee