Physics (物理)

This topic examines the concept of thermal energy and transfer processes which are crucial for the maintenance and quality of our lives. Particular attention is placed on the distinction and relationships among temperature, internal energy and energy transfer. Students are also encouraged to adopt microscopic interpretations of various important concepts in the topic of thermal physics. Calculations involving specific heat capacity will serve to complement the theoretical aspects of heat and energy transfer. The practical importance of the high specific heat capacity of water can be illustrated with examples close to the experience of students. A study of conduction, convection and radiation provides a basis for analysing the containment of internal energy and transfer of energy related to heat. The physics involving the change of states is examined and numerical problems involving specific latent heat are used to consolidate the theoretical aspects of energy conversion. The ideal gas law relating the pressure, temperature and volume of an ideal gas was originally derived from the experimentally measured Charles’ law and Boyle’s law. Many common gases exhibit behaviour very close to that of an ideal gas at ambient temperature and pressure. The ideal gas law is a good approximation for studying the properties of gases because it does not deviate much from the ways that real gases behave. The kinetic theory of gases is intended to correlate temperature to the kinetic energy of gas molecules and interpret pressure in terms of the motion of gas molecules.

Motion is a common phenomenon in our daily experience. It is an important element in physics where students learn to describe how objects move and investigate why objects move in the way that they do. In this topic, the fundamentals of mechanics in kinematics and dynamics are introduced, and the foundation for describing motion with physics terminology is laid. Various types of graphical representation of motion are studied. Students learn how to analyse different forms of motion and solve simple problems relating to uniformly accelerated motion. They also learn about motion in one or two dimensions and rules governing the motion of objects on Earth. The concept of inertia and its relation to Newton’s First Law of motion are covered. Simple addition and resolution of forces are used to illustrate the vector properties of forces. Free-body diagrams are used to work out the net force acting on a body. Newton’s Second Law of motion, which relates the acceleration of an object to the net force, is examined. The concepts of mass, weight and gravitational force are introduced. Newton’s Third Law of motion is related to the nature of forces. The study of motion is extended to two dimensions, including projectile motion and circular motion which lead to an investigation of gravitation. Work is a process of energy transfer. The concepts of mechanical work done and energy transfer are examined and used in the derivation of kinetic energy and gravitational potential energy. Conservation of energy in a closed system is a fundamental concept in physics. The treatment of energy conversion is used to illustrate the law of conservation of energy, and the concept of power is also introduced. Students learn how to compute quantities such as momentum and energy in examples involving collisions. The relationship among the change in the momentum of a body, impact time and impact force is emphasised.

This topic examines the basic nature and properties of waves. Light and sound, in particular, are also studied in detail. Students are familiar with examples of energy being transmitted from one place to another, together with the transfer of matter. In this topic, the concept of waves as a means of transmitting energy without transferring matter is emphasised. The foundations for describing wave motion with physics terminology are laid. Students learn the graphical representations of travelling waves. The basic properties and characteristics displayed by waves are examined; reflection, refraction, diffraction and interference are studied, using simple wavefront diagrams. Students acquire specific knowledge about light in two important aspects. The characteristics of light as a part of the electromagnetic spectrum are studied. Also, the linear propagation of light in the absence of significant diffraction and interference effects is used to explain image formation in the domain of geometrical optics. The formation of real and virtual images using mirrors and lenses is studied with construction rules for light rays. Sound as an example of longitudinal waves is examined and its general properties are compared with those of light waves. Students also learn about ultrasound. descriptions of musical notes are related to the terminology of waves. The general The effects of noise pollution and the importance of acoustic protection are also studied.

This topic examines the basic principles of electricity and magnetism. The abstract concept of an electric field is introduced through its relationship with the electrostatic force. The inter-relationships among voltage, current, resistance, charge, energy and power are examined and the foundation for basic circuitry is laid. As electricity is the main energy source in homes and electrical appliances have become an integral part of daily life, the practical use of electricity in households is studied. Particular attention is paid to the safety aspects of domestic electricity. The concept of magnetic field is applied to the study of electromagnetism. The magnetic effects of electric current and some simple magnetic field patterns are studied. Students also learn the factors that affect the strength of an electromagnet. A magnetic force is produced when a current-carrying conductor is placed in a magnetic field. An electric motor requires the supply of electric current to the coil in a magnetic field to produce a turning force causing it to rotate. The general principles of electromagnetic induction are introduced. Electrical energy can be generated when there is relative motion between a conductor and a magnetic field. Generators reverse the process in motors to convert mechanical energy into electrical energy. The operation of simple d.c. and a.c. generators are studied. Students learn how a.c. voltages can be stepped up or down with transformers. The system by which electrical energy is transmitted over great distances to our homes is also studied.

In this topic, nuclear processes are examined. Ionizing radiation is very useful in industrial and medical fields but at the same time is hazardous to us. Nuclear radiation comes from natural and artificial sources. It is essential for students to understand the origin of radioactivity, the nature and the properties of radiation. Students should also learn simple methods to detect radiation and identify major sources of background radiation in our natural environment. Simple numerical problems involving half-lives are performed in order to understand the long-term effects of some radioactive sources. The potential hazards of ionizing radiation are studied scientifically and in a balanced way by bringing in the concept of dosage. In the atomic model, the basic structure of a nuclide is represented by a symbolic notation. Students learn the concepts of isotopes. They are also introduced to fission and fusion, nature’s most powerful energy sources.

Astronomy is the earliest science to emerge in history. The methods of measurement and the ways of thinking developed by early astronomers laid the foundation of scientific methods which influenced the development of science for centuries. The quest for a perfect model of the universe in the Renaissance eventually led to the discovery of Newton’s law of universal gravitation and the laws of motion. This had a profound influence on the subsequent rapid development in physics. Using physical laws in mathematical form to predict natural phenomena, and verifying these predictions with careful observation and experimentation, as Newton and other scientists did some three hundred years ago, has become the paradigm of modern physics research. Physics has become the cornerstone of modern astronomy, revolutionising our concepts of the universe and the existence of humankind. Modern developments in space science, such as the launch of spacecraft and artificial satellites, still rely on Newtonian physics. In this topic, students have an opportunity to learn principles and scientific methods underpinning physics, and to appreciate the interplay between physics and astronomy in history, through studying various phenomena in astronomy and knowledge in space science. Students are first given a brief introduction to the phenomena of the universe as seen in different scales of space. They are also encouraged to perform simple astronomical observations and measurements. Through these processes, they can acquire experimental skills, and become more familiar with the concept of tolerance in measurement. A brief historic review of geocentric model and heliocentric model of the universe serves to stimulate students to think critically about how scientific hypotheses were built on the basis of observation. Kepler’s third law and Newton’s law of gravitation are introduced with examples of astronomy. Kepler’s third law for circular orbits is derived from the law of gravitation and concepts of uniform circular motion, including centripetal acceleration. Besides the motion of planets, moons and satellites, latest astronomical discoveries can also serve as examples to illustrate the applications of these laws. The concepts of mass and weight are applied. Feeling weightlessness in a spacecraft orbiting the Earth is explained in terms of the fact that acceleration under gravity is independent of mass. The expression for gravitational potential energy can be obtained from the law of gravitation and work-energy theorem. Motions of artificial satellites are explained by the conservation of mechanical energy in their orbits. The meaning of escape velocity, together with its implications for the launching of a rocket, are introduced. In the last part of this topic, students are exposed to astronomical discoveries, including the basic properties and classification of stars and the expansion of the universe. As only a simple, heuristic and qualitative understanding of these topics is expected, students are encouraged to learn actively by reading popular science articles and astronomical news – which promotes self-directed learning. Also, oral or written presentation of what they have learned may serve to improve their communication skills.

The nature of the smallest particles making up all matter has been a topic of vigorous debate among scientists, from ancient times through the exciting years in the first few decades of the 20th century to the present. Classical physics deals mainly with particles and waves, as two distinct entities. Substances are made of very tiny particles. Waves, such as those encountered in visible light, sound and heat radiations, behave very differently from particles. At the end of the 19th century, particles and waves were thought to be very different and could not be associated with each other. When scientists looked more closely at the nature of substances, contradictory phenomena that confused scientists began to appear. Classical concepts in Mechanics and Electromagnetism cannot explain the phenomena observed in atoms, or even the very existence of atoms. Studies on the structure of an atom and the nature of light and electrons revealed that light, the wave nature of which is well known, shows particle properties, and electrons, the particle nature of which is well known, show wave properties. In this elective topic, students learn about the development of the atomic model, the Bohr’s atomic model of hydrogen, energy levels of atoms, the characteristics of line spectra, the photo-electric effect, the particle behaviour of light and the wave nature of electrons, i.e. the wave-particle duality. Through the learning of these physical concepts and phenomena, students are introduced to the quantum view of our microscopic world and become aware of the difference between classical and modern views of our physical world. Students are also expected to appreciate the evidence-based, developmental and falsifiable nature of science. Advances in modern physics have led to many applications and rapid development in materials science in recent years. This elective includes a brief introduction to nanotechnology, with a discussion on the advantages and use of transmission electron microscopes (TEM) and scanning tunnelling microscopes (STM), as well as some potential applications of nano structures. Nanotechnologies have been around for hundreds of years, although the underlying physics was not known until the 20th century. For example, nano-sized particles of gold and silver have been used as coloured pigments in stained glass since the 10th century. With better understanding of the basic principles, more applications have been found in recent years. These applications include the potential use of nano wires and nano tubes as building materials and as key components in electronics and display. Nano particles are used in suntan lotions and cosmetics, to absorb and reflect ultra-violet rays. Tiny particles of titanium dioxide, for example, can be layered onto glass to make self-cleaning windows. As in any newly developed area, very little is known, for example, about the potential effects of free nano particles and nano tubes on the environment. They may cause hazards to our health and might lead to health concerns. Students are, therefore, expected to be aware of the potential hazards, and issues of risk and safety to our life and society in using nanotechnologies. In studying this elective topic, students are expected to have basic knowledge about force, motion, and waves. Some basic concepts of covalent bonds of electrons would be helpful in understanding the structures and special properties of nano materials. Knowledge of electromagnetic forces, electromagnetic induction and electromagnetic spectrum is also required.

The ability of human beings to use various forms of energy is one of the greatest developments in human history. Electrical energy brings cities to life. Modern transportation powered by energy links peoples together. Modern society is geared to using electricity as a main energy source. There are many reasons why electricity is the most common energy source used at home and in the office. This elective topic begins by reviewing domestic appliances for lighting, cooking and air-conditioning. These appliances show how physics principles are used to make our homes better and more comfortable places to live in. Students investigate the total amount of energy transferred when these appliances are in operation. They also learn how to calculate the cost from power rating of the appliances. The idea of energy changes being associated with energy transfer is raised, and students identify the energy changes associated with a range of appliances. This leads into the introduction of the Energy Efficiency Labelling Scheme informing the public to choose energy-efficient household appliances for saving energy. Building and transportation provide situations for students to study the factors affecting energy performance in real contexts. Building materials provide the starting point for discussion of the thermal properties of different materials to transfer energy; and this leads to consideration of a building design to minimise energy use and provide an appropriate internal environment without sacrificing its quality. Through the use of electric motors as energy converters in vehicles, students study the efficiency of electric motors compared to internal combustion engines, in the attempt to reduce air pollution. There are many energy sources used as fuel that can be converted into electricity. The current fuels used for generating electricity in Hong Kong include coal, petroleum, natural gas, nuclear fuel and pump storage. Students compare the efficiency of different fuels and different ways of using the same fuel. Through a consideration of the design features of a solar cooker, students investigate conduction, convection and radiation as means of transferring energy from nature. Different sources of energy have different environmental effects on society. When fossil fuels burn, a large amount of pollutants are discharged into the air. The pollutants cause atmospheric pollution, reduce air quality and contribute to the greenhouse effect which may warm and damage the Earth. Whereas nuclear power stations are very efficient, the disposal of dangerous radioactive waste materials continues to be a problem. The growing concern about the environmental impact of energy polluting the environment has made environmentally friendly and alternative energy sources worth considering. In this connection, emphasis is placed on the energy conservation principle, to encourage efficient energy usage in order to maintain and improve the quality of the environment. Energy efficiency can be described simply using an input-output model. For example, a solar cell can be understood generally as a transducer that has the solar radiation as input and a useful form of electrical energy as the output. Despite the fact that Hong Kong has no indigenous energy sources, solar cells and wind power are introduced as local contextual examples to illustrate the concept of renewable energy sources. This elective topic increases students’ understanding of the application of physics, the uses of different energy sources and the implications of energy efficiency to the environment.

This elective is concerned with the basic physics principles underlying human vision and hearing to make sense of the environment. It begins by considering the structures of the eye and its optical system for adjusting to different object distances. Defects of vision and the study of their corrections are introduced. Resolution is introduced to explain the fineness of detail discernible by the eye. The question of how colour vision is generated leads to the study of the rods and cones in the retina. Rods are responsible for vision in dim light while cones are responsible for the more acute vision experienced in ordinary daylight conditions. A brief look at the structure of the ear serves to introduce students to concepts of transferring energy using a transducer and how different frequencies of sound waves are discriminated in the inner ear. Attention is then given to the applications of sound waves and visible light for seeing inside the body. A brief look at the work of ultrasound scanners and endoscopes serves to introduce students to pulse-echo and the total internal reflection of waves. Ionizing radiation, such as X-rays and gamma rays, is introduced to students as an alternative means of examining the anatomical structures and functions of a body for medical diagnosis. In hospitals and clinics around the world, literally hundreds of thousands of patients daily receive medical imaging tests in which X-rays, radionuclides, ultrasound and computed tomography (CT) are used. In virtually all these devices, physics has developed from our understanding of the electromagnetic spectrum, the radioactivity of specific nuclides and the wave properties of ultrasound beams. Such devices have enabled radiologists to see through the body without surgery. The medical uses of radioactive substances are introduced to students and the ways in which gamma radiation can be detected by gamma cameras to produce images for medical diagnosis are considered. It should be emphasised that the development of new imaging modalities is an evolutionary process. It may start with the discovery of a new physical phenomenon or a variation of an existing one. At all stages, expertise in physics is essential. There is considerable interest in medical physics in the field of radiation oncology, nuclear medicine and radiology, and some students will want to know more about such developments.