RI Chap 4 Energy and Fields Lecture Notes

4 ENERGY & FIELDS H2 Physics 9749 Content Page 1.1 Introduction 2 1.2 Systems 2 1.3 Energy Stores & Transfers 3 1.4 Energy Transfers & Work Done 5 1.5 Kinetic Energy 9 1.6 Elastic Potential Energy 10 1.7 Fields 111 1.8 Gravitational Potential Energy 133 1.9 Electric Potential Energy 199 1.10 The Principle of Conservation of Energy 233 1.11 Power & Efficiency 244 Learning Outcomes Candidates should be able to: (a) show an understanding that physical systems can store energy, and that energy can be transferred from one store to another. (b) give examples of different energy stores and energy transfers, and apply the principle of conservation of energy to solve problems. (c) show an understanding that work is a mechanical transfer of energy, and define and use work done by a force as the product of the force and displacement in the direction of the force. (d) derive, from the definition of work done by a force and the equations for uniformly accelerated motion in a straight line, the equation 21 2 KE mv= . (e) recall and use the equation 21 2 KE mv= to solve problems. (f) show an understanding of the concept of a field as a region of space in which bodies may experience a force associated with the field. (g) define gravitational field strength at a point as the gravitational force per unit mass on a mass placed at that point, and define electric field strength at a point as the electric force per unit charge on a positive charge placed at that point.

Page | 2 (h) represent gravitational fields and electric fields by means of field lines (e.g. for uniform and radial field patterns), and show an understanding of the relationship between equipotential surfaces and field lines. [Equipotential surfaces not in H1 syllabus] (i) show an understanding that the force on a mass in a gravitational field (or the force on a charge in an electric field) acts along the field lines, and the work done by the field in moving the mass (or charge) is equal to the negative of the change in potential energy. (j) distinguish between gravitational potential energy, electric potential energy and elastic potential energy. (k) recall that the elastic potential energy stored in a deformed material is given by the area under its force-extension graph and use this to solve problems. (l) define power as the rate of energy transfer. (m) show an understanding that mechanical power is the product of a force and velocity in the direction of the force. (n) show an appreciation for the implications of energy losses in practical devices, and solve problems using the concept of efficiency of an energy transfer as the ratio of useful energy output to total energy input. 1.1 Introduction Now that we have learnt about the basics of forces and its relationship with motion, it is time to turn our attention towards another important concept in Physics – energy. Using energy to analyse the motion of systems can be very powerful,