'O' Level Revision PHYSICS Four 48K Spectrum Programs Rose Software LIGHT AND HEAT (C) ROSE SOFTWARE PHYSICS - LIGHT and HEAT The four 48K Spectrum programs cover the areas of "Light" and "Heat", and are intended as a useful revision guide for the "O" level student. The programs, compatible with the syllabus of most "O" level boards, instruct and test the student with a series of multiple choice questions, giving clear explantaions where necessary. There are also sections dealing with typical "O" level calculations, and these offer detailed help facilites together with an explanation of the correct answer if the student requires it. The formulae appropriate to the subject are listed in the programs. It is recommended that the student practise drawing the many diagrams shown. In particular, he should be familiar with the construction of ray diagrams. The four programs are menu driven and cover the following topics:- 1st Program "light 1" a) Nature of Light Light can be considered to travel in straight lines as demonstrated by the sharp edge of shadows and by the Pinhole Camera. b) Reflection in plane mirrors Laws of Reflection 1) The incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane. 2) The angle of incidence is equal to the angle of reflection. How the eye sees an image in a plane mirror. Lateral inversion. Images formed in two mirrors at right angles. c) Spherical mirrors C = centre of curvature F = principal focus P = pole Line CP = principal axis Distance CP = radius of curvature r Distance FP = focal length f r = 2f Rules for ray tracing 1) Rays parallel to the principal axis are reflected through F 2) Rays through the centre of curvature C are reflected back along the same path. 3) For a ray incident at P, angle of incidence = angle of reflection. Images formed by concave mirrors Depending on the position of the object, the image formed by a concave mirror can be either virtual and erect, or real and inverted. If the object is placed between F and P, then the image is virtual and erect. Images formed by convex mirrors The image formed is always virtual and erect and lies between P and F. Experiment to measure the focal length of a concave mirror. d) Refraction at plane surfaces Laws of Refraction 1) The incident ray AO and the refracted ray OB are on opposite sides of the normal NN' and all 3 are in the same plane. 2) Snell's law:- When light passes from one substance to another, the ratio of the sine of the angle of incidence i to the sine of the angle of refraction r is a constant (called the refractive index). Bent stick effect. Definition of refractive index as real depth _____________ apparent depth Total internal reflection and critical angle c Definition of refractive index as 1 ____________ SIN c Deviation of light by a prism. Angle of deviation. e) Action of lenses Formation of image by a diverging (concave) lens F = principal focus C = optical centre Distance FC = focal length Line through F and C = principal axis The image formed by a diverging lens is always virtual and erect. Formation of image by a converging (convex) lens The image formed by a convex lens can be either real or virtual. A virtual image is formed when the object is placed between F' and C. 2nd Program: "light 2" a) Optical Instruments Diagrams with questions on the car driving mirror, the magnifying glass, the slide projector, the single lens camera, and the eye. b) The Spectrum Refraction by a prism and the dispersion of white light. c) Diffraction and Interference Diffraction of waves through a narrow opening. Interference fringes formed by diffracted light from two narrow slits. Young's slits experiment. Measurement of the wavelength of light. d) Typical "O" Level Calculations A clear diagram accompanies each question. If the student is in difficulty, he can ask for help several times during each question. After giving his answer, he can choose to see a detailed explanation of the calculation if he wishes. e) Some useful formulae The formulae appertaining to the subject are listed. 3rd Program: "heat 1" a) Measurement of temperature Diagrams with questions on:- The mercury thermometer, The Absolute or Kelvin scale of temperature. b) Transmission of Heat. The transfer of thermal energy is brought about by conduction, convection and radiation. Conduction is the transfer of heat from hot to cold places through a substance without any movement of the substance as a whole. Experiment to compare thermal conductivities. Experiment to show water is a poor conductor of heat. Convection is the transfer of heat from hot to cold places through fluids, by the movement of the fluid itself. Ventilation of coal mines by convection. The domestic hot water system. Land and sea breezes. Radiation is the transfer of heat from hot to cold places as electro-magnetic waves (infrared). It can take place across a vacuum. Absorption of radiant heat by a surface. The Dewar flask (vacuum flask) c) Expansion The Bimetallic strip. The Electric Thermostat. The coefficient of linear expansion of a substance = expansion _______________________________________________ original length x rise in temperature Experiment to determine the coefficient of linear expansion of a metal. Water CONTRACTS on heating over the range 0° - 4°C Expansion of gases Boyle's Law:- pV = constant. Pressure x volume is constant for a fixed mass of gas at constant temperature. Apparatus to verify Boyle's Law. The General Gas Law:- pV = constant where T is _______ T temperature in Kelvin (absolutue). d) Specific Heat Capacity The specific heat capacity (c) of a substance is the heat required to raise unit mass of it through 1°C. Heat energy given out by a body = mc (mass x specific heat capacity x temperature change) Experiment to measure the specific heat capacity of a liquid by the method of electrical heating. 4th Program "heat 2" a) Change of State The specific latent heat of vapourisation of a substance is the quantity of heat required to change unit mass from liquid to vapour state without change of temperature. The specific latent heat of fusion of a substance is the quantity of heat required to change unit mass from solid to liquid state without change of temperature. Diagrams with questions on:- Cooling Napthalene solidifies at 80°C, and the temperature remains at 80°C for several minutes. Example to find the amount of heat required to change a quantity of ice into steam, leading the student through the calculations step by step, with diagrams. Cooling by evaporation. To find the specific latent heat of steam by a continuous flow experiment. Saturated vapours:- A saturated vapour is one which is in a state of dynamic equilibrium with its surroundings. Saturation vapour pressure (svp) svp does not depend on volume. Experiment to demonstrate the variation of svp with temperature. svp and boiling point. b) Some useful formulae The formulae appertaining to the subject are listed. c) Typical "O" level calculations A clear diagram accompanies each question. If the student is in difficulty, he can ask for help several times during each question. After giving his answer, he can choose to see a detailed explanation of the calculation if he wishes. TO LOAD A PROGRAM:- Ensure the heads of your cassette deck are clean and demagnetised. Key in LOAD "light 1" (for the 1st. program) and press ENTER OTHER SPECTRUM TITLES PUBLISHED BY ROSE SOFTWARE INCLUDE:- "O" Level Maths Revision - GEOMETRY "O" Level Maths Revision - TRIGONOMETRY "O" Level Maths Revision - EQUATIONS & INEQUALITIES "O" Level French Vocabulary Revision. Intermediate Maths 1 Intermediate English 1 Intermediate Maths 2 Intermediate English 2 Young Learners 1 Primary Arithmetic Young Learners 2 Highway Code Quiz Send sae for free brochure of all our products to:- ROSE SOFTWARE, 148 Widney Lane, Solihull, West Midlands, B91 3LH Copyright 1984 Rose Software. No part of this recording shall be reproduced, hired or loaned without written permission. While every precaution has been taken in the preparation of this recording, the publisher assumes no responsi- bility for errors nor liabilty for damages arising from its use.