Physics Form 3

Indice

1. 1. Vectors and Scalars

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   • Scalar and vector quantities
   • Adding vectors along a line and at right angles
   • The parallelogram and triangle laws; the equilibrant
   • Resolving vectors and relative velocity
   • Summary

   Scalar and vector quantities A scalar quantity has magnitude (size) only. Examples: mass, distance, speed, time, temperature, energy, work, power and volume. A vector quantity has both magnitude and direction. Examples: displacement, velocity, acceleration, force, weight, momentum and electric field. Scalars are added…

2. 2. Friction

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   • What is friction?
   • Static, limiting and kinetic friction; the laws of friction
   • The coefficient of friction
   • Friction: useful, harmful and how to control it
   • Summary

   What is friction? Friction is the force that opposes the relative motion (or attempted motion) between two surfaces in contact. It acts along the surfaces, in the direction opposite to the motion. Friction is caused by the roughness of surfaces (tiny bumps catch on each other) and by attraction between the molecules of…

3. 3. Light: Curved Mirrors, Refraction and Colour

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   • Curved mirrors: shapes and key terms
   • Images formed by curved mirrors
   • The mirror formula and magnification
   • Refraction of light and Snell's law
   • Critical angle and total internal reflection
   • Dispersion and colour
   • Summary

   Curved (spherical) mirrors A concave (converging) mirror curves inwards; a convex (diverging) mirror bulges outwards. Key terms: pole (P) – centre of the mirror surface; centre of curvature (C) – centre of the sphere of which the mirror is part; radius of curvature (r) ; principal focus (F) – the point where rays…

4. 4. Optical Instruments

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   • Lenses: types and key terms
   • Images formed by lenses and the lens formula
   • The camera and the human eye
   • Defects of vision and their correction
   • Magnifying glass, microscope, telescope and projector
   • Summary

   Lenses A lens is a piece of transparent material with at least one curved surface that refracts light. A converging (convex) lens is thicker in the middle and brings parallel rays together at a real principal focus F . A diverging (concave) lens is thinner in the middle and spreads rays out so that they appear to come…

5. 5. Thermal Expansion

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   • Expansion and contraction: the particle explanation
   • Linear expansivity
   • Effects and uses of the expansion of solids
   • Expansion of liquids and the anomalous expansion of water
   • Expansion of gases: the gas laws
   • Summary

   What is thermal expansion? Thermal expansion is the increase in size of a substance when it is heated. When heated, the particles vibrate or move faster and push one another further apart. On cooling, substances contract . Gases expand most, liquids less and solids least for the same temperature rise. Expansion of…

6. 6. Transfer of Thermal Energy

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   • Conduction
   • Convection
   • Radiation
   • The vacuum flask and applications of heat transfer
   • Summary

   Introduction Thermal energy (heat) always flows from a region of higher temperature to a region of lower temperature. It is transferred in three ways: conduction , convection and radiation . Conduction Conduction is the transfer of heat through a material from particle to particle without the material itself moving.…

7. 7. Measurement of Thermal Energy

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   • Heat capacity and specific heat capacity
   • The method of mixtures and the calorimeter
   • The electrical method for specific heat capacity
   • Latent heat and change of state
   • Latent heat calculations, measurement and cooling by evaporation
   • Summary

   Heat capacity and specific heat capacity Different bodies need different amounts of heat to warm up by the same amount. The heat capacity (C) of a body is the quantity of heat needed to raise its temperature by 1 K: C = Q ÷ Δθ, unit J/K . The specific heat capacity (c) of a substance is the quantity of heat needed to…

8. 8. Vapour and Humidity

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   • Evaporation and boiling
   • Vapour pressure and boiling point
   • Humidity and its measurement
   • Dew point, dew, mist, clouds and rain
   • Summary

   Evaporation and boiling Evaporation is the change of a liquid into vapour at its surface, at any temperature. The fastest-moving molecules escape from the surface, so the average kinetic energy of those left behind falls – evaporation causes cooling . The rate of evaporation increases with: higher temperature, larger…

9. 9. Current Electricity

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   • E.m.f., terminal p.d. and internal resistance
   • Resistivity
   • Electrical energy and power
   • Domestic electrical installation
   • Fuses, circuit breakers, earthing and electrical safety
   • Summary

   E.m.f., terminal p.d. and internal resistance The electromotive force (e.m.f.), E of a cell is the energy it supplies per coulomb of charge driven round a complete circuit; it equals the p.d. across the cell when no current flows. When a current I flows, some energy is used inside the cell because of its internal…