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BTEC Level 3 Nationals in Applied Science
Additional Guidance
Unit 5 – Section C – Thermal physics, materials and fluids
Essential Content Additional Guidance
C1 Thermal physics in domestic and industrial
applications Learners should:
Be able to use the following quantities and units: o power, watt (W), kilowatt (kW), megawatt (MW), gigawatt (GW) know that the unit of energy is the joule (J) and that power is the energy transferred each second i.e. watts = joules/time (J/s) be able to convert between these units and multiples of units, e.g. know that 1 GW = 109 W o convert °C to K (^) be able to convert between these units o pressure (Pascals (Pa), Newton per metre squared (Nm- (^2) )) know that Force is measured in newtons (N) understand that pressure is force per unit of area be able to substitute values for any two of pressure, P or force, F or area, A into the equation P = F/A and calculate a value for the other term be able to re-arrange the equation Know the following definitions: o work done as energy transferred understand that whenever work is done energy is transferred from one form to another. The amount of work done in J = the amount of energy transferred in J o work done as force × distance moved in direction of force ( W = F × ∆ s ) be able to substitute values for any two of work done, W or force, F or distance moved in the direction of the force, ∆ s into the equation ( W = F × ∆ s ) and calculate a value for the other term be able to re-arrange the equation o work done by a gas as pressure × change in volume of (^) be able to substitute values for any two of work done, W or pressure of gas, p or
gas ( W = p × ∆ V ) change in volume of the gas, ∆ V into the equation ( W = p × ∆ V ) and calculate a value for the other term be able to re-arrange the equation know that this equation can be combined with the equation above it to give the unit for pressure as Nm-2, e.g. F × ∆ s = p × ∆ V Be able to calculate efficiency using the relationships: o efficiency = work output / energy input be able to substitute values for any two of efficiency or work (or energy) output or energy (or work) input and calculate a value for the other term be able to re-arrange the equation o for heat engines: efficiency = 1 - (Q out / Qin) know that a heat engine is any device that converts heat or thermal energy into useful work or other useful forms of energy, e.g. burning coal in a power station to produce electrical energy be able to substitute values for any two of efficiency or work (or energy or power) output, Qout or energy (or work or power) input, Qin and calculate a value for the other term be able to re-arrange the equation o maximum theoretical efficiency = 1 - (T C / TH) ^ be^ able to substitute values for any two of maximum theoretical efficiency or temperature in kelvins of the output (exhaust or cold reservoir), TC or temperature in kelvins of the heat engine (or hot reservoir), TH and calculate a value for the other term be able to re-arrange the equation Understand the following concepts: o law of conservation of energy know the definition of the first law of thermodynamics in words as, the heat energy supplied to a system is equal to the increase in the internal energy of the system plus the work done by the system on its surroundings, well as the equation Q = ΔU + ΔW o ideal gas equation pV = NkT know that pV = NkT applies to molecules of a gas and N is the number of molecules and k is a constant called the Boltzmann constant be able to perform appropriate calculations remembering that T is in kelvins understand that the ideal gas equation pV = nRT applies to moles of a gas
understand the graphical representation of the idealised engine cycle o second law of thermodynamics know the second law of thermodynamics in terms of entropy and the direction in which heat energy moves understand it as a limiting factor in the efficiency of heat engines, i.e. know that it is not possible to convert thermal energy continuously into other useful forms of energy or work without at the same time transferring some of the thermal energy from a warmer body (heat engine) to a colder body (or surroundings) o heat engines, refrigerators and heat pumps understand the graphical representation of heat pump cycle understand the differences and similarities between the action of a heat engine, to include the Stirling engine, and a heat pump understand the action of a refrigerator as a reverse heat engine/pump know that under normal circumstances, heat only flows from high temperatures to low temperatures. In order to move heat from a low temperature environment to a high temperature environment, work needs to be done (or energy needs to be transferred) o maximum theoretical coefficient of performance (COP) understand that the COP for a heat pump or engine is the ratio of the energy transferred for heating to the input energy used in the process know that higher the COPs equate to lower operating costs know that COP = Q/W where Q is the thermal energy supplied or removed from the system and W is the work done on or by the system or: COP = Thot/ ( Thot – Tcold) Understand the changes of state of substances used in domestic and industrial processes: o transfer of energy producing temperature change or changes of state, thermal capacity, thermal equilibrium understand the difference between the specific heat capacity of a substance and the thermal (heat) capacity of an object or system and the units of measurement of each o specific heat capacity from ( Q = mc ∆ T ) ^ understand how to experimentally determine the SHC of a solid, e.g. a metal such as aluminium and a liquid such as water be able to substitute values for any three of thermal energy supplied/given out, Q or mass, m or specific heat capacity, c or temperature change, ∆ T into the equation ( Q = mc ∆ T ) and calculate a value for the remaining term be able to re-arrange the equation
o specific latent heat from ( Q = mL ), fusion, vapourisation, condensation understand how to experimentally determine the SLH of fusion or vapourisation, of water and other common substances understand fusion, vaporisation and condensation on a molecular level in terms of the arrangement of particles, the forces between the particles and the distance of separation of particles in solids, liquids and gases be able to substitute values for any two of thermal energy supplied/given out, Q or mass, m or specific latent heat, L into the equation ( Q = mL ) and calculate a value for the remaining term be able to re-arrange the equation
C2 Materials in domestic and industrial applications
Understand the following concepts and apply them in domestic and industrial applications: o elasticity understand the properties of an elastic material in the elastic region of a stress/strain or Force /extension graph o stress-strain curves be able to interpret curves and be able to identify key points and regions including: the limit of proportionality, the elastic limit, the yield point and breaking point be able to recognise curves for different materials, to include: iron, copper, nylon, glass, and rubber/elastic bands understand the molecular behaviour of the material in the Hooke’s law region, to include: the limit of proportionality, the elastic limit, the yield strength/point and breaking/fracture point o elastic limit know that the elastic limit can be referred to as the point beyond which the material will not return to its original shape. The elastic limit is just beyond the limit of the Hooke’s law region (region of proportionality) for material o strength understand the difference between the strength of a material and how strong it is o yield point understand what happens at the molecular level at the yield point, in terms of slip planes and the way the material behaves at the yield point o plastic deformation understand the properties of plastic deformation in the region beyond the yield point of a stress/strain or Force /extension graph
o tensile/compressive stress (Newton per metre squared (Nm-2)) know that the pascal (Pa) is equivalent to the Newton per metre squared (Nm-2) and so be able to use Pascal (Pa) as a unit of tensile/compressive stress o tensile/compressive strain (no units) (^) know that strain is a ratio is a ratio of two distances and so has no units o Young’s modulus (Newton per metre squared (Nm-2)) know that Young’s modulus can be only calculated from the gradient in the Hooke’s Law region/ region of proportionality of a stress/strain graph know how the value can be experimentally determined Understand the following definitions: o density p = m / v ^ be able to convert between units used to measure density, for example: gm to kg and cm^3 to m^3 be able to substitute values for any two of density, ρ or mass, m or volume, V into the equation ρ = m / v and calculate a value for the remaining term be able to re-arrange the equation be able to describe how to measure the density of solids and liquids o tensile/compressive stress = F / A ^ know and use the terms compressive and tensile to describe the stress placed on materials understand the direction in which tensile/compressive stress is applied to produce a tensile/compressive strain be able to substitute values for any two of tensile/compressive stress or force (load), F or (cross-sectional) area, A into the equation tensile/compressive stress = F / A and calculate a value for the remaining term be able to re-arrange the equation o tensile/compressive strain = ∆ x / L ^ understand that strain is a dimensionless quantity as it is the ratio of two distances understand that tensile/compressive strain is linear because of the direction of the stress applied be able to substitute values for any two of tensile/compressive strain or extension (stretch) of the material, ∆ x or original length of material, L into the equation: tensile/compressive strain = ∆ x / L and calculate a value for the remaining term be able to re-arrange the equation
o Young’s modulus E = stress / strain ^ be able to use the equations for the terms: o F / A for stress o ∆x / L for strain be able to use the equation E = F.L/ A.∆x be able to determine Young’s modulus, E from the gradient of a stress/strain curve o Hooke’s law F = k ∆ x be able to substitute values for any two of force (load), F or stiffness constant ( constant of proportionality), k or extension (stretch) of the material, ∆ x into the equation F = k ∆ x and calculate a value for the remaining term be able to re-arrange the equation know that in the region of proportionality the stiffness constant, k determines the slope or gradient of a (force) load/extension graph o work done in stretching/compressing a wire/spring = ½ F ∆ x = ½ k( ∆ x )^2 be able to substitute values for any two of work done, W or force (load), F or extension (stretch) of the material, ∆ x into the equation W = ½ F ∆ x and calculate a value for the remaining term be able to re-arrange the equation be able to substitute values for any two of work done, W or stiffness constant ( constant of proportionality), k or extension (stretch) of the material, ∆ x into the equation W = ½ k( ∆ x)^2 and calculate a value for the remaining term be able to re-arrange the equation be able to calculate work done in stretching a wire/spring by determining the area below a load/extension graph
C3 Fluids in motion
Understand the following concepts and apply them in industrial and domestic situations: o fluid flow patterns, streamline and turbulent flow know that a smooth or steady flow is also referred to as laminar flow the streamlines are smooth know that in turbulent flow streamlines cross and mix know that a streamline shows the direction of flow of a fluid
o when an incompressible, smoothly flowing fluid gains speed, internal pressure of the fluid decreases and when the fluid’s speed decreases, internal pressure increases Learners do not need to know or use the equation relating to the principle
