CORE Physics (Short Course) - 9223 OxfordAQA

Energy Transfers And Particle Motion

Bayani Gaba-gaba

Walk out of a warm house on a frosty morning and take hold of the metal gate latch, then rest your other hand on the wooden gatepost beside it. The latch is painful. The post is merely chilly. Both have stood in the same air all night, so a thermometer pressed against either one would give you the same reading to within a fraction of a degree. Your hand is not measuring their temperature at all. It is measuring how quickly each of them is emptying your fingers of energy, and on that measure the two are nowhere near each other.

This lesson is about rate: not how much energy an object holds, but how fast it moves and what governs the speed. You will trace energy through a solid by vibration and by free electrons, watch a fluid carry its own energy upwards because heating has made it thinner, calculate a surface area to volume ratio and use it to explain both the fins on a motorcycle engine and the enormous ears of a desert fox, and finish with the two faces of thermal expansion: the one that buckles a bridge and the one that switches an iron off.

Manufura

  1. Energy may be transferred by conduction and convection. Students should be able to explain, in terms of particles, how these energy transfers take place. They should understand in simple terms how the arrangement and movement of particles determine whether a material is a conductor or an insulator and understand the role of free electrons in conduction through a metal. They should be able to use the idea of particles moving apart to make convection.
  2. The rate at which an object transfers energy by heating depends on: its surface area and volume; the material from which the object is made; the nature of the surface with which the object is in contact. Students should be able to explain the design of devices in terms of energy transfer, for example cooling fins, and should be able to explain animal adaptations in terms of energy transfer, for example relative ear size of animals in cold and warm climates.
  3. The bigger the temperature difference between an object and its surroundings, the faster the rate at which energy is transferred by heating.
  4. Most substances expand when heated. Students should understand that the expansion of substances on heating may be a hazard (for example, the expansion of roofs and bridges) or useful (for example, the bi-metallic strip thermostat).

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Takardar Darasi

Your skin has no sense that reports temperature. What it reports is the rate at which energy leaves it or arrives in it, which is a different quantity altogether. Grip a metal latch at 2 °C and energy pours out of your fingers, because the metal accepts it as fast as your hand can supply it and carries it away into the gate. Grip a wooden post at the same 2 °C and the wood takes energy from a thin surface layer, warms there, and then more or less stops. The temperature is a tie. The rate is not close.

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Nazarin Darasi

Barka da kammala darasi akan Energy Transfers And Particle Motion. Yanzu da kuka bincika mahimman raayoyi da raayoyi, lokaci yayi da zaku gwada ilimin ku. Wannan sashe yana ba da ayyuka iri-iri Tambayoyin da aka tsara don ƙarfafa fahimtar ku da kuma taimaka muku auna fahimtar ku game da kayan.

Za ka gamu da haɗe-haɗen nau'ikan tambayoyi, ciki har da tambayoyin zaɓi da yawa, tambayoyin gajeren amsa, da tambayoyin rubutu. Kowace tambaya an ƙirƙira ta da kyau don auna fannoni daban-daban na iliminka da ƙwarewar tunani mai zurfi.

Yi wannan ɓangaren na kimantawa a matsayin wata dama don ƙarfafa fahimtarka kan batun kuma don gano duk wani yanki da kake buƙatar ƙarin karatu. Kada ka yanke ƙauna da duk wani ƙalubale da ka fuskanta; maimakon haka, ka kallesu a matsayin damar haɓaka da ingantawa.

  1. Why is copper a much better thermal conductor than plastic? A. The particles in copper are further apart B. Copper contains free electrons that can move through it and transfer energy by collision C. Copper particles are heavier, so they vibrate more slowly D. Copper allows convection currents to form inside it Answer: B
  2. A solid metal cube has sides of 3.0 cm. What is its surface area to volume ratio? A. 0.50 per cm B. 2.0 per cm C. 27 per cm D. 54 per cm Answer: B
  3. Warm water at the bottom of a beaker rises. Why? A. Its mass decreases when it is heated B. Its particles expand when they are heated C. It expands, so its density becomes lower than that of the water around it D. Free electrons carry it upwards Answer: C
  4. A mug of hot tea is left standing in a room. Why does its rate of cooling get slower as time passes? A. The tea has less energy left, so it cannot transfer energy as quickly B. The temperature difference between the tea and the room gets smaller C. The surface area of the tea gets smaller as it cools D. The mug becomes a worse conductor once it has cooled Answer: B
  5. A bimetallic strip made of copper joined to iron is heated. Which statement is correct? A. The strip stays straight because the two metals are joined B. The strip bends with the copper on the inside of the curve C. The strip bends with the copper on the outside of the curve, because copper expands more than iron D. The strip breaks apart because the two metals expand by different amounts Answer: C

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