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HEATING & COOLING

HEATING & COOLING. Unit 1 - SPC. HOT. COLD. APPLE PIE…. Which cools fastest…filling or crust?. LESSON OBJECTIVES:. Appreciate that different materials heat up and cool down at different rates, depending upon their Specific Heat Capacity.

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HEATING & COOLING

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  1. HEATING&COOLING Unit 1 - SPC HOT COLD

  2. APPLE PIE… Which cools fastest…filling or crust?

  3. LESSON OBJECTIVES: Appreciate that different materials heat up and cool down at different rates, depending upon their Specific Heat Capacity. Recognise the terms in the equation for heat energy transfer. Investigate how to measure the Specific Heat Capacity of a material.

  4. E = m x g x h When we move an object up or down we cause it to gain or lose potential energy: Energy change (J) Mass (kg) Gravitational field strength for a planet (N/kg) Height difference (m)

  5. E = m x c x  When we heat an object up or cool it down we cause it to gain or lose heat energy: Energy change (J) Mass (kg) Specific Heat Capacity for a material (J/kg/C) Temperature difference (C)

  6. The Specific Heat Capacity essentially measures how much energy 1kg of a material must gain/lose to go up/down in temperature by 1C.

  7. EXAMPLE 1: How much energy is needed to heat 2kg of oil up by 25C, if the SHC of the oil is 1000J/kg/ C? SOLUTION: E = mc E = 2 x 1000 x 25 E = 50,000J

  8. EXAMPLE 2: Bartonium has an SHC of 200J/kg/ C. A mass of 3kg is warmed up by a 50W heater switched on for 5 minutes. What is the temperature rise? SOLUTION: E = mc  Pt = mc  50W x 300s = 3kg x 200 x  •  = 15,000 / 600   = 25 C

  9. EXPERIMENT: • What is the Specific Heat Capacity (c) of an aluminium block? • How accurate is the experiment? Think about limitations, errors, modifications, etc. Electrical energy (IN): E = V x I x t Heat energy (OUT): E = m x c x 

  10. EXPERIMENT: Why is it poor? • Not all of the heater is inside the block • The heater is not very efficient (only 25% or less?) • The aluminium block is not insulated • Heat does not travel instantly or evenly through the block • Powerpack voltage is not correct (r) • Heater will take time to warm up NB – Our measurements are probably quite precise but for all of the reasons above our answer will not be exact or accurate. Specific Heat Capacity of aluminium = 650 J/kg/C.

  11. LESSON OUTCOMES: Recall & use the equation E = mc for objects that are heating up or cooling down. Apply this equation to everyday situations. Describe how Specific Heat Capacity can be measured.

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