Worksheet4-Heat+Transfer-2018-vfinal.pdf - Physics 100...

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Physics 100 Worksheet #4 Sections 13.1, 15.1, 14.1, 14.4, 14.5: Thermodynamics Name:_____________________________ Student No. : ____________________ Section: ________ Instructions: 1. Bring this worksheet with you to class until completed. Keep it to help you study for exams.. 2. Form small groups of 2 to 4 students. Discuss all answers with your group. Ask your TA or lecturer for hints if required. Double-check your answers with a TA when done. ____________________________________________________________________________________ Introduction to the First Law of Thermodynamics So far we have looked at mechanical work and energy. We have then expanded our ideas to energy transformation processes and efficiency. In many of these cases, some fraction of energy is transformed into thermal energy and then lost from the system as heat. We will look at heat transfer and find out how thermal energy is ‘lost’ to the environment. Let’s start with a general principle: work and heat change the internal energy of a system . Both work and heat are energy transfers and have the unit joule (you can think of these as ‘energy in motion’) . Positive and negative signs indicate that energy is transferred into (+) our out of (-) the system. Q14.1 Consider the food in a food processor or blender. When you switch it on: Since both heat and work are energy transfers, we should include both in our energy balance. Expanding our model to include all the types of energy our system can have, we can write: ∆𝐸 = ∆𝐸 mech + ∆𝐸 th + ∆𝐸 chem + ⋯ = 𝑄 net + 𝑊 net Here E th is the thermal energy of the system, which is proportional to the temperature T, and E chem is the chemical energy of the system . The … allows for other possible types of energy (like nuclear energy). What happens to the temperature of the food? Why? (In terms of work and heat, what do the blades do to the food?)
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