PHY 113 C General Physics I 11 AM

  • Slides: 33
Download presentation
PHY 113 C General Physics I 11 AM – 12: 15 PM MWF Olin

PHY 113 C General Physics I 11 AM – 12: 15 PM MWF Olin 101 1. 2. 3. 4. 5. Plan for Lecture 24: Review: Chapters 17 -18, 14, 19 -22 Sound; Doppler effect & standing waves Physics of fluids; pressure, buoyant force, Bernoulli’s equation Temperature & heat & ideal gas law First law of thermodynamics Cycles and their efficiency 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 1

11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 2

11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 2

Comment about Exam 3: • Part I – take home portion (1 problem): available

Comment about Exam 3: • Part I – take home portion (1 problem): available at end of class today -- 11/21/2013; must be turned in before part II • Part II – in-class portion (3 problems) -Tuesday 11/26/2013 • Some special arrangements for early exams have been arranged by prior agreement • Of course, all sections of the exam are to be taken under the guidelines of the honor code 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 3

iclicker question How are you doing on preparing your equation sheet for Exam 3?

iclicker question How are you doing on preparing your equation sheet for Exam 3? A. It is completed B. It is almost completed C. I am in a panic because there are too many equations this time 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 4

Webassign – Assignment #21 The work done by an engine equals one-fourth the energy

Webassign – Assignment #21 The work done by an engine equals one-fourth the energy it absorbs from a reservoir. (a) What is its thermal efficiency? (b) What fraction of the energy absorbed is expelled to the cold reservoir? 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 5

Webassign – Assignment #21 What is the coefficient of performance of a refrigerator that

Webassign – Assignment #21 What is the coefficient of performance of a refrigerator that operates with Carnot efficiency between temperatures -3. 00°C and +27. 0°C? 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 6

Webassign – Assignment #21 A gasoline engine has a compression ratio of 6. 00

Webassign – Assignment #21 A gasoline engine has a compression ratio of 6. 00 and uses a gas for which γ = 1. 40. (a) What is the efficiency of the engine if it operates in an idealized Otto cycle? (b) If the actual efficiency is 16. 0%, what fraction of the fuel is wasted as a result of friction and energy losses by heat that could by avoided in a reversible engine? (Assume complete combustion of the air-fuel mixture. ) fraction lost= ideal-actual=0. 51 -0. 16=0. 35 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 7

Webassign – Assignment #21 An idealized diesel engine operates in a cycle known as

Webassign – Assignment #21 An idealized diesel engine operates in a cycle known as the air-standard diesel cycle shown in the figure below. Fuel is sprayed into the cylinder at the point of maximum compression, B. Combustion occurs during the expansion B → C, which is modeled as an isobaric process. Show that the efficiency of an engine operating in this idealized diesel cycle is given by the following expression. 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 8

Comment on adiabatic process (Q=0) -- 11/21/2013 PHY 113 C Fall 2013 -- Lecture

Comment on adiabatic process (Q=0) -- 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 9

Comment on adiabatic process (Q=0) -- continued 11/21/2013 PHY 113 C Fall 2013 --

Comment on adiabatic process (Q=0) -- continued 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 10

Comment on adiabatic process (Q=0) – continued Suppose you were asked to calculate the

Comment on adiabatic process (Q=0) – continued Suppose you were asked to calculate the final pressure for an expansion process where Vi/Vf=1/10 when Pi=1 atm. and when g=1. 3? 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 11

Review of main ideas from Chapters: 17 -18 – Sound waves 14 -- Physics

Review of main ideas from Chapters: 17 -18 – Sound waves 14 -- Physics of fluids 19 -22 – Temperature, heat, thermodynamics 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 12

Physics of sound waves Sound waves are described by the wave equation time position

Physics of sound waves Sound waves are described by the wave equation time position Change of average air density or pressure 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 13

Standing waves. Two sinusoidal waves, same amplitude, same f, but opposite directions Standing wave:

Standing waves. Two sinusoidal waves, same amplitude, same f, but opposite directions Standing wave: 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 14

Standing waves between reflecting walls 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24

Standing waves between reflecting walls 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 15

Doppler effect 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 16

Doppler effect 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 16

toward away Relative velocity of source toward observer 11/21/2013 PHY 113 C Fall 2013

toward away Relative velocity of source toward observer 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 17

Typical question concerning Doppler effect: A driver travels northbound on a highway at a

Typical question concerning Doppler effect: A driver travels northbound on a highway at a speed of 30. 0 m/s. A police car, traveling southbound at a speed of 34. 0 m/s, approaches with its siren producing sound at a frequency of 2500 Hz. (a) What frequency does the driver observe as the police car approaches? (b) What frequency does the driver detect after the police car passes him? 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 18

The physics of fluids. • Fluids include liquids (usually “incompressible) and gases (highly “compressible”).

The physics of fluids. • Fluids include liquids (usually “incompressible) and gases (highly “compressible”). • Fluids obey Newton’s equations of motion, but because they move within their containers, the application of Newton’s laws to fluids introduces some new forms. ØPressure: P=force/area 1 (N/m 2) = 1 Pascal ØDensity: r =mass/volume 1 kg/m 3 = 0. 001 gm/ml 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 19

General relationship between P and r: Buoyant force for fluid acting on a solid:

General relationship between P and r: Buoyant force for fluid acting on a solid: FB=rfluid. Vdisplacedg A Dy mg 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 20

Bernoulli’s equation: 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 21

Bernoulli’s equation: 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 21

Bernoulli’s equation: 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 22

Bernoulli’s equation: 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 22

Webassign questions on fluids (Assignment #17) A hypodermic syringe contains a medicine with the

Webassign questions on fluids (Assignment #17) A hypodermic syringe contains a medicine with the density of water (see figure below). The barrel of the syringe has a crosssectional area A = 2. 40 10 -5 m 2, and the needle has a crosssectional area a = 1. 00 10 -8 m 2. In the absence of a force on the plunger, the pressure everywhere is 1. 00 atm. A force of magnitude 2. 65 N acts on the plunger, making medicine squirt horizontally from the needle. Determine the speed of the medicine as it leaves the needle's tip. 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 23

Notion of temperature: Effects of temperature on materials – continued -ideal gas “law” (thanks

Notion of temperature: Effects of temperature on materials – continued -ideal gas “law” (thanks to Robert Boyle (16271691), Jacques Charles (1746 -1823), and Gay. Lussac (1778 -1850) 8. 314 J/(mol K) temperature in K volume in m 3 # of moles pressure in Pascals 1 mole corresponds to 6. 022 x 1023 molecules 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 24

Notion of heat Heat can be used to change temperature: Heat capacity: C =

Notion of heat Heat can be used to change temperature: Heat capacity: C = amount of heat which must be added to the “system” to raise its temperature by 1 K (or 1 o C). Q = C DT Heat capacity per mass: C=mc Heat capacity per mole (for ideal gas): C=n. Cv C=n. Cp 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 25

Some typical specific heats Material Water (15 o. C) Ice (-10 o. C) Steam

Some typical specific heats Material Water (15 o. C) Ice (-10 o. C) Steam (100 o. C) Wood Aluminum Iron Gold 11/21/2013 J/(kg·o. C) 4186 2220 2010 1700 900 448 129 PHY 113 C Fall 2013 -- Lecture 24 cal/(g·o. C) 1. 00 0. 53 0. 48 0. 41 0. 22 0. 11 0. 03 26

Heat and changes in phase of materials Example: A plot of temperature versus Q

Heat and changes in phase of materials Example: A plot of temperature versus Q added to 1 g = 0. 001 kg of ice (initially at T=-30 o. C) 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 27

Typical question concerning heat: Suppose you have a well-insulated cup of hot coffee (m=0.

Typical question concerning heat: Suppose you have a well-insulated cup of hot coffee (m=0. 3 kg, T=100 o. C) to which you add 0. 3 kg of ice (at 0 o. C). When your cup comes to equilibrium, what will be the temperature of the coffee? 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 28

Important equations for macroscopic and microscopic descriptions of thermodynamic properties of matter 11/21/2013 PHY

Important equations for macroscopic and microscopic descriptions of thermodynamic properties of matter 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 29

Question from previous exam: 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 30

Question from previous exam: 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 30

FB mg T 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 31

FB mg T 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 31

Question from previous exam: 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 32

Question from previous exam: 11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 32

11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 33

11/21/2013 PHY 113 C Fall 2013 -- Lecture 24 33