PHYSC100- 2OA Lab4-Mechnical Equivalence of Heat Specific Heat PDF

Preview

Summary

Lab4-Mechnical Equivalence of Heat Specific Heat...

Description

Name: Shereen Bakshi

ID: 1541605

Date: 10/04/2020

Lab 4 – Mechanical equivalence of heat/specific heat Follow this link to the simulator which will be used for this lab and click the play button: http://phet.colorado.edu/en/simulation/energy-forms-and-changes Section 1: Mechanical equivalence of heat In this simulation, you will be able to “see” several different forms of energy and the changes (transfers) that can occur between them. You are also able to work with a system where you can manipulate the energy input, observe the process of electrical energy generation and manipulate the output. Click on the “Energy Systems” tab. We will do section 1 of the lab here. Be sure to click the “Energy Symbols” box so the different types of energy will be visible throughout the process.

Getting Familiar With The Options Please experiment with the different source, generation and output options – there are many combinations to play with – then complete the questions below. 1. Which energy sources (input) can cause the turbine (wooden wheel) to spin and generate electrical energy? Bike, kettle, tap 2. Which energy sources (input) cause the solar panels to generate electrical energy? sun 3. Which energy output objects work with the turbine? All of them 4. Which energy output objects work with the solar panels? All of them 5. Specify what happens (in terms of increases of decreases) to the amount of electrical energy that is generated when the:

a) The flow of water from the tap is increased? b) The amount of cloud cover is increased? c) The heat setting on the kettle is moved from low to high? d) The girl increases her rate of pedaling?

Answer More electrical energy is generated Less electrical energy is generated More electrical energy is generated More electrical energy is generated

e) Explain why the cyclist must be fed in order to continue to pedal? The cyclist must be fed to gain energy which in turn is required for pedaling. f) If the cyclist eats 2000 kcal, how much energy in Joules is she then able to expend as kinetic energy? (Assume all energy from the food is converted to kinetic energy, 1 cal = 4.186 J).

8372J g) The law of conservation of energy states: The law of conservation of energy states that energy can neither be created nor destroyed only converted from one form of energy to another. This means that a system always has the same amount of energy, unless it's added from the outside.

Exploring Energy Transfer Set up your system as shown in the picture. Let it run for a while to reach a steady state and then complete the sentences using the energy symbols to help you “see” the flow of the energy within each system. HINT: Make sure to check the Energy Symbols box. Use the color of the “E” boxes to know what form the energy is. h) Turbine Moved by Medium Water Flow from Faucet With A Water Heater System

In this system, kinetic energy from the moving water of the faucet turns the turbine. The mechanical energy of the spinning turbine generates electrical energy which is transformed into thermal energy that causes the temperature of the water to increase. The water then becomes steam and gives off more thermal energy into the atmosphere.

i)

Solar Panel in No Cloud Cover With An Incandescent Light Bulb System

In this system, light energy from the sunlight causes the solar panel to create electrical energy which flows into the incandescent light bulb. In the light bulb, the electrical energy is transformed into two different types of energy: light energy and thermal energy. j)

Turbine Moved by Steam from Medium Heat Kettle With A Fan

In this system, thermal energy from the flames of the fire transfer energy to the kettle causing the liquid to become steam. The thermal energy of the steam spins the turbine (mechanical energy) which generates electrical energy that is used to operate the fan. The moving electric motor and the spinning fan blades are a form of mechanical energy.

After running for a while, the fan becomes

hot to the touch, and ever so often releases thermal energy into the air. *Note* Another form of energy is released from the kettle. What is it? Mechanical k) Turbine Moved by Cyclist Pedaling at Medium Speed With A Fluorescent Light Bulb System

In this system, chemical energy from the cyclist is converted to mostly mechanical energy and a small amount of thermal energy. The mechanical energy from the turning bicycle wheel spins the turbine which generates electrical energy. The fluorescent light bulb converts this energy into two new forms: a lot of light energy and very little thermal energy. l)

Switch out the fluorescent bulb (curly one) with the incandescent bulb (rounded) and observe the energy output. What do you notice about the difference in the energy and output of these two bulbs? The incandescent bulb produces more heat than the fluorescent bulb. In your opinion, which light bulb is more efficient? In my opinion, Fluorescent bulb will be more efficient.

Explain how you know this. From the law of conservation of energy, we know that the system always has the same amount of energy. The total energy in this case is the light energy added with the thermal energy whereas, what we need more is the light energy and since fluorescent bulb gives out more of light energy and lesser thermal energy, this suggests that its more efficient. m) What common form of energy (not including kinetic or potential) is not included in the “Energy Symbols” key that would normally be present in these examples? Sound energy n) Look carefully at each of the four systems shown above. Thinking about energy conversions, identify (list) at least three different places where this form of energy (sound) should be “produced”. Falling water from the tap, pedaling bicycyle, kettle, turbine, fan o) In some areas it is common to use windmills to pump water from underground to fill a tank for drinking water. The wind causes the turbine blades to spin, rotating a shaft, which is transferred through some gears to operate a pump, which pumps water up from deep below the ground to fill an above ground tank. Identify the energy conversions happening at each step below. a) Wind blows (kinetic energy) b) causing the turbine to turn, rotating shaft works pump (mechanical energy) c) Motion of water moving up from well (kinetic energy) d) Water in tank which is positioned 2 metres above the ground level (gravitational potential energy) Section 2: Specific heat Go into the ‘Intro’ part of the simulation via the button at the bottom of the screen. Place the Iron on one of the stands and a thermometer on both the Iron and the water as below.

Hold the slider to heat the Iron block until the thermometer attached to the Iron is reading its maximum. Transfer the Iron block into the water and watch both thermometers until the ready a steady state (stop changing). a) How do the initial temperatures of the Iron and water compare? Iron is at the maximum temperature and water is near the first bar. b) How do the final temperatures of the Iron and water compare? They are the same. c) On the same diagram, sketch the evolution of the temperature of both the Iron block and the water with time (note in a sketch you don’t need numbers but axis should be labelled and curves representing the temperature should be included).

d) If energy in a closed system must be conserved then the heat that leaves the metal upon cooling must be equal to the heat added to the water. The heat Q, can be calculated through 𝑄 = 𝑚𝑐∆𝑇, where m is mass of that substance [kg], c is the specific heat of that material [J/kgK] (Joules per kg Kelvin) and ∆𝑇 = 𝑇𝑓 − 𝑇𝑖 . Material Iron Water m [kg] 0.10 0.25 c [J/kgK] 460 4186 Tf [K] 313 313 Ti [K] ? 288 Using the information of the experiment given in the table, find the initial temperature of Iron in Kelvin (show your working). Q=mc Q (water)= 0.25 X 4186 X 25 = 26162.5 Q=mc T= Q/mc =26162.5/ (.1 X 460) = 568.75 T (i)= 568.75 + 313= 881.75 e) What is this value in degrees Celcius? 608.6 f) What assumptions are made in this calculation? (Hint: think about losses) No energy is lost during the process. g) Given the specific heat capacity of brick is 841 J/kgK. For the same mass of material and the same experimental set up used previously, do you expect the brick to heat faster or slower than Iron? Explain your answer. The specific heat of iron being lower than the specific heat of brick. Therefore, it requires less heat per unit mass to create a greater change in temperature. Thus the iron heats faster. h) Does the simulator agree? Why not? (Hint: think about the relative densities of the two materials). No, since Iron is a lot denser than brick and hence takes slightly longer to heat up....