Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 1: Problem 9

On a hot summer day, a student turns his fan on when he leaves his room in the morning. When he returns in the evening, will his room be warmer or cooler than the neighboring rooms? Why? Assume all the doors and windows are kept closed.

Short Answer

Expert verified
Answer: The fan running all day in a closed room makes the room warmer compared to neighboring rooms with no fans due to the heat generated by the fan's inefficiencies. However, it can make the room feel cooler if someone is present because of the increased air circulation.

Step by step solution

01

Understand the heat exchange between the room and the surroundings

Since the doors and windows are closed, the exchange of heat with the surroundings will be minimal. In the closed room, the only significant heat exchange will happen due to the fan, which takes in electrical energy and then converts it into mechanical work and heat.
02

Analyze the work done by the fan

The fan's job is to circulate air within the room, which can make the room feel cooler because of increased air movement across the skin, allowing better heat transfer from the body to air. However, the fan itself doesn't lower the room's temperature.
03

Analyze the heat produced by the fan

Any electrical appliance, including a fan, generates heat as it works. This is because it converts electrical energy into the mechanical work of circulating air, and some of that energy unavoidably gets transformed into heat due to electrical and mechanical inefficiencies.
04

Compare the room temperature with neighboring rooms

The fan stays on throughout the day, continually generating and releasing heat into the room while making some air circulation. In contrast, assuming the neighboring rooms have no electrical appliances generating heat, they lack both additional heat from appliances and air circulation.
05

Determine whether the room will be warmer or cooler

Given that the fan generates heat throughout the day due to its inefficiencies, it will make the room warmer compared to the neighboring rooms, despite making it feel cooler if someone is in the room due to air circulation.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

A flat-plate solar collector is used to heat water by having water flow through tubes attached at the back of the thin solar absorber plate. The absorber plate has a surface area of \(2 \mathrm{~m}^{2}\) with emissivity and absorptivity of \(0.9\). The surface temperature of the absorber is \(35^{\circ} \mathrm{C}\), and solar radiation is incident on the absorber at \(500 \mathrm{~W} / \mathrm{m}^{2}\) with a surrounding temperature of \(0^{\circ} \mathrm{C}\). Convection heat transfer coefficient at the absorber surface is \(5 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\), while the ambient temperature is \(25^{\circ} \mathrm{C}\). Net heat rate absorbed by the solar collector heats the water from an inlet temperature \(\left(T_{\text {in }}\right)\) to an outlet temperature \(\left(T_{\text {out }}\right)\). If the water flow rate is \(5 \mathrm{~g} / \mathrm{s}\) with a specific heat of \(4.2 \mathrm{~kJ} / \mathrm{kg} \cdot \mathrm{K}\), determine the temperature rise of the water.

What is a blackbody? How do real bodies differ from blackbodies?

Heat treatment is common in processing of semiconductor material. A 200-mm- diameter silicon wafer with thickness of \(725 \mu \mathrm{m}\) is being heat treated in a vacuum chamber by infrared heater. The surrounding walls of the chamber have a uniform temperature of \(310 \mathrm{~K}\). The infrared heater provides an incident radiation flux of \(200 \mathrm{~kW} / \mathrm{m}^{2}\) on the upper surface of the wafer, and the emissivity and absorptivity of the wafer surface are \(0.70\). Using a pyrometer, the lower surface temperature of the wafer is measured to be \(1000 \mathrm{~K}\). Assuming there is no radiation exchange between the lower surface of the wafer and the surroundings, determine the upper surface temperature of the wafer. (Note: A pyrometer is a non-contacting device that intercepts and measures thermal radiation. This device can be used to determine the temperature of an object's surface.)

What is asymmetric thermal radiation? How does it cause thermal discomfort in the occupants of a room?

An electric heater with the total surface area of \(0.25 \mathrm{~m}^{2}\) and emissivity \(0.75\) is in a room where the air has a temperature of \(20^{\circ} \mathrm{C}\) and the walls are at \(10^{\circ} \mathrm{C}\). When the heater consumes \(500 \mathrm{~W}\) of electric power, its surface has a steady temperature of \(120^{\circ} \mathrm{C}\). Determine the temperature of the heater surface when it consumes \(700 \mathrm{~W}\). Solve the problem (a) assuming negligible radiation and (b) taking radiation into consideration. Based on your results, comment on the assumption made in part ( \(a\) ).
See all solutions

Recommended explanations on Physics Textbooks

Geometrical and Physical Optics

Read Explanation

Scientific Method Physics

Read Explanation

Famous Physicists

Read Explanation

Magnetism

Read Explanation

Turning Points in Physics

Read Explanation

Oscillations

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free