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class="col-md-9" id="main-column"> <h1 class="page_title"> Heat transfer <a href="#" class="mark-page-favorite pull-right" data-pid="256" title="Mark as favorite" onclick="return false;"><i class="fa fa-star-o"></i></a> </h1> <ol class="breadcrumb"> <li><a href="../../../physics.html"><i class="fa fa-home"></i></a><i class="fa fa-fw fa-chevron-right divider"></i></li><li><a href="../252/thermal.html">Thermal</a><i class="fa fa-fw fa-chevron-right divider"></i></li><li><a href="../254/thermal-concepts.html">Thermal concepts</a><i class="fa fa-fw fa-chevron-right divider"></i></li><li><span class="gray">Heat transfer</span></li> <span class="pull-right" style="color: #555" title="Suggested study time: 30 minutes"><i class="fa fa-clock-o"></i> 30&apos;</span> </ol> <article id="main-article"> <p><img alt="" src="../../thermal/hot-spring.jpg" style="width: 250px; height: 167px; float: left;">Whether you want to prevent heat from escaping,&nbsp;cook something more quickly&nbsp;or answer an exam question, you need to know the processes of heat transfer:</p> <ul style="margin-left: 240px;"> <li>conduction</li> <li>convection</li> <li>radiation</li> </ul> <p>It&#39;s also worth a look at the&nbsp;<a href="../254/thermal-concepts.html" title="Thermal concepts">Thermal concepts</a>&nbsp;page for information about&nbsp;<em>evaporation</em>.&nbsp;</p> <hr class="hidden-separator"> <div class="panel panel-has-colored-body panel-purple"> <div class="panel-heading"><a class="expander" href="#"><span class="fa fa-plus"></span></a> <div> <p>Summary</p> </div> </div> <div class="panel-body"> <div> <div class="panel panel-has-colored-body panel-has-border panel-purple"> <div class="panel-heading"><a class="expander" href="#"><span class="fa fa-plus"></span></a> <div> <p>Conduction</p> </div> </div> <div class="panel-body"> <div> <p>While all matter is capable of allowing heat transfer by <em>conduction</em>, it is fastest in solids, particularly in metals with delocalised electrons.</p> <p><img class="sibico" src="../../../img/sibico/video.svg" style="height:1.25em;width: auto;vertical-align:text-bottom" title="Video">&nbsp;When the end of a solid bar is heated, the particles are made to vibrate more than before. The kinetic energy is&nbsp;passed from one molecule to the next along the rod by collisions.</p> <p>NB: Remember that all objects above absolute zero will have at least some kinetic energy in their particles.</p> <div class="video-embed vimeo"><iframe allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen="" mozallowfullscreen="" webkitallowfullscreen="" height="420" width="100%" src="https://player.vimeo.com/video/163663526"></iframe></div> </div> </div> <div class="panel-footer"> <div> <p>&nbsp;</p> </div> </div> </div> <div class="panel panel-has-colored-body panel-has-border panel-purple panel-expandable"> <div class="panel-heading"><a class="expander" href="#"><span class="fa fa-plus"></span></a> <div> <p>Convection</p> </div> </div> <div class="panel-body"> <div> <p><img class="sibico" src="../../../img/sibico/exam-style.svg" style="height:1.25em;width: auto;vertical-align:text-bottom" title="Exam-style question">&nbsp;<em>We don&#39;t ask you to memorise much in Phyiscs, but it&#39;s worth learning the key words for a good convection answer...</em></p> <p>When a <strong>fluid</strong> is heated, the molecules <strong>spread apart</strong>,&nbsp;causing it to be <strong>less dense</strong>. This less dense fluid&nbsp;<strong>rises</strong> into the surrounding cold fluid. This leaves a region of <strong>low pressure</strong>&nbsp;behind and so the cooler, denser fluid fills the gap, creating a <strong>convection current</strong>.</p> <div class="video-embed vimeo"><iframe allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen="" mozallowfullscreen="" webkitallowfullscreen="" height="420" width="100%" src="https://player.vimeo.com/video/163588703"></iframe></div> </div> </div> <div class="panel-footer"> <div> <p>&nbsp;</p> </div> </div> </div> <div class="panel panel-has-colored-body panel-has-border panel-purple panel-expandable"> <div class="panel-heading"><a class="expander" href="#"><span class="fa fa-plus"></span></a> <div> <p>Radiation</p> </div> </div> <div class="panel-body"> <div> <p><img alt="" src="../../thermal/charcoal.jpg" style="float: left; width: 219px; height: 80px;">Radiation is what you feel as you warm your hands in front of a fire.</p> <p>All objects with a temperature above absolute zero emit infrared radiation. Infrared radiation is a region of the electromagnetic spectrum, and so it travels at the speed of light through a vacuum (convenient for&nbsp;planet Earth!) as well as being able to pass through air and other matter.&nbsp;</p> <p><img class="sibico" src="../../../img/sibico/video.svg" style="height:1.25em;width: auto;vertical-align:text-bottom" title="Video">&nbsp;The amount of radiated heat depends upon the temperature of the source, it&#39;s colour and surface area. The rate of radiation absorbed by and emitted from&nbsp;black bodies is greater than silver ones (which are much better reflectors). Hot objects emit more radiation than cooler objects.</p> <hr class="hidden-separator"> <div class="video-embed vimeo"><iframe allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen="" mozallowfullscreen="" webkitallowfullscreen="" height="420" width="100%" src="https://player.vimeo.com/video/163734668"></iframe></div> </div> </div> <div class="panel-footer"> <div> <p>&nbsp;</p> </div> </div> </div> </div> </div> <div class="panel-footer"> <div>&nbsp;</div> </div> </div> <div class="panel panel-has-colored-body panel-green"> <div class="panel-heading"><a class="expander" href="#"><span class="fa fa-plus"></span></a> <div> <p>Test Yourself</p> </div> </div> <div class="panel-body"> <div> <p><em>Use quizzes&nbsp;to practise application of theory.</em>&nbsp;</p> <br><a class="btn btn-primary btn-block text-center" data-toggle="modal" href="#5cc8d3f9"><i class="fa fa-play"></i> START QUIZ!</a><div class="modal fade modal-slide-quiz" id="5cc8d3f9"> <div class="modal-dialog" style="width: 95vw; max-width: 960px"> <div class="modal-content"> <div class="modal-header slide-quiz-title"> <h4 class="modal-title" style="width: 100%;"> Change of state <strong class="q-number pull-right"> <span class="counter">1</span>/<span class="total">1</span> </strong> </h4> </div> <div class="modal-body p-xs-3"> <div class="slide-quiz" data-stats="6-62-256" style="opacity: 0"> <div class="exercise shadow-bottom"><div class="q-question"><p>When a solid changes to a liquid energy is required.</p><p>Which is the best description of where that energy goes.</p></div><div class="q-answer"><p><label class="radio"><input class="c" type="radio"> to increase the PE of the molecules</label></p><p><label class="radio"><input type="radio"> to increase the KE of the molecules</label></p><p><label class="radio"><input type="radio"> to allow the molecules to move further apart</label></p><p><label class="radio"><input type="radio"> to break the bonds between atoms</label></p></div><div class="q-explanation"><p>Chemists talk about breaking bonds we talk about increasing PE, it would also be bonds between the molecules rather than atoms but I&#39;d rather not get into that.</p><p>Temperature doesn&#39;t change so no change in KE</p><p>Water molecules actually get closer.</p></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div><div class="exercise shadow-bottom"><div class="q-question"><p>100g ice is melted at 0&deg;C in 5 minutes by an electric heater.</p><p>The latent heat of fusion of ice is approximately 3 x 10<sup>5</sup> Jkg<sup>-1</sup></p></div><div class="q-answer"><p>The amount of heat required to melt the ice = <input type="text" style="height: auto;" data-c="30"> <span class="review"></span> kJ</p><p>The power of the heater = <input type="text" style="height: auto;" data-c="100"> <span class="review"></span> W</p></div><div class="q-explanation"><p>Q = mL, P = Q/t careful with units</p></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div><div class="exercise shadow-bottom"><div class="q-question"><p>The temperature is measured as some water is boiled in a 2kW electric kettle.</p><p style="text-align: center;"><img alt="" src="../../images/lhq1.png" style="width: 340px; height: 292px;"></p><p>The latent heat of vaporisation of water is about 2 x 10<sup>6</sup> Jkg<sup>-1</sup></p></div><div class="q-answer"><p>Temperature T = <input type="text" style="height: auto;" data-c="100"> <span class="review"></span> &deg;C</p><p>The heat required to boil the water = <input type="text" style="height: auto;" data-c="2000"> <span class="review"></span> kJ</p><p>The mass of water = <input type="text" style="height: auto;" data-c="1"> <span class="review"></span> kg</p></div><div class="q-explanation"><p>Q = Pt<br>m=Q/L</p></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div><div class="exercise shadow-bottom"><div class="q-question"><p>If you get melted sugar on your skin it burns very badly.</p><p>Fill the gaps to give the explanation.</p><p>Word list: constant, energy, solid, liquid, temperature, release, state, power</p></div><div class="q-answer"><p>When sugar changes from <input type="text" style="height: auto;" data-c="liquid"> <span class="review"></span> to <input type="text" style="height: auto;" data-c="solid"> <span class="review"></span> it must release <input type="text" style="height: auto;" data-c="energy"> <span class="review"></span> , if in contact with your skin this <input type="text" style="height: auto;" data-c="energy"> <span class="review"></span> will be given to you. <input type="text" style="height: auto;" data-c="temperature"> <span class="review"></span> remains constant as the sugar changes <input type="text" style="height: auto;" data-c="state"> <span class="review"></span> so it remains at melting point until all the <input type="text" style="height: auto;" data-c="energy"> <span class="review"></span> is released. during this time the sugar will be damaging your skin.</p></div><div class="q-explanation"><p>It does too.</p></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div><div class="exercise shadow-bottom"><div class="q-question"><p>A type of salt is used to store solar energy collected in the day time so it can be used at night. The power station collects 1 MW. </p><p>The latent heat of fusion of the salt is 3 x 10<sup>6</sup> Jkg<sup>-1</sup></p></div><div class="q-answer"><p>The energy collected in 10 hours of sun light = <input type="text" style="height: auto;" data-c="36000"> <span class="review"></span> MJ (no commas)</p><p>The mass of salt melted in one day (10 hours of sunlight) = <input type="text" style="height: auto;" data-c="12000"> <span class="review"></span> kg</p></div><div class="q-explanation"><p>MJ is 10<sup>6</sup> J</p></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div> </div> </div> <div class="modal-footer slide-quiz-actions"> <div class=""> <div class="pull-left pull-xs-none mb-xs-3"> <button class="btn btn-default d-xs-none btn-prev"> <i class="fa fa-arrow-left"></i>&nbsp;&nbsp;Prev </button> </div> <div class="pull-right pull-xs-none"> <button class="btn btn-success btn-xs-block text-xs-center btn-results" style="display: none"> <i class="fa fa-bar-chart"></i> Check Results </button> <button class="btn btn-default d-xs-none btn-next"> Next&nbsp;&nbsp;<i class="fa fa-arrow-right"></i> </button> <button class="btn btn-default btn-xs-block text-xs-center btn-close" data-dismiss="modal" style="display: none"> Close </button> </div> </div> </div> </div> </div></div> </div> </div> <div class="panel-footer"> <div>&nbsp;</div> </div> </div> <div class="panel panel-has-colored-body panel-red"> <div class="panel-heading"><a class="expander" href="#"><span class="fa fa-plus"></span></a> <div> <p>Just for Fun</p> </div> </div> <div class="panel-body"> <div> <p>Consider a frozen chicken. To defrost the chicken, you have two options: placing it on the worktop as it is, or wrapping it in a woollen jumper. Which option will be the quicker?</p> <button class="btn btn-xs bg-turquoise showhider"><i class="fa fa-fw fa-plus"></i></button><section class="hiddenbox hidden">Although perhaps unexpected, wrapping the chicken in a jumper will actually slow the defrosting. The jumper is an insulator, which means that it reduces heat transfer by conduction in any direction. Its trapped air pockets also reduce&nbsp;the extent of convection near to the chicken. It&#39;s worth remembering that materials (like wool) do not know what to keep warm.</section> </div> </div> <div class="panel-footer"> <div>&nbsp;</div> </div> </div> <div class="page-container panel-self-assessment" data-id="256"> <div class="panel-heading">MY PROGRESS</div> <div class="panel-body understanding-rate"> <div class="msg"></div>  <label class="label-lg">Self-assessment</label><p>How much of <strong>Heat transfer</strong> have you understood?</p><div class="slider-container text-center"><div id="self-assessment-slider" class="sib-slider self-assessment " data-value="1" data-percentage=""></div></div>  <label class="label-lg">My notes</label> <textarea name="page-notes" class="form-control" rows="3" placeholder="Write your notes here..."></textarea> </div> <div class="panel-footer text-xs-center"> <span id="last-edited" class="mb-xs-3"> </span> <div class="actions mt-xs-3">  <button id="save-my-progress" type="button" class="btn btn-sm btn-primary text-center btn-xs-block"> <i class="fa fa-fw fa-floppy-o"></i> Save </button> </div> </div></div> <div id="modal-feedback" class="modal fade" tabindex="-1" role="dialog"> <div class="modal-dialog" role="document"> <div class="modal-content"> <div class="modal-header"> <h4 class="modal-title">Feedback</h4> <button type="button" class="close hidden-xs hidden-sm" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">&times;</span> </button> </div> <div class="modal-body"> <div class="errors"></div> <p><strong>Which of the following best describes your feedback?</strong></p> <form method="post" style="overflow: hidden"> <div class="form-group"> <div class="radio"><label style="color: #121212;"><input type="radio" name="feedback-type" value="Recommendation"> Recommend</label></div><div class="radio"><label style="color: #121212;"><input type="radio" name="feedback-type" value="Problem"> Report a problem</label></div><div class="radio"><label style="color: #121212;"><input type="radio" name="feedback-type" value="Improvement"> Suggest an improvement</label></div><div class="radio"><label style="color: #121212;"><input type="radio" name="feedback-type" value="Other"> Other</label></div> </div> <hr> <div class="row"> <div class="col-md-6"> <div class="form-group"> <label for="feedback-name">Name</label> <input type="text" class="form-control" name="feedback-name" placeholder="Name" value=" "> </div> </div> <div class="col-md-6"> <div class="form-group"> <label for="feedback-email">Email address</label> <input type="email" class="form-control" name="feedback-email" placeholder="Email" value="@airmail.cc"> </div> </div> </div> <div class="form-group"> <label for="feedback-comments">Comments</label> <textarea class="form-control" name="feedback-comments" style="resize: vertical;"></textarea> </div> <input type="hidden" name="feedback-ticket" value="082b9c9c4ae3624d"> <input type="hidden" name="feedback-url" value="https://studyib.net/physics/page/256/heat-transfer"> <input type="hidden" name="feedback-subject" value="6"> <input type="hidden" name="feedback-subject-name" value="Physics"> <div class="pull-left"> </div> </form> </div> <div class="modal-footer"> <button type="button" class="btn btn-primary btn-xs-block feedback-submit mb-xs-3 pull-right"> <i class="fa fa-send"></i> Send </button> <button type="button" class="btn btn-default btn-xs-block m-xs-0 pull-left" data-dismiss="modal"> Close </button> </div> </div> </div></div> </article> <hr class="hidden-md hidden-lg"> <div class="hidden-md hidden-lg mt-xs-3"> <button class="btn btn-default btn-block text-xs-center" data-toggle="modal" data-target="#modal-feedback" style="margin-bottom: 10px"><i class="fa fa-send"></i>&nbsp;&nbsp;Feedback</button> </div> </div> <input type="hidden" id="user-id" value="38342"></div><input id="ticket" type="hidden" value="082b9c9c4ae3624d"><input id="tzoffset" type="hidden" value="new"><input id="fp" class="fp" type="hidden" value=""></div><div id="std-footer"> <div class="wmap"> <div class="layout-wrapper"> <p> <a href="https://www.inthinking.net"> &copy; 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