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        riddles >> easy >> [real life / physics] Making tea
        
(Message started by: BNC on Jan 19^th, 2004, 8:52am)

Title: [real life / physics] Making tea
Post by BNC on Jan 19^th, 2004, 8:52am

Williwutang and April Underwood finally got together, and decided to go camping. Willy was in charge of the arrangements, and as a low-cash student, settled for a low-cost motel.
And what a mistake that turned out to be! The place was dirty, the other guests un-friendly, not to mention the TV set was not working!

Comes morning, Willy and April want to leave the pace as fast as possible. April, however, being English, will not leave before drinking her morning tea, together with her boyfriend Willy. Unfortunately, the water heater is broken as well. luckily, April packed a couple of Heating coils (http://[http://www.magellans.com/jump.jsp?itemType=PRODUCT&iProductID=636).

As time goes by, April becomes more and more irritated. It is up to Willy to make the tea, and make it QUICK!

1. The cups available are wide. Willy may use the two heating coils to heat the two cups simultaneously (one coil per cup) or use both coils on one cup, and then on the other. Which way is faster?

2. Now the water boiled. Willy would like to add a teaspoonful of sugar to his cup. He also likes to drink his tea at room temperature. Which is faster -- dissolving the sugar when the water is hot, and then wait for it to cool, or wait for it to cool, and then add the sugar?

3. April managed to get an ice cube. Which way is faster -- placing the ice into the boiling hot water, and then wait for the rest of the cooling-down, or the other way around?

Title: Re: [real life / physics] Making tea
Post by towr on Jan 19^th, 2004, 9:15am

1 and 3 are similar in some respects,
::[hide]the rate at which the temperature changes depends on the temperature difference, and the area over which heat transport occurs.
For 1 this means that as the cups get's hotter it looses more heat to the room. Since it will take longer to heat the cup with one heater (as it his a smaller area than two), more energy will be lost in that extra time (which means you need even more time to compensate). So it will be faster to put both heaters in a cup at a time.

In 3 more heat will leave the cup at the beginning, so it will cool faster that way. Of course one could also mention that the temperature goes asymtoticly to room temperature, so if you add the ice first you will never reach it ;)
(Of course if you ask the ice at the end there is the risk you overshoot your target temperature)[/hide]::

Title: Re: [real life / physics] Making tea
Post by Sameer on Jan 19^th, 2004, 9:22am

I think on the 3 you just created another temperature difference system: hot one being tea and cold one being ice.. and that heat exchange will take place between those resulting in melting of ice and again reaching the room temperature faster (because your original system was boiling cup and room which had lower temp difference)

Title: Re: [real life / physics] Making tea
Post by rmsgrey on Jan 20^th, 2004, 8:55am

#2 ::[hide]probably depends on how much more readily sugar dissolves in hot tea than in cold and on how much heat is released/absorbed by sugar when it dissolves. If it releases heat, then the sooner it's added the better; absorbing heat is best left till later. Adding the sugar too late means you then have to wait for it to dissolve.[/hide]::

[e]closing hide tags[/e]

Title: Re: [real life / physics] Making tea
Post by Sameer on Jan 20^th, 2004, 9:10am

I would say #2 is more of physical chemistry than physics. I mean need to understand the solvent and solution at given temperatures.