What three factors affect the heat transfer that is necessary to change an object’s temperature?
The brakes in a car increase in temperature by
$\text{\Delta}T$ when bringing the car to rest from a speed
$v$ . How much greater would
$\text{\Delta}T$ be if the car initially had twice the speed? You may assume the car to stop sufficiently fast so that no heat transfers out of the brakes.
Problems&Exercises
On a hot day, the temperature of an 80,000-L swimming pool increases by
$1\text{.}\text{50\xbaC}$ . What is the net heat transfer during this heating? Ignore any complications, such as loss of water by evaporation.
Show that
$1\phantom{\rule{0.25em}{0ex}}\text{cal/g}\cdot \text{\xbaC}=1\phantom{\rule{0.25em}{0ex}}\text{kcal/kg}\cdot \text{\xbaC}$ .
To sterilize a 50.0-g glass baby bottle, we must raise its temperature from
$\text{22}\text{.}0\text{\xbaC}$ to
$\text{95}\text{.}\mathrm{0\xba}\text{C}$ . How much heat transfer is required?
The same heat transfer into identical masses of different substances produces different temperature changes. Calculate the final temperature when 1.00 kcal of heat transfers into 1.00 kg of the following, originally at
$\text{20}\text{.}\mathrm{0\xba}\text{C}$ : (a) water; (b) concrete; (c) steel; and (d) mercury.
Rubbing your hands together warms them by converting work into thermal energy. If a woman rubs her hands back and forth for a total of 20 rubs, at a distance of 7.50 cm per rub, and with an average frictional force of 40.0 N, what is the temperature increase? The mass of tissues warmed is only 0.100 kg, mostly in the palms and fingers.
$0\text{.}\text{171\xba}\text{C}$
A 0.250-kg block of a pure material is heated from
$\text{20}\text{.}\mathrm{0\xba}\text{C}$ to
$\text{65}\text{.}\mathrm{0\xba}\text{C}$ by the addition of 4.35 kJ of energy. Calculate its specific heat and identify the substance of which it is most likely composed.
Suppose identical amounts of heat transfer into different masses of copper and water, causing identical changes in temperature. What is the ratio of the mass of copper to water?
10.8
(a) The number of kilocalories in food is determined by calorimetry techniques in which the food is burned and the amount of heat transfer is measured. How many kilocalories per gram are there in a 5.00-g peanut if the energy from burning it is transferred to 0.500 kg of water held in a 0.100-kg aluminum cup, causing a
$\text{54}\text{.}\mathrm{9\xba}\text{C}$ temperature increase? (b) Compare your answer to labeling information found on a package of peanuts and comment on whether the values are consistent.
Following vigorous exercise, the body temperature of an 80.0-kg person is
$\text{40}\text{.}\mathrm{0\xba}\text{C}$ . At what rate in watts must the person transfer thermal energy to reduce the the body temperature to
$\text{37}\text{.}\mathrm{0\xba}\text{C}$ in 30.0 min, assuming the body continues to produce energy at the rate of 150 W?
$\left(\text{1 watt = 1 joule/second or 1 W = 1 J/s}\phantom{\rule{0.25em}{0ex}}\right)$ .
617 W
Even when shut down after a period of normal use, a large commercial nuclear reactor transfers thermal energy at the rate of 150 MW by the radioactive decay of fission products. This heat transfer causes a rapid increase in temperature if the cooling system fails
$(\text{1 watt = 1 joule/second or 1 W = 1 J/s and 1 MW = 1 megawatt})$ . (a) Calculate the rate of temperature increase in degrees Celsius per second
$(\text{\xbaC/s})$ if the mass of the reactor core is
$1\text{.}\text{60}\times {\text{10}}^{5}\phantom{\rule{0.25em}{0ex}}\text{kg}$ and it has an average specific heat of
$\text{0.3349 kJ/kg\xba}\cdot \text{C}$ . (b) How long would it take to obtain a temperature increase of
$\text{2000\xba}\text{C}$ , which could cause some metals holding the radioactive materials to melt? (The initial rate of temperature increase would be greater than that calculated here because the heat transfer is concentrated in a smaller mass. Later, however, the temperature increase would slow down because the
$5\times {\text{10}}^{5}\text{-kg}$ steel containment vessel would also begin to heat up.)
Questions & Answers
find the 15th term of the geometric sequince whose first is 18 and last term of 387
In this morden time nanotechnology used in many field .
1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc
2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc
3- Atomobile -MEMS, Coating on car etc.
and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change .
maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.