PHY12 Thermal Physics Problems with solution.pdf

PHY12 – Thermal PhysicsEngr. Ricardo F. De Leon, Jr. 1. 1990 April ECE Board If the freezing point of water is 0C or 32F, and its boiling point is 100C or 212F, which relationship is correct? A. C. B. D. SOLUTION: If we let equals a temperature reading in the Fahrenheit scale and the Celsius scale and then applying the ratio and proportion technique, to be a temperature reading in Therefore, 2. 2000 April ECE Board One cubic meter of water inside a 1 kg aluminum container is heated from 20C to 30C. Find the heat supplied to the system if =0.22 cal/g-C. Note: Assume that there is no heat loss and the temperature of water is always equal to the temperature of aluminum container. A. 20 002 200 cal C. 10 002 200 cal B. 30 002 200 cal D. 40 002 200 cal SOLUTION: The total heat supplied to the system is For water, the heat supplied is = = For aluminum container, the heat supplied is = = Therefore, the total heat supplied is 1|Page L Lf o x L X=? 5m o SOLUTION: L f  Lo (1   T )     L f  5m 1  30  10 6 / C 30 C L f  5. 19. De Leon.39 grams C.12 grams D. If the coefficient of linear expansion of the bar is 30 x 10 -6/C. 1996 October EE Board How much oil at 200C must be added to 50 grams of the same oil at 20C to heat it to 70C? A. 12. Ricardo F.PHY12 – Thermal Physics Engr.23 grams B. 23. 3.2122 m 2|Page . 4. A 10-m length bar with a crack at its center buckles up due to an increase of temperature of 30C.0045 m2  5m2 x  0. find the vertical displacement of the center. 29.91 grams SOLUTION: Law of Heat Exchange. Jr.0045 m Using Phytagorean Theorem: x 5. involved for the hot tea is purely sensible heat. mct ice Additional heat is required to melt the ice. Find the temperature at the interface? How much heat is conducted in one hour? STEEL SILVER interface SOLUTION: a. temperature at the interface H silver  H steel  k silver Asilver Tsilver k steel Asteel Tsteel  Lsilver Lsteel    406 W m  K 6 x10  4 m 2 t i  0C  50. The free end of the silver rod is submerged in an ice bath and the free end of the steel rod is placed in a steam bath.PHY12 – Thermal Physics Engr. Ricardo F. Jr. Qlo ss  Q g a in ed  0 (mct ) tea  (mct ) ice  mice L f  mice c wa ter t wa ter  0 (1500 g )(1cal / g  C )(1C  100 C )  mice [(0.5 liters of red tea (mostly water) from a temperature of 100C to 1C by adding up ice at -15C. At thermal equilibrium.   Since the heat The temperature of the ice is subzero.97 grams 6. mice cwater t water .5cal / g  C )(15C )  80cal / g  (1cal / g  C )(1C  0C )]  0 mice  1677. 5.5 m t i  19.2 W m  K 6 x10  4 m 2 100 C  t i   1m 0. Qloss  mct tea . De Leon. Two rods (50-cm steel and 100-cm silver) with 6 cm2 cross sectional area are connected to one another.83 C answer 3|Page . How much ice should he add to carry out the task? Neglect any heat transfer to the environment. Poppy wants to cool 1. Heat is needed to increase the temperature of the ice from -15C to 0C. SOLUTION: The hot tea will give off the heat while the ice will absorb all the heat. m ice L f and more heat   is needed to increase further its temperature to 1C. 67x10  8 2 4  3084  2884  m K   answer Pnet   180 .38 W atts answer H   273 354  b. net rate of heat loss. Q  A e T 4 t  W H  1. b.67x10  8 2 4 m K  H  765. De Leon.PHY12 – Thermal Physics Engr. what is the rate of radiation of energy from the body? If the surroundings are at a temperature of 15C.12 Joules answer 7. what is the net rate of heat loss from the body by radiation? Assume that the human body is a black body. total rate of radiation of energy from the human body.83C  0C  Q x3600sec 1m Q  17390.5 m 2 1   5. heat conducted in one hour Tsilver Q  k silver A silver t Lsilver   406W m  K 6 x10 4 m 2 19. Jr.26 Watts 4|Page . SOLUTION: a. Ricardo F. Assuming that the total surface area of a human body exposed is 1.5 m2 and the surface temperature is 35C. Pnet  A e T14  T24   W  Pnet  1.5 m 2 1   5.