F.3 phy questions

Help me solve following three phy questions plz ><

1) Jow has closed all windows of his car and parked his car under the Sun for three hours. When he opens a car door, he feels that the temperature inside the car is very high.

a. Explain briefly why temperature inside the car rises.

b. What would happed if parents leave their children unattended inside a car with all windows closed?

2) The central processing unit (CPU) of a computer is very hot and some effective cooling systems are thus invented.

a. State the mode of energy transfer that the cooling fan promotes.

b. Name two modes of energy tranfer that the copper fins lose heat.

c. Water has a high specific heat capacity than copper. However, we usually do not use water to replace the copper fins. Explain briefly.

d. Suggest a way to improve the cooling effect of the fan.

e. Some copper heat sinks are installed without fans. State one advantage and one disadvantage for such a cooling system.

3) Cathy is steaming fish in a wok. Initially there is 0.5kg of water at 25 degree in the wok. The wok is covered but steam can still escape through a hole in the cover. Explain why steaming is a good way to cook the fish.

Thx the one who help me =]

2 個解答

評分
  • 9 年前
    最愛解答

    1.

    a) The air inside the car gain infra-red radiation from the sun. The glass of the window reduces energy loss to the outside of the car. Therefore the temperature of the car rises.

    b) Their children may die because of the high temperature inside the car and the lack of air.

    2.

    a) Convection

    b) Radiation and conduction

    c) Water is a poor conductor of heat. Cooling effect is reduced.

    d) Increase the rotating speed of the fan.

    e) Advantage: Cooling can still occur when there is no power supply.

    Disadvantage: Cooling cannot be controlled and sometimes the temperature will be very high and cause damages to the CPU.

    3. Latent heat of vaporization of water is high (2.26 x 10^6). Time to cook the fish can be reduced.

    資料來源: own knowledge
  • 天同
    Lv 7
    9 年前

    I give you the points and you should elaborate them by yourself.

    1(a) It is because of near infrared radiation from the sun that penetrates the glass windows of the car. The far infrared radiation re-emitted is retained by the glass windows, thus raising the temperature inside the car.

    (b) Parents should not do this as it would endanger the life of their kids due to high temperature.

    2. (a) Forced convection.

    (b) Convection and radiation.

    (c) Copper is a good conductor of heat, but water is not.

    (d) Use a fan of larger dimension (diameter) and/or increase the blowing speed of the fan.

    (e) Advantage: cooling can still be effective when the computer is turned off.

    Disadvantage: cooling effect cannot be adjusted when there is a sudden rise of teperature in the computer.

    3. It makes use of the high latent heat of vapourization of water to cook the fish.

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