Urgent question 2

2009-03-18 3:03 am

Explain and shows the steps clearly.

1. Which of the following statements about greenhouse effect of the Earth is/are correct?
(1) Thinning of the ozone layer in the atmosphere enhances the greenhouse effect, resulting in global warming.
(2) Water vapour, CO2 and certain gases in the atmosphere absorb infra-red radiation emitted by the Earth surface.
(3) At quilibrium, the incoming and outgoing radiation are balanced, the Earth's average temperature remains relatively constant.

2. Air to glass. (Bend towards the normal/ bend away from the normal)

3. There are three parallel straight wires P, Q and R. P carries currents flowing into the paper. Q and R carry a current flowing out of the paper. Suppose the wires are equidisant from each other and magnitudes of currents in them are the same. What is the direction of the resultan force acting on R?

更新1:

4. Which of the following about the formation of a rainbow is correct? (1) Sunlight composes of light of different colors. (2) The raindrops in th sky refract the sunlight into different colors. (3) Lights of different colors interfere with each other to form a rainbow.

更新2:

Please explain Q.4 also.

更新3:

That means Q.3 The resultant force acting on R is pointing downwards? Please help me to solve the questions in "Urgent question 3".

回答 (1)

Prof. Physics

2009-03-18 4:29 pm

✔ 最佳答案

1. The correct statements are (2) and (3).

Statement (1), The thinning of ozone layer enhances the incidence of ultra-violet light from the Sun, thus increasing the exposure of UV-radiation in the Earth. It has nothing to deal with greenhouse gases.

Statement (2), such gases are efficient in absorbing the infra-red radiation, thus they can trap heat from the radiation and keep the Earth warm.

Statement (3), This is the fact.

2. The refractive index of air (1.00003) is smaller than that of the glass (about 1.5).

When light passes from a optical less densed medium to a optical denser medium, the velocity of the light decreases and hence the light bends towards the normal. (A result from Snell's law, or more general, Huygen's principle.)

From Snell's law, n1sin@1 = n2sin@2,

with n1 < n2, @1 > @2, hence it bends towards the normal.

3.

圖片參考：http://i726.photobucket.com/albums/ww265/physicsworld2010/physicsworld01Mar180828.jpg?t=1237336163

F1 - Force on R due to Q

F2 - Force on R due to P

F - Resultant force on R

4. The correct statements are (1) and (2).

Statement (1), sunlight is mainly white light, in which it contains a continuous range of wavelength of light. That is, it is a composite of light of different colors.

Statement (2), Different colours of light have different refractive index when they are refracted in raindrops. Resulting in different refracting angles and hence the colours can be separated.

Statement (3), this is not true.

參考: Physics king

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