consider a brick wall that has been exposed to the sun for some time.

1.how did the heat get from the sun's surface to the wall?(is it something about radiation?please help.)

2.the air over the wall seems to shimmer and shake as air currents rise from it.explain what creats these air currents.

3.which would you expect to be warmer after being exposed to the sun for equal times-a white wall or a black wall?explain. (is it the black wall because black absorbs heat while white reflect light and heat?or is there another reason?)

thx

1) Radiation from the sun, mostly the visible light the sun emits, travels through space. Some of it arrives at Earth.

2) Gravity. Very very close to the wall the air has the same temperature as the wall, but very slightly away from the wall the temperature is much lower than the wall. This is because air conducts heat very inefficiently. So, near the wall you have large temperature gradients.

If the temperature gradient is sufficiently high, a small bubble of hot air can rise up from the wall and remain warmer than the surrounding air despite it cooling down a bit because of adiabatic expansion. Because a hot bubble of air has a lower density than the cold air it is in after rising up, it will continue to float upward. This process drives the air currents and is called "convection".

3. This is usually wrongly explained in high school. You can have white bricks that will become hotter than bricks that are black. When the brick reaches a certain steady state temperature, the total energy it is absorbing per unit time equals the energy it losing (due to radiation, convection etc.) to the environment.

A white wall will absorb less heat from the sun, as most of it will be reflected away. However, the amount of heat an object emits per unit time in the form of radiation is determined by how well it absorbs infrared radiation (i.e. by "how black" it is). A wall that is black in the infrared will emit more radiation per unit time at the same temperature than a wall that is white in the infrared.

Now most bricks will absorb infrared radiation pretty well, so assuming that you have a white wall and a black wall, both of which are black in the infrared, then the black wall will become hotter.

THANK YOU SO MUCH!!!

You're welcome! I'm glad I could help explain these concepts to you. Let me know if you have any more questions!