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convection requires a medium is not the main difference, it is simply the most obvious aspect of what is a fundamentally different mechanism for transfering energy. Convection is the transfer of energy by movement of a medium, whereas radiation is the transfer of energy by, well, thermal radiation. Conduction also requires a medium, but, again, it is a fundamentally different mechanism than either convection or radiation; in this case it is the transfer of energy through a medium.
Unfortunately, analogies are hard but if you can visualize the particles involved, it would help. Picture the red hot iron you mentioned. On a molecular level, the material is emitting lots and lots of photons (hence why it is glowing red). The creation of these photons takes energy; energy from the heat of the iron. These photons leave the iron, pass through the environment, and eventually collide with some other object where they are absorbed and deposit their energy. This is radiative heat transfer. If that energy is deposited on your retina or a CCD (like in a digital camera), an image forms over time. This is how infrared goggles work and they would work equally well in high vacuum as here on earth.
In conduction, the next simplest example, there is no generation of photons (physics nerds forgive me for the sake of simplicity). The individual atoms in the object are vibrating with heat energy. As each atom gains energy from it's more energetic neighbors, so it gives up energy to its less energetic ones. Over time, the heat "travels" through the object.
In convection, the molecules of gas near the object gain energy, like in the conduction case, but those same molecules that gained energy then travel through the environment to some other location where they then give off their heat energy.
In summary:
radiation = generated and absorbed photonsconduction = molecules exciting their neighbors succesivelyconvection = molecules heated like in conduction, but then move to another location
As young as 10 years old
have a good day :)
Answer:
Having.
Explanation:
When we are working with Select statements like COUNT(CustomerID).We should use Having clause because functions like (SUM,COUNT,AVG etc) are aggregate functions and we cannot use where clause with aggregate functions.That's why we use Having clause with aggregate functions.
for example:-
select COUNT(CustomerID),state_of_residence
from Customers
GROUP BY state_of_residence
HAVING COUNT(CustomerID)>10;
<h2>
Answer:</h2>
(a) mkdir /d D:\utilities\recover
or
mkdir D:\utilities\recover
(b) rd /s D:\software\arch98
<h2>
Explanation:</h2>
(a) To make a new directory we use the md or mkdir command followed by the name of the directory as follows;
mkdir [name_of_directory]
The name of the directory could also be a relative or absolute path depending on the request.
In the task, the specified directory uses an absolute path given as D:\utilities\recover. This path is in a drive D. Therefore, if you are in another drive different than D, to run this command, it is a great idea to do that with the /d switch.
In summary:
i. if in drive D, to make a directory D:\utilities\recover, type the following command;
mkdir D:\utilities\recover
ii. if otherwise in a different drive, type the following command.
mkdir /d D:\utilities\recover
(b) To delete a directory, we use the rd or rmdir command. If the directory has contents that also need to be deleted, we use the switch /s alongside the rd or rmdir.
In the task given, the directory to be deleted is D:\software\arch98. This includes deleting all of its files too. To do this, type the following command;
rd /s D:\software\arch98
