Answer:
D. infinitely extended in all directions
Explanation:
A semi infinite solid is infinitely extended in every direction. It has a single surface and can extend when heat is applied.
The body of a semi infinite solid is idealised, that is, when there is heat present, it expands in all directions to infinity. It can be used for a thick wall because its shape can be changed when subjected to different levels of heat near its surface.
It is also expands as heat is applied because its thickness is negligible.
This idealized body is used for earth, thick wall, steel piece of any shaped quenched rapidly etc indetermining variation of temperature near its surface & other surface being too far to have any impact on the region in short period of time since heat doesn’t have sufficient time to penetrate deep into body thus thickness can be neglected
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Answer : The energy of one photon of hydrogen atom is, 
Explanation :
First we have to calculate the wavelength of hydrogen atom.
Using Rydberg's Equation:

Where,
= Wavelength of radiation
= Rydberg's Constant = 10973731.6 m⁻¹
= Higher energy level = 3
= Lower energy level = 2
Putting the values, in above equation, we get:


Now we have to calculate the energy.

where,
h = Planck's constant = 
c = speed of light = 
= wavelength = 
Putting the values, in this formula, we get:


Therefore, the energy of one photon of hydrogen atom is, 
I believe that solar energy would be the best energy for my town. Solar energy is advantageous because the sun is up every day, and because it takes up much less space than than some other sources of renewable energy. Some disadvantages of solar energy are that if there is cloud cover, hardly any energy will be gained at all. Another disadvantage is that it is a long term investment that can take a while for it to pay for itself.
Answer:
The correct answer is option D i.e. A and C
Explanation:
The correct answer is option D i.e. A and C
for proficient catching player must
- learn to absorbed the ball force
- moves the hang according to ball direction to hold the ball
- to catch ball at high height move the finger at higher position
- to catch ball at low height move the finger at lower position