Physics, 27.01.2020 00:31 bella2331

What is total internal reflection? when does it occur?

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Total internal reflection is the phenomenon that occurs when a ray of light travels from a medium of high refractive index to a lower refractive index medium.

In this sense, the ray is refracted in such a way that it is not able to cross the surface between both media, being completely reflected.

This is the physical principle used in optical fiber to conduct light through the fiber without energy loss.

It is important to note, that this phenomenon occurs at a limit angle $\theta_{c}$ , which is calculated from Snell's law, substituting the angle of the second medium by $\theta_{2}=90\º$ :

$n_{1}sin\theta_{c}=n_{2}sin(90\º)$

Where $n_{1}$ and $n_{2}$ are the refractive indexes of both media.

Answer from: Quest

answer: the correct answer is 1.

explanation: there are various process in which a radioactive nuclei decays:

1) alpha decay: in this process, a heavier nuclei decays into lighter nuclei by releasing alpha particle. the mass number is reduced by 4 units.

$_a^z\textrm{x}\rightarrow _{a-2}^{z-4}+_2^4\alpha$

2) electron capture: in this decay process, a parent nuclei absorbs an electron and gets converted into a neutron. simply, a proton and an electron combines together to form a neutron. mass number does not change in this process.

$_a^z\textrm{x}+_{-1}^0\textrm{e}\rightarrow _{z-1}^a\textrm{y}$

3) gamma ray emission: it is a decay process in which an unstable nuclei gives excess energy by a spontaneous electromagnetic process. this decay releases $\gamma -radiations$ . this process does not change the mass number.

$_a^z\textrm{x}^*\rightarrow _a^z\textrm{x}+_0^0\gamma$

4) positron emission: it is a type of decay process, in which a proton gets converted to neutron and an electron neutrino. this is also known as $\beta ^+$ -decay. in this the mass number remains same.

$_a^z\textrm{x}\rightarrow _{z-1}^a\textrm{y}+_{+1}^0e$

from the above information, we see that only alpha-decay is producing a change in the mass number of the nucleus.

Answer from: Quest

colorectal cancer may also develop from areas of abnormal cells in the lining of the colon or rectum. this area of abnormal cells is called dysplasia and is more commonly seen in people with certain inflammatory diseases of the bowel such as crohn's disease or ulcerative colitis.

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