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## Class 11 Physics (India)

### Course: Class 11 Physics (India)>Unit 2

Lesson 1: Physical quantities and their measurement

# Scale of the small

From honey bees to cells, viruses, and atoms -- understanding the scale of the very small. Created by Sal Khan.

## Want to join the conversation?

• Is there anything smaller than a femtometer?
• yes, the Planck length. But remember, its not like we can measure or perceive the planck length in any way at all. it is FAR beyond the capability of anything we know or can even conceive of to measure. Also, scientists believe that there may not BE anything smaller than the planck length. It may be that it's the smallest individual unit the universe can produce. think of it as the maximum resolution of our universe. In other words, you could travel from one planck length to the next without moving through anything. The same is true for planck time. There may be no time between units. these planck measurements may be the universes maximum resolution in time and space!
• Smaller creatures like honey-bee would be able to see things we cannot see like dustmites right?
• Yes, their eyes are tuned to see smaller things than a human eye can, assuming they have eyes of course.
• I've got a question. Even though microscopes allow us to see very far into an item, is it possible to make something to see the atoms that make up our air?
• Yes, that would be possible. Currently the strongest microscope can look at atoms, for example gold atoms. you can find more information here:
And then there is this years Nobelprize in Chemistry for a new typ of light microscope that can look at things in even greater detail than earlier light microscope! (not yet better than the best electron microscopes)
• If an AIDS virus is that small, how is it able to destroy a white blood cell so easily?
• Viruses hijack the cell's machinery and get it to make more viruses. When there is a whole lot of viruses in the cell, the cell just explodes. Then all those viruses go off to hijack and explode more cells.
• what makes the electron to move around the nucleus and why there is a free space in between?
• Electromagnetism. The nucleus is positively charged, and the electron is negatively charged. The electron has speed which keeps it in its "orbit".
• I was wondering if there are any metric prefixes that are less than a yoctometer? I see the Planck length, but that is not what I mean, I mean actual prefixes (zepto, pico, etc.)
• There are no offical metric prefixes less than a yoctometer, but here is a list of all the metric units less than a meter:

meter (m): 1m
decimeter (d): 0.1m
centimeter (c): 0.01m
millimeter (mm): 0.001m
micrometer (μ) : 0.000001m
nanometer (n): 0.000000001m
picometer (p): 0.000000000001m
femtometer (f): 0.000000000000001m
attometer (a): 0.000000000000000001m
zeptometer (z): 0.000000000000000000001m
yoctometer (y): 0.000000000000000000000001m

If you have any more questions or need more detail, comment below...
• Is there anything beyond the Planck Length? And is the Planck Length a theory, or have we actually detected it in any way?
• Plank length is not a theory than the meter is a theory. How do you detect a length? From experimentation there are some natural constants like the strength of gravity, speed of light, pi that are measured or defined that were used to create natural units. One of these is the plank length.

If you are asking if anything exists smaller than the plank length we don't know because we cont measure anywhere close to that precisely.
• this is a bit of a complicated question, but the timestamp of where I have a question is: and the Quantum realm. i went to KA Quantum Physics library, and i understand that the basis of calling it a "realm" is were physics get wonky, but he says that "its hard to define where one thing ends and one thing begins; what is real? what is not real?" why does he say that? is it just because we have no way to accurately observe things that small? also, what is the size comparison between a Planck measurement and an Angstrom? sorry this question was a bit lengthy
• Quantum physics is a matter of probability rather than certainty. We can see the physical effects of atoms, so it is useful to consider them an object, but an atom is made of parts that are also moving. In practice, we can only define where the electrons probably are at any given time, and while the reasons why are hard to simplify, it's not practical to describe "where" they must be. It's very likely that two electrons are within a small spherical area around the nucleus, assuming we're dealing with an element that has 2 or more electrons, but not certain. Defining where one thing ends means choosing what probability we care about - for example, is the radius of an atom where the electrons are 50% of the time? 75%? 99%? Due to the weirdness of quantum physics - often referred to as the quantum effect - the only way to say with 100% certainty that something is within a range of locations is to include all locations that exist in the universe. Saying where another thing begins is hard for similar reasons - and I'm excluding interactions of atoms for the sake of simplicity.

The Planck length is defined as 1.616m * 10^-35. As an angstrom is 1m * 10^-10, one way to compare those is to estimate the Planck length as 1m *10^-35, and say that it is about 1/(10^25) of an angstrom. This is absolutely bonkers small - a rough size comparison between an angstrom and a Planck length is that of the diameter of the Milky way (roughly on the order of 10^20) to that of an angstrom (at 10^-10). The idea of a length smaller than the Planck length is essentially useless, as even the strings of string theory would be in units of Planck lengths.