IGCSE Physics - SI Units and Prefixes
8.3 هزار بار بازدید -
7 سال پیش
-
All seven SI units: metre/meter,
All seven SI units: metre/meter, second, kilogram, mole, candela, kelvin, ampere/amp all explained in this video. As well as the majority of the standard prefixes you will ever encounter including the hecto, micro, nano, and tera.
In this video I will be covering SI Units and Prefixes.
Si Units
Having a Basic understanding of SI units is extremely important for all the sciences. They are the standardized method of measurement and there are 7 base SI units from which other measurements are derived.
They are the metre, which is defined as "the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second."
The Kilogram defined as "anything equal to the mass of the International Prototype of the Kilogram".
The Second which is defined as "the time that elapses during 9,192,631,770 cycles of the radiation produced by the transition between two levels of the cesium 133 atom"
And by now you are definitely wondering why in god's name are these definitions so weird? And the answer is the units were derived before the definitions and so scientists tried to find a constant in nature that equals the unit we created.
Moving on...
The Kelvin is the SI unit for temperature and can be converted to celsius by -273.15 from the reading. This is because the Kelvin starts at a temperature lovingly named absolute zero which is the lowest temperature theoretically possible where the particles of a solid stop vibrating.
The SI unit for electrical current is the ampere or the amp defined as "that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in vacuum, would produce between these conductors a force equal to2×10−7 newtons per metre of length."
And no I don't know what that means.
Next is the SI unit for luminous intensity and that is the Candela which is defined as "the luminous intensity in a given direction of a source that emits monochromatic radiation of frequency 540 × 10 12 hertz and has a radiant intensity in that same direction of 1/683 watt per steradian (unit solid angle)."
Finally the SI unit for amount of stuff is the Mole. The mole can be defined by whatever is written here but more simply a mole is just the number 6.02 times 10 to the 23rd power literally. For example a mole of ice cream would be 6.02 times 10 to the 23rd power ice creams.
Next on the agenda is to cover SI Unit Prefixes, the bits that go on the beginning. Starting with femto which makes a unit 10 to the -15 smaller, then the pico which is 10 -12, nano which is a billion times smaller than the base unit, micro which is a million times smaller, mili is a thousand times smaller, centi a 100, and deci 10.
Then things start getting bigger
Deca makes things ten times bigger, hecto 100x, kilo 1000x, Mega makes things 1000000 times bigger but it doesn't stop there. We still have Giga, Tera, and Peta.
So those are all the prefixes you'll ever need in school but there are prefixes for smaller and bigger things.
Finally, those who were attentive may remember me mentioning that SI units are used to derive measurements such as speed which is distance divided by time. Or density which is derived from kilograms per cubic meter.
In this video I will be covering SI Units and Prefixes.
Si Units
Having a Basic understanding of SI units is extremely important for all the sciences. They are the standardized method of measurement and there are 7 base SI units from which other measurements are derived.
They are the metre, which is defined as "the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second."
The Kilogram defined as "anything equal to the mass of the International Prototype of the Kilogram".
The Second which is defined as "the time that elapses during 9,192,631,770 cycles of the radiation produced by the transition between two levels of the cesium 133 atom"
And by now you are definitely wondering why in god's name are these definitions so weird? And the answer is the units were derived before the definitions and so scientists tried to find a constant in nature that equals the unit we created.
Moving on...
The Kelvin is the SI unit for temperature and can be converted to celsius by -273.15 from the reading. This is because the Kelvin starts at a temperature lovingly named absolute zero which is the lowest temperature theoretically possible where the particles of a solid stop vibrating.
The SI unit for electrical current is the ampere or the amp defined as "that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in vacuum, would produce between these conductors a force equal to2×10−7 newtons per metre of length."
And no I don't know what that means.
Next is the SI unit for luminous intensity and that is the Candela which is defined as "the luminous intensity in a given direction of a source that emits monochromatic radiation of frequency 540 × 10 12 hertz and has a radiant intensity in that same direction of 1/683 watt per steradian (unit solid angle)."
Finally the SI unit for amount of stuff is the Mole. The mole can be defined by whatever is written here but more simply a mole is just the number 6.02 times 10 to the 23rd power literally. For example a mole of ice cream would be 6.02 times 10 to the 23rd power ice creams.
Next on the agenda is to cover SI Unit Prefixes, the bits that go on the beginning. Starting with femto which makes a unit 10 to the -15 smaller, then the pico which is 10 -12, nano which is a billion times smaller than the base unit, micro which is a million times smaller, mili is a thousand times smaller, centi a 100, and deci 10.
Then things start getting bigger
Deca makes things ten times bigger, hecto 100x, kilo 1000x, Mega makes things 1000000 times bigger but it doesn't stop there. We still have Giga, Tera, and Peta.
So those are all the prefixes you'll ever need in school but there are prefixes for smaller and bigger things.
Finally, those who were attentive may remember me mentioning that SI units are used to derive measurements such as speed which is distance divided by time. Or density which is derived from kilograms per cubic meter.
7 سال پیش
در تاریخ 1396/07/08 منتشر شده
است.
8,369
بـار بازدید شده