Task: Class Definition Understanding (ontology: Earth_Environment/OBOE)

Which of the following definitions best describes 'Knot'?

A. An einstein is a unit used in irradiance and in photochemistry. One einstein is defined as one mole of photons, regardless of their frequency. Therefore, the number of photons in an einstein is Avogadro's number, 6.022×1023.

Quantum flux of Photosynthetically active radiation (PAR) is usually reported in microeinsteins per second per square meter, one microeinstein being one-millionth of an einstein.

Irradiance might be measured in einsteins per square metre per second, if the source is monochromatic. (note: If the optical frequency is not well defined this is a sloppy misuse of the term irradiance, which is defined in terms of power per unit area, and p.


The einstein is used in studies of photosynthesis since the light requirement for the production of a given quantity of oxygen is a fixed number of photosynthetically active photons (about nine photosynthetically active einsteins per mole of oxygen formed).

It is named in honor of Albert Einstein, who in a 1905 paper explained the photoelectric effect in terms of light quanta, now called photons, an idea introduced by Max Planck.
B. The the concept (symbol: Pa) is the SI derived unit of pressure. It is a measure of force per unit area, and defined as one newton per sqare meter.
1 Pa = N m-2
C. The the concept is the unit of force derived in the SI system; it is equal to the amount of net force required to accelerate a mass of one kilogram at a rate of one meter per second per second. 
1 N = kg  m  s-2
D. A the concept is one nautical mile per hour, which is equal to exactly 1.852 km/h and approximately 1.151 mph.

Answer: A the concept is one nautical mile per hour, which is equal to exactly 1.852 km/h and approximately 1.151 mph.