-- The energy of one photon is <em>(h · frequency of the light)</em>
' h ' is 6.626 × 10⁻³⁴ m²-kg/s ("Planck's Constant")
-- The question doesn't tell you the frequency of the light from the LED, but it tells you the wavelength, and
<em>Frequency = (speed of light) / (wavelength) </em>.
-- Now you have everything you need to calculate the <em>energy carried by one photon from the LED</em>.
-- The power of the light from the LED is 120 milliwatts. That's <em>0.120 Joule of energy per second</em>.
Now you should be able to find the number of photons per second. It's going to be <em>(0.120 Joule) / (energy carried by one photon)</em> .
When I scribbled it out on a scrap of scratch paper, I got 3.853 x 10³⁸ photons, but you'd better really check that out.
Windmills run on the principle of mechanical energy and work. Moving air (wind) possesses some amount of energy in the form of kinetic energy (due to motion). This energy gives the air the ability to do work on the blades of the fan.
Answer:
v = R w
With this expression we see that for each point at different radius the tangential velocity is different
Explanation:
They indicate that the angular velocity is constant, that is
w = dθ / dt
Where θ is the radius swept angle and t the time taken.
The tangential velocity is linear or
v = dx / dt
Where x is the distance traveled in time (t)
In the definition of radians
θ = s / R
Where s is the arc traveled and R the radius vector from the pivot point, if the angle is small the arc (s) and the length (x) are almost equal
θ = x / R
We substitute in the speed equation
v = d (θ R) / dt
The radius is a constant for each point
v = R dθ / dt
v = R w
With this expression we see that for each point at different radius the tangential velocity is different
Since we are ignoring air resistance which is a non-conservative force, the potential energy will be completely converted into kinetic energy, resulting in a final kinetic energy of
.
