How many 420nm photons are emitted per second by an LED with a power of 10 mW?

In summary, using the equation E=hc/lambda, we can calculate that for an LED emitting a light beam with a power of 10 mW and a wavelength of 420 nm, there are 2.1E16 photons emitted per second. This is found by dividing the power by the energy of one photon, which is calculated using Planck's constant and the wavelength of the light.
  • #1
XTEND
19
0

Homework Statement



An LED emits a light beam with a power of 10 mW. The wavelength of the light is 420 nm. How many 420nm photons are emitted per sec.?

Homework Equations



E=hc/lamda is 2.95E-9

P/E= Photons emitted per sec.

(10*10E-3)(2.95E-9)=2.952E-11


The Attempt at a Solution



2.95E-11 is wrong.

2.1E16 photons per/sec. is the answer
 
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  • #2
Your value for E is wrong.

h=6.626068 × 10-34 m2kg/s
 
Last edited:
  • #3
okay.

(6.626x10E-34)(3.0x10E8)=1.9878E-25 / 420nm = 4.7328E-28

(10x10E-3) / (4.7328E-28) = 2.1129E25

This is still not 2.1E16
 
  • #4
XTEND said:
okay.

(6.626x10E-34)(3.0x10E8)=1.9878E-25 / 420nm = 4.7328E-28

You forgot to convert nm to m.
 
  • #5
XTEND said:
okay.

(6.626x10E-34)(3.0x10E8)=1.9878E-25 / 420nm = 4.7328E-28

(10x10E-3) / (4.7328E-28) = 2.1129E25

This is still not 2.1E16


Check over your exponents in the part in red, it is not E-28.
 
  • #6
1.9878E-25/4.2E-7 = 4.7328E-19

(10x10E-3) / (4.7328E-19) = 2.1E16

Thank You!
 

Related to How many 420nm photons are emitted per second by an LED with a power of 10 mW?

1. What are photons emitted per second?

Photons emitted per second refers to the number of photons, or particles of light, that are emitted by a light source within a period of one second.

2. Why is it important to measure photons emitted per second?

Measuring photons emitted per second is important in many scientific fields, such as astronomy, optics, and particle physics. It allows us to quantify the intensity and energy of a light source, and can provide valuable information about the properties of the source.

3. How is the number of photons emitted per second calculated?

The number of photons emitted per second can be calculated by dividing the total energy of the light source by the energy of a single photon. This is known as the photon flux and is typically measured in units of photons per second (photon/s).

4. Can the number of photons emitted per second change?

Yes, the number of photons emitted per second can change depending on the properties of the light source. For example, a brighter light source will emit more photons per second than a dimmer light source.

5. How does the number of photons emitted per second relate to the wavelength of light?

The number of photons emitted per second is directly proportional to the energy of the light source, which is determined by its wavelength. In general, shorter wavelengths (such as ultraviolet or X-rays) have a higher energy and therefore emit more photons per second compared to longer wavelengths (such as radio waves).

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