Problem with units when using E=hv

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In summary, the formula for energy of a photon is E=hf or E=hc/λ, where f is frequency, c is the speed of light, and λ is the wavelength. The second formula is used when frequency is unknown and combines the equations for frequency and energy. When using E=hc/λ, the units for energy are kg*m2/s3. To convert the units to Joules, the value for Planck's constant, represented as J*s, should be used instead of just s. It is important to carefully check the signs of exponents when working with these equations.
  • #1
Aspchizo
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In case I'm wrong, the formula for energy of a photon is E=hf.
Or E=hc/λ, because f=c/λ.

Basically the second formula is just in case you don't know frequency so it crams the equation for that into the equation for energy.

When I use E=hc/λ the units I get are...

kg*m2/s3

What I did was... A photon of red light, has a wavelength of like 700nM, so...

(6.626×10-34kg*m2/s2) (3x108m/s) / 7×107m

= 2.84×1019kg*m2/s3

I thought the answer would be in Joules, which is kg*m2/s2, so I must be missing something... Why the extra unit of time.
 
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  • #2
Wow stupid, Planck's constant is J×s which is kg*m2/s

Well, everything else looks okay?
 
  • #3
Check the signs of your exponents. Everything else looks right, if you fix your units.
 
  • #4
Ah right, ^-19

Thanks
 

1. What is the equation E=hv and what does it represent?

The equation E=hv is known as the Planck-Einstein relation and it represents the relationship between energy (E) and frequency (v) of electromagnetic radiation. It states that the energy of a photon is directly proportional to its frequency.

2. Why is it important to use proper units when using E=hv?

Using proper units is important in any scientific calculation, but it is especially crucial when using E=hv. This is because the units for energy and frequency are different, and using the wrong units can lead to incorrect results. Additionally, E=hv is often used in complex equations and any unit errors can have a cascading effect on the final result.

3. What are the units for energy and frequency in E=hv?

The units for energy in E=hv are joules (J) and the units for frequency are hertz (Hz). However, in some cases, other units such as electron volts (eV) or angular frequency (rad/s) may be used for energy and frequency respectively.

4. Can E=hv be used for all types of electromagnetic radiation?

Yes, E=hv can be used for all types of electromagnetic radiation, including visible light, radio waves, X-rays, and gamma rays. This is because all forms of electromagnetic radiation exhibit wave-like properties and therefore have a frequency and energy associated with them.

5. How does E=hv relate to the photoelectric effect?

The photoelectric effect refers to the phenomenon where electrons are ejected from a metal surface when exposed to light of a certain frequency. This phenomenon can be explained by E=hv, as it shows that the energy of a photon is directly proportional to its frequency. Therefore, only photons with a certain energy (or frequency) can have enough energy to eject electrons from the metal surface, causing the photoelectric effect.

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