Formulae for energy of photon (E=hf and E=hv) I have seen the energy of a photon given by the formulas:

$$E = h \cdot f \tag{1}$$ 
Where $E$ = energy of the photon, $h$ = Planck's constant, $f$ = frequency of radiation (Source: BBC article)

I've also seen it given as

$$E= h \cdot \nu \tag{2}$$ 
Where $\nu$ stands for frequency (Source: Wikipedia article)

But in this topic I've also seen

$$f=\nu/\lambda \tag{3}$$ 
Where $\nu$ = speed, $\lambda$ = wavelength (Source: Simple English Wikipedia article)

Is there any difference between equation 1 and equation 2? And is equation 3 unrelated?
I understand your confusion. They all are actually the same formulas. It is because lets start with the first equation,

$$E=h \cdot f$$

But we know that frequency can be written in terms of speed formula,
$$ v = f \cdot \lambda$$

Which can be rearranged into the following,
$$ \frac{v}{\lambda} = f $$

If you put that expression into the above equation, then that becomes

$$ E = f \cdot \frac{v}{\lambda}$$

Hence the same formula can be written in many ways. 



Your first two equations are just the same. $f$ usually stands for frequency and in the second equation you have just used $\nu$ for it. That is the frequency of the photon that is coming in or being released.

Whereas your third equation actually comes from the speed formula as I have written above,
$$ v = f \cdot \lambda$$

Rearranging for frequency, you get:
$$ \frac{v}{\lambda} = f $$