If anyone is here
I'm not sure, sorry, hopefully somebody catches this before the exam
I tried rotating it both ways in my head and both times got current from X to Y initially, not sure if it's a bad question or if I just stuffed up the logic somewhere.
PLeaseee:
A beam of red light of frequency 4 × 10^14 Hz is found to deliver 7.54 × 10^19 photons per second.
What would be the power of the beam?
P=E/t
E = number of photons x single photon energy
= 7.54 x 10^19 x hf
= 7.54 x 10^19 x 6.63 x 10^-34 x 4 x 10^14
so P=(that)/1=that
EDIT: I used the Js version of h because we want energy in Joules so that we can have Power in Watts (Joules/second), if we had have used the eVs value of h (the 4.14x10^-15 one) we would have got energy in eV meaning power in eV/s which isn't a standard unit for power, afaik.
Hopefully that makes sense, the key idea is that the energy of a beam is the number of photons times the energy of one photon
Good luck today everyone!