Question

How many photons per second are emitted by the antenna of a microwave oven if its power output is 1.00 kw at a frequency of 2515 mhz?

Answer 1

The power of the antenna is
$P=1.00 kW=1000 W$
and since the power is the emitted energy divided by the time, the energy emitted per second is
$E=Pt = (1000 W)(1 s)=1000 J$

The frequency of the emitted photons is
$f=2515 MHz=2.515 \cdot 10^9 Hz$
So the energy of a single photon is
$E_1=hf=(6.6 \cdot 10^{-34} Js)(2.515 \cdot 10^9 Hz)=1.66 \cdot 10^{-24} J$

Therefore, to find the number of emitted photons per second, we should divide the total energy emitted by the antenna in 1 second by the energy of a single photon:
$N= \frac{E}{E_1}= \frac{1000 J}{1.66 \cdot 10^{-24} J}= 6.02 \cdot 10^{26}$