IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: winnie101 on November 30, 2010, 12:48:30 pm

Title: photoelectric emission
Post by: winnie101 on November 30, 2010, 12:48:30 pm: could someone plz help me with the following
A particular filament rating of 60W emits 5% of this power as visible light. The average wavelength of visible light is 550nm.
Calculate the number of photons of visible light emitted per second from the lamp.
Thanks
Title: Re: photoelectric emission
Post by: Deadly_king on December 02, 2010, 10:52:13 am: Quote from: winnie101 on November 30, 2010, 12:48:30 pm
could someone plz help me with the following
A particular filament rating of 60W emits 5% of this power as visible light. The average wavelength of visible light is 550nm.
Calculate the number of photons of visible light emitted per second from the lamp.
Thanks

The 5% power is defined as the energy required for $x$ number of photons to be emitted per second.

Hence Power = $x$ x $E$ where $E$ = photon energy = $hc$ /lambda

Power = $x$ x $hc$ /lambda -----> 5/100 x 60 = $x$ x (6.63 x 10^-34) x (3 x 10⁸) / (550 x 10^-9)

Thus $x$ is found to be 8.3 x 10¹⁸ which is the required answer.

Sorry for late reply...........but I was kinda busy. :-[
Title: Re: photoelectric emission
Post by: winnie101 on December 02, 2010, 02:49:12 pm: thank u so much
Title: Re: photoelectric emission
Post by: Deadly_king on December 02, 2010, 04:54:59 pm: Quote from: winnie101 on December 02, 2010, 02:49:12 pm
thank u so much

Anytime :)