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A 25 What bulb emits monochromatic yello...

A 25 What bulb emits monochromatic yellow light of wavelength of `0. 75 um.` Calculate the rate of emission of quanta per second.

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We know that
Energy of one photon
`E = hv =( hv)/(lamda ) because v = (c)/( lamda )`
wher `h = 6.626 xx 10 ^(-34) Js`
`C = 3. 0 xx 10 ^(8) m`
`lamda = 0. 57 mu m 1 mu m = 10 ^(-6) m`
`lamda = 0. 57 xx 10 ^(-6) m`
`E = ( 6.6 3 xx 10 ^(-34) xx 3. 0 xx 10 ^(8))/( 0. 57 xx 10 ^(-6))`
`E = 3. 478 xx 10 ^(-19) J`
Now, 25 Watt = 25 J/s
`therefore ` Number of phtons emitted per second `= (25)/( 3. 487 xx 10 ^(-19)) = 7.17 xx 10 ^(-19) s ^(-1)`
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