Question

Electric power is typically given in units of watts (1 W = 1 J/s). About 95% of the power output of an incandescent bulb is converted to heat and 5% to light. If 10% of that light shines on your chemistry text, how many photons per second shine on the book from a 75-W bulb? (Assume the photons have a wavelength of 550 nm.)

Answer 1

Answer:

9.43×10^17 photons/second

Explanation:

Power output = 75W = 75J/s

Amount of power output converted to light = 0.05×75J/s = 3.75J/s

Amount of light that shines on my Chemistry text = 0.1×3.75J/s = 0.375J/s

E = nhf

Pt = nhf

n/t = P/hf

P = 0.375J/s, h (Planck's constant) = 6.63×10^-34m^2kg/s, f (frequency) = speed of light/wavelength of photons = 3×10^8/500×10^-9 = 6×10^14Hz

n/t = 0.375/(6.63×10^-34 × 6×10^14) = 9.43×10^17 photons/second