Question

The human eye is a complex sensing device for visible light. The optic nerve needs a minimum of 2.0 x 10⁻¹⁷ J of energy to trigger a series of impulses that eventually reach the brain.
(a) How many photons of red light (700. nm) are needed?
(b) How many photons of blue light (475 nm)?

Answer 1

Answer:

No. of Photons (red) = 7.05 No. of Photons

No. of Photons (blue) = 4.78 No. of Photons

Explanation:

v (red) = 3 x 108/700 x 10-9 = 4.28 x 10 power 15 Hz

v (blue) = 3 x 108/475 x 10-9 = 6.31 x 10 power 15 Hz

(a) No. of Photons (red) = E/hv = 2.0 x 10 power -17 / 6.626 x 10 power -34 x 4.28 x 10 power 15

No. of Photons (red) = 7.05 No. of Photons

(b) No. of Photons (blue) = E/hv = 2.0 x 10 power -17 / 6.626 x 10 power -34 x 6.31 x 10 power 15

No. of Photons (blue) = 4.78 No. of Photons