1 A firefly glows by the direct conversion of chemical energ

1.
A firefly glows by the direct conversion of chemical energy to light. Suppose the light emitted by a firefly has peak intensity at a wavelength of 558 nm.
(a) What is the minimum chemical energy, in eV, required to generate each photon?


(b) One molecule of ATP provides 0.30 eV of energy when it is metabolized in a cell. What is the minimum number of ATP molecules that must be consumed in the reactions that lead to one photon of 558 nm light?

2.

Rod cells in the retina of the eye detect light using a photopigment called rhodopsin. Suppose that 2.18 eV is the lowest photon energy that can trigger a response in one such photopigment. What is the maximum wavelength of electromagnetic radiation that can cause a transition?

In what part of the spectrum is this?
radio

microwave     

infrared

visible

ultraviolet

x ray

gamma ray
3.

Suppose you have a 1.00 g sample of 226^Ra, half-life 1600 years. How long will it be until only 0.275 g of radium is left?
6,000 yr

750 yr     

1500 yr

3000 yr
4.

What is the age of a bone in which the 14C/12C ratio is measured to be 1.61 X 10^-13?

5.

A slab of material of thickness 2.0 cm reduces the amount of radiation by a factor of 3.0. How much is the radiation reduced (from its original amount) if you use a 6.0 cm thickness of this material? (Answer by the factor by which it\'s reduced, so your answer should be > 1; e.g., if it\'s cut in 1/2, you would answer 2.)

Solution

1. a) Energy = hc / lambda

= 1240 eV-nm / 558 nm

= 2.22 eV

b) energy by one molecule = 0.30 eV

number of molecule = 2.22 / 0.30 = 7.4 molecules.

2. Energy = hc / lambda

2.18 = 1240 eV-nm / lambda

lambda = 568.8 nm

This wavelength comes into visible spectrum.