Amonochromatic light beam is incident on a barium target that has a work function of 2.50 ev. if a potential difference of 1.00 v is required to turn back all the ejected electrons, what is the wavelength of the light beam? a) 355 nmb) 497 nmc) 744 nmd) 1.42 pme) none of those answers

b) 497 nm

Explanation:

Given:

Work function, ϕ = 2.50 eV

Stopping Potential, V₀ = 1.00 eV

Charge of electron, e = 1.6 x 10⁻¹⁹ C

Speed of light, c = 3 x 10⁸ m/s

Planck's constant, h = 6.63 × 10⁻³⁴ Js = 4.14 × 10⁻¹⁵ eVs

Einstein photoelectric equation  is given by:

                                    = E - ϕ                 ----- (1)                  

is the maximum kinetic energy

E is the energy of the absorbed photons:  E = hf

ϕ is the work function of the surface:  ϕ = hf₀

The potential difference required to back all ejected electrons is called the Stopping Potential (V₀)

                       Stopping Potential (V₀)

                                                -----(2)

Substituting (2) into (1)

                                        eV₀ = E - ϕ

                                      1.6 x 10⁻¹⁹ x 1 = E - 2.50

                                      E = 1.6 x 10⁻¹⁹ + 2.50

                                      E = 2.50 eV

But E = hf = hc/λ

                                     λ

                                     λ = (4.14 × 10⁻¹⁵ × 3 x 10⁸) / 2.50

                                     λ = 1240 × 10⁻⁹ / 2.50

                                     λ = 496.8 × 10⁻⁹ m

                                     λ = 497 × 10⁻⁹ m  (approximately)

                                     λ = 497 nm

the answer is 12 as i may remember

: )

it's a b and