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

most voltage drop calculators want the distance between the source and destination. then internally, they double it so both the source and return wires are calculated. but you need to know which distance the calculator uses so you're not half of what you should be or double what you should be.

most circuit breakers will not take a #6 directly, so the electrician will have to splice on a smaller pigtail. you also have to upsize the grounding wire when you upsized the ungrounded (hot) wire (see note in 250.122). this will preclude using most cable assemblies, as a cable with #6 copper will most likely only have a #10 grounding conductor. you need a #6 grounding conductor if the circuit is 20a. a #8 cable is no better, as it will have a #10 grounding conductor too. but most 20a breakers will take a #8 directly.

in your related post, you didn't say what type of load this is. if it is a light or heater, voltage drop won't be a big issue. if this is a motor, the current needs are huge at startup and the voltage drop can pose a problem. if this is a motor, knowing if the motor is under much load during startup will answer the voltage drop effect (a saw is easier to start than a compressor).