The red border of the photoelectric effect for cesium is 653 nm. To find the speed of photoelectrons

| April 27, 2021 | education

The red border of the photoelectric effect for cesium is 653 nm. To find the speed of photoelectrons knocked out by irradiation of cesium with violet light with a wavelength of 400 nm

λcr = 653 nm = 653 * 10 ^ -9 m.

λ = 400 nm = 400 * 10 ^ -9 m.

h = 6.6 * 10 ^ -34 J * s.

C = 3 * 10 ^ 8 m / s.

m = 9.1 * 10 ^ -31 kg.

V -?

Let us write down the law of the photoelectric effect: h * C / λ = Av + ​​Ek.

The work function of electrons from cesium Av will be expressed by the formula: Av = h * C / λcr.

We express the kinetic energy of electrons Ek, which fly out of the metal surface, by the formula: Ek = m * V ^ 2/2.

h * C / λ = h * C / λcr + m * V ^ 2/2.

m * V ^ 2/2 = h * C / λ – h * C / λcr.

V ^ 2 = 2 * (h * C / λ – h * C / λcr) / m.

V = √ (2 * (h * С / λ – h * С / λcr) / m).

V = √ (2 * (6.6 * 10 ^ -34 J * s * 3 * 10 ^ 8 m / s / 400 * 10 ^ -9 m – 6.6 * 10 ^ -34 J * s * 3 * 10 ^ 8 m / s / 653 * 10 ^ -9 m) / 9.1 * 10 ^ -31 kg) = 6.5 * 10 ^ 5 m / s.

Answer: electrons fly out of the surface of cesium with a speed of V = 6.5 * 10 ^ 5 m / s.



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