The red border of the photoelectric effect is 9nm. what is the maximum kinetic energy of the emitted photoelectrons

| September 23, 2021 | education

The red border of the photoelectric effect is 9nm. what is the maximum kinetic energy of the emitted photoelectrons, if the red border of the photoelectric effect is 1.3 times the wavelength that caused the photoelectric effect

λcr = 3 * λ.

λcr = 9 nm = 9 * 10 ^ -9 m.

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

C = 3 * 10 ^ 8 m / s.

Ek -?

The energy of the incident photons Eph goes to knock out electrons from the surface of the metal Av and impart kinetic energy E to them: Eph = Av + ​​Ek.

Ek = Eph – Av.

The photon energy Eph is expressed by the formula: Eph = h * C / λ = 3 * h * C / λcr, where h is Planck’s constant, C is the speed of light, λ is the photon wavelength, λcr is the red border of the photoelectric effect.

Eph = 3 * 6.6 * 10 ^ -34 J * s * 3 * 10 ^ 8 m / s / 9 * 10 ^ -9 m = 6.6 * 10 ^ -17 J.

We will express the work function of Av to pull out electrons from the metal surface by the formula: Av = h * C / λcr.

Av = 6.6 * 10 ^ -34 J * s * 3 * 10 ^ 8 m / s / 9 * 10 ^ -9 m = 2.2 * 10 ^ -17 J.

Ek = 6.6 * 10 ^ -17 J – 2.2 * 10 ^ -17 J = 4.4 * 10 ^ -17 J.

Answer: with the photoelectric effect, electrons can have a maximum kinetic energy Ek = 4.4 * 10 ^ -17 J.



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