a sodium photoelectric surface with work function 2.3 ev is illuminated by electromagnetic radiation and emits electrons. the electrons travel toward a negatively charged cathode and complete the circuit shown below. the potential difference supplied by the power supply is increased, and when it reaches 4.5 v, no electrons reach the cathode. (a) for electrons emitted from the sodium surface, calculate the maximum kinetic energy, end the maximum speed. (b) calculate the wavelength of the radiation that is incident on the sodium surface. (c) calculate the minimum frequency of light that will cause photoemission from this sodium surface.

Respuesta :

(a) The highest possible rate of kinetic energy is -2.2 eV and the highest possible rate of speed is 2.3 × 10⁶ m/s.

(b) The length of the radiation's wave is 86 nm.

(c) The lowest frequency of visible light is 3.5 x 10¹⁴ Hz.

SOLUTION

To solve this problem, we can use the following equations:

- The maximum kinetic energy of the electrons emitted from the sodium surface is given by:

KEmax = Work function - Potential difference

- The maximum speed of the electrons is given by:

vmax = sqrt (2 × KEmax ÷ m)

where m is the mass of the electron.

- The incident radiation wavelength can be calculated using the Planck-Einstein equation:

E = h × f

where E is the energy of the incident radiation, h is the Planck constant, and f is the frequency of the radiation.

- The minimum frequency required for photoemission can be calculated using the work function of the sodium surface:

fmin = Work function ÷ h

- Using these equations, we can calculate the following:

(a) The maximum kinetic energy of the electrons is given by:

KEmax = 2.3 eV - 4.5 V = -2.2 eV

Hence,  the maximum kinetic energy is -2.2 eV.

- The maximum speed of the electrons is given by:

vmax = sqrt(2 × (-2.2 eV) ÷ (9.1 × 10⁻³¹ kg)) = 2.3 × 10⁶ m/s

Hence the maximum speed is 2.3 × 10⁶ m/s.

(b) The incident radiation wavelength can be calculated using the Planck-Einstein equation:

E = h × f

f = E ÷ h

f = 2.3 eV / (6.6 × 10⁻³⁴ J × s) = 3.5 × 10¹⁴ Hz

lambda = c ÷ f

lambda = (3.0 x 10⁸ m/s) ÷ (3.5 x 10¹⁴ Hz) = 8.6 x 10⁻⁷ m = 86 nm.

Hence, the wavelength of the radiation is 86 nm.

(c) The minimum frequency required for photoemission can be calculated using the work function of the sodium surface:

fmin = 2.3 eV ÷ (6.6 × 10⁻³⁴ J × s) = 3.5 × 10¹⁴ Hz

Hence, the minimum frequency of light is 3.5 × 10¹⁴ Hz.

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