A metal has a threshold wavelength of 6000 A o . Calculate the threshold frequency and the work function of the metal in e V .

Given the threshold wavelength= λ = 6000 × 10 - 10 m The wavelength and frequency is related by the relation ν = c λ where c = velocity of the light.Substituting the values in the formula, we have ν = 3 × 10 8 6000 × 10 - 10 = 5 × 10 14 Hz The work function will be the energy corresponding to this wave length, which is given by W = hν = 6 . 63 × 10 - 34 × 5 × 10 14 1 . 6 × 10 - 19 = 2 . 06 eV

Photoelectric threshold frequency of an alkali metal is 5 . 0 × 10 14 Hz . Calculate the work function of this metal.

Given threshold frequency ν 0 = 5 . 0 × 10 14 Hz The work function of a metal is given by ϕ 0 = h ν 0 , where h = Planck's constant. Substituting the values ϕ 0 = 6 . 62 × 10 - 34 × 5 × 10 14 = 33 . 1 × 10 - 20 J or ϕ 0 = 33 . 1 × 10 - 20 J 1 . 6 × 10 - 19 = 2 . 06 e V

Calculate the work function of sodium metal in electron-volt, if the photoelectric threshold wavelength is 5400 A o . Will photoelectrons be emitted, if red light of wavelength 6800 A o be incident on sodium?

The work function is defined as the energy required to eject electrons from the metal surface without imparting any kinetic energy to them. Given the threshold wavelength 5400 ° A Wave length of red light = 6800 ° A The energy of the incident radiations is , E = hν = hc λ = 6 . 63 × 10 - 19 × 3 × 10 8 5400 × 10 - 10 × 1 . 6 × 10 - 19 = 2 . 3 eV . As the given radiations ( 6800 ° A ) have more wave length, its energy will be less than the work function of the metal, hence the photo emission is not possible.

E M B I B E

ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 17

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The work function for sodium is $2.28 e V$ . What is the minimum energy for a quantum of radiation to cause photoelectric emission from a sodium surface?

Important Questions on Photoelectric Effect

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IMPORTANT

ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 17

The work function for sodium is

2.28 eV

. Calculate the wavelength of this radiation?

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ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 18

A metal has a threshold wavelength of

6000 \overset{o}{A}

. Calculate the threshold frequency and the work function of the metal in

e V

.

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ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 19

Photoelectric threshold frequency of an alkali metal is

5.0 \times 10^{14} Hz

. Calculate the work function of this metal.

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ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 20

Calculate the threshold frequency of photon for photoelectric emission from a metal whose work function is

0.1 e V

.

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ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 21

The work function of sodium is

2.28 e V

. Calculate the maximum wavelength in

nm

(nanometre) for the light that will cause photoelectrons to be emitted from sodium.

(h = 6.63 \times 10^{- 34} Js)

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ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 22

If the work function of a certain metal is

4.2 e V

, will radiation of wavelength

330 nm

incident on the surface emit electrons? Confirm it by calculation.

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ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 23

The work function of copper metal is

4 e V

. Monochromatic light of wavelength

4000 \overset{o}{A}

falls upon it. Calculate the energy of the incident photon in joule. Also, express the work function in joule. Find out the kinetic energy of the fastest electron ejected from it.

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ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 24

Calculate the work function of sodium metal in electron-volt, if the photoelectric threshold wavelength is