Table shows the work functions of several different metals. Metal Work function Φ / J Work function Φ / e V Caesium 3 . 0 × 10 - 19 1 . 9 Calcium 4 . 3 × 10 - 19 2.7 Gold 7 . 8 × 10 - 19 4.9 Potassium 3 . 2 × 10 - 19 2.0 Zinc 6 . 9 × 10 - 19 4 . 3 State which metal requires the highest frequency of electromagnetic waves to release electrons.

The work function of a given metal can be defined as the minimum amount of energy which is required to pull out an electron from an atom. This energy is equal to the energy of the electron revolving around the nucleus. Energies that exceed the work function can cause the release of an electron from the metal. Since gold had the maximum value of work function, so it requires the highest frequency of electromagnetic waves to release electrons.

Table shows the work functions of several different metals. Metal Work function Φ / J Work function Φ / e V Caesium 3 . 0 × 10 - 19 1 . 9 Calcium 4 . 3 × 10 - 19 2 . 7 Gold 7 . 8 × 10 - 19 4 . 9 Potassium 3 . 2 × 10 - 19 2 . 0 Zinc 6 . 9 × 10 - 19 4 . 3 State which metal will release electrons when the lowest frequency of electromagnetic waves is incident on it?

The work function of a given metal can be defined as the minimum amount of energy which is required to pull out an electron from an atom. This energy is equal to the energy of the electron revolving around the nucleus. Energies that exceed the work function can cause the release of an electron from the metal. Since caesium had the minimum value of work function, so it requires the lowest frequency of electromagnetic waves to release electrons.

Table shows the work functions of several different metals. Metal Work function Φ / J Work function Φ / e V Caesium 3 . 0 × 10 - 19 1 . 9 Calcium 4 . 3 × 10 - 19 2 . 7 Gold 7 . 8 × 10 - 19 4 . 9 Potassium 3 . 2 × 10 - 19 2 . 0 Zinc 6 . 9 × 10 - 19 4 . 3 Calculate the threshold frequency for zinc.

Threshold frequency is the minimum frequency of the incident radiation below which photoelectric emission is not possible irrespective of the intensity of the incident radiation. Emitted electrons are called photoelectrons. For zinc, threshold frequency is f 0 = ϕ h = 6 . 9 × 10 - 19 6 . 63 × 10 - 34 = 1 . 04 × 10 15 ≈ 1 × 10 15 Hz

Table shows the work functions of several different metals. Metal Work function Φ / J Work function Φ / e V Caesium 3 . 0 × 10 - 19 1 . 9 Calcium 4 . 3 × 10 - 19 2 . 7 Gold 7 . 8 × 10 - 19 4 . 9 Potassium 3 . 2 × 10 - 19 2 . 0 Zinc 6 . 9 × 10 - 19 4 . 3 Calculate the threshold wavelength for potassium.

Threshold frequency is the minimum frequency of the incident radiation below which photoelectric emission is not possible irrespective of the intensity of the incident radiation. Emitted electrons are called photoelectrons. For potassium, threshold frequency is f 0 = ϕ h = 3 . 2 × 10 - 19 6 . 63 × 10 - 34 = 4 . 83 × 10 14 Hz . Since wavelength of light is inversely proportional to its frequency, the threshold wavelength is the maximum wavelength of the light for which the metal will emit electrons. So wavelength is λ 0 = c f 0 = 3 × 10 8 4 . 83 × 10 14 = = ≈ 620 nm .

Electromagnetic waves of wavelength 2 . 4 × 10 - 7 m are incident on the surface of a metal whose work function is 2 . 8 × 10 - 19 J Calculate the maximum kinetic energy of electrons released from the metal. (Use: h = 6 . 63 × 10 - 34 J s )

Energy of a photon is given by E = h ν = h c λ where, h is Planck's constant, ν is the frequency, c is speed of light and λ is wavelength. The energy of a single photon is E = 6 . 63 × 10 - 34 × 3 × 10 8 2 . 4 × 10 - 7 = 8 . 3 × 10 - 19 J . Einstein's photoelectric equation is given by h f = ϕ + K E max here, ϕ = work function and h f = photon energy From above, K E max = h f - ϕ = 8 . 3 × 10 - 19 - 2 . 8 × 10 - 19 = 5 . 5 × 10 - 19 J

Electromagnetic waves of wavelength 2 . 4 × 10 - 7 m are incident on the surface of a metal whose work function is 2 . 8 × 10 - 19 J . Determine the maximum speed of the emitted photoelectrons. (Use: h = 6 . 63 × 10 - 34 J s )

Energy of a photon is given by E = h ν = h c λ where, h is Planck's constant, ν is the frequency, c is speed of light and λ is wavelength. The energy of a single photon is E = 6 . 63 × 10 - 34 × 3 × 10 8 2 . 4 × 10 - 7 = 8 . 3 × 10 - 19 J . Einstein's photoelectric equation is given by h f = ϕ + K E max here, ϕ = work function and h f = photon energy From above, K E max = h f - ϕ = 8 . 3 × 10 - 19 - 2 . 8 × 10 - 19 = 5 . 5 × 10 - 19 J Now, kinetic energy K E max = 1 2 m v 2 ⇒ v = 2 K E max m Putting the values, = 2 × 5 . 5 × 10 - 19 9 . 1 × 10 - 31 = 1 . 1 × 10 6 m s - 1

EASY

AS and A Level

IMPORTANT

Earn 100

Photons of energies $1.0 eV, 2.0 eV & 3.0 eV$ strike a metal surface whose work function is $1.8 eV$ . State which of these photons could cause the release of an electron from the metal.

Important Questions on Quantum Physics

MEDIUM

AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 28 - Quantum Physics>Questions>Q 10

Photons of energies $1.0 eV, 2.0 eV & 3.0 eV$ strike a metal surface whose work function is $1.8 eV$ .

Calculate the maximum kinetic energies of the electrons released in each case. Give your answers in e V and in J.

EASY

AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 28 - Quantum Physics>Questions>Q 11

Table shows the work functions of several different metals.

Metal	Work function $Φ / J$	Work function $Φ / e V$
Caesium	$3.0 \times 10^{- 19}$	$1.9$
Calcium	$4.3 \times 10^{- 19}$	2.7
Gold	$7.8 \times 10^{- 19}$	4.9
Potassium	$3.2 \times 10^{- 19}$	2.0
Zinc	$6.9 \times 10^{- 19}$	$4.3$

State which metal requires the highest frequency of electromagnetic waves to release electrons.

EASY

AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 28 - Quantum Physics>Questions>Q 11

Table shows the work functions of several different metals.

Metal	Work function $Φ / J$	Work function $Φ / e V$
Caesium	$3.0 \times 10^{- 19}$	$1.9$
Calcium	$4.3 \times 10^{- 19}$	$2.7$
Gold	$7.8 \times 10^{- 19}$	$4.9$
Potassium	$3.2 \times 10^{- 19}$	$2.0$
Zinc	$6.9 \times 10^{- 19}$	$4.3$

State which metal will release electrons when the lowest frequency of electromagnetic waves is incident on it?

EASY

AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 28 - Quantum Physics>Questions>Q 11

Table shows the work functions of several different metals.

Metal	Work function $Φ / J$	Work function $Φ / e V$
Caesium	$3.0 \times 10^{- 19}$	$1.9$
Calcium	$4.3 \times 10^{- 19}$	$2.7$
Gold	$7.8 \times 10^{- 19}$	$4.9$
Potassium	$3.2 \times 10^{- 19}$	$2.0$
Zinc	$6.9 \times 10^{- 19}$	$4.3$

Calculate the threshold frequency for zinc.

MEDIUM

AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 28 - Quantum Physics>Questions>Q 11

Table shows the work functions of several different metals.

Metal	Work function $Φ / J$	Work function $Φ / e V$
Caesium	$3.0 \times 10^{- 19}$	$1.9$
Calcium	$4.3 \times 10^{- 19}$	$2.7$
Gold	$7.8 \times 10^{- 19}$	$4.9$
Potassium	$3.2 \times 10^{- 19}$	$2.0$
Zinc	$6.9 \times 10^{- 19}$	$4.3$

Calculate the threshold wavelength for potassium.

EASY

AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 28 - Quantum Physics>Questions>Q 12

Electromagnetic waves of wavelength $2.4 \times 10^{- 7} m$ are incident on the surface of a metal whose work function is $2.8 \times 10^{- 19} J$ . Calculate the energy of a single photon.

MEDIUM

AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 28 - Quantum Physics>Questions>Q 12

Electromagnetic waves of wavelength $2.4 \times 10^{- 7} m$ are incident on the surface of a metal whose work function is $2.8 \times 10^{- 19} J$

Calculate the maximum kinetic energy of electrons released from the metal. (Use: $h = 6.63 \times 10^{- 34} J s$ )

MEDIUM

AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 28 - Quantum Physics>Questions>Q 12

Electromagnetic waves of wavelength $2.4 \times 10^{- 7} m$ are incident on the surface of a metal whose work function is $2.8 \times 10^{- 19} J$ . Determine the maximum speed of the emitted photoelectrons. (Use: $h = 6.63 \times 10^{- 34} J s$ )

Photons of energies 1.0 eV, 2.0 eV & 3.0 eV strike a metal surface whose work function is 1.8 eV. State which of these photons could cause the release of an electron from the metal.

Important Questions on Quantum Physics

Learn and Prepare for any exam you want !

Photons of energies $1.0 eV, 2.0 eV & 3.0 eV$ strike a metal surface whose work function is $1.8 eV$ . State which of these photons could cause the release of an electron from the metal.