Chapter 27, Problem 61A

(a)

To determine

The metal which has higher threshold frequency between potassium and tungsten.

Answer to Problem 61A

Tungsten has higher threshold frequency

Explanation of Solution

Introduction:

Photoelectric effect: It refers to ejection of electron when a radiation having energy greater than the work function of metal is incident on it.

Potassium emits photoelectrons when struck by blue light and tungsten requires ultraviolet radiation for emission of photoelectrons.

Higher threshold frequency means more energy is used to reach the stage where electrons are being knocked off.

As it is mentioned, that ultraviolet light is needed for tungsten to emit photoelectrons and ultraviolet light has higher frequency than blue light, so tungsten metal has higher frequency.

Conclusion:

Tungsten has higher threshold frequency.

(b)

To determine

The metal which has larger work function between potassium and tungsten.

Explanation of Solution

Introduction:

Photoelectric effect: It refers to ejection of electron when a radiation having energy greater than the work function of metal is incident on it.

Potassium emits photoelectrons when struck by blue light and tungsten requires ultraviolet radiation for emission of photoelectrons.

Work function is the energy with which electrons are bounded to the metal.

As ultraviolet light has higher frequency and hence carries more energy, so tungsten requires more energy to emit electrons from the surface and so has higher work function.

Conclusion:

Tungsten has higher work function.