Question

The work function for the following metals is given Na 2.75 eV; K 2.30 eV; Mo 4.17 eV; Ni 5.15 eV. Which of these metals will not give photoelectric emission for a radiation of wavelength 3300 Å from a He-Cd laser placed 1 m away from the photocell? What happens if the laser is brought nearer and placed 50 cm away?

Answer 1

Hii Dear,

◆ Answer -

1. Mo and Ni will not give photoelectric emission
2. When laser is brought near, intensity of photoelectric emission will increase for Na and K.

● Explaination -

# Given -

λ = 3300 A° = 330 nm

# Solution -

• Energy released by given frequency is calculated by -

E = hc / λ

E = 1242 / 330 eV

E = 3.76 eV

• Photoelectric emission occurs when incident energy is more than that of work function of metal.
• As E is more than Φ in Na (2.75 eV) and K (2.30 eV), these metals will emit photons.
• As E is less than Φ in Mo (4.17 eV) and Ni (5.15 eV), these metals will not show photoemission.

# If laser is brought nearer at 50 cm -

• When laser is brought near at 50 cm, intensity of photoelectric emission will increase for Na and K.
• Energy of incident radiation is unchanged with decrease in distance. Thus even after nearing laser, Mo and Ni will not show photoemission.

Best luck dear...