In an experiment on photoelectric effect, the emitter and the collector plates are placed at a separation of 10 cm and are connected through an ammeter without any cell figure. A magnetic field B exists parallel to the plates. The work function of the emitter is 2.39 eV and the light incident on it has wavelengths between 400 nm and 600 nm. Find the minimum value of B for which the current registered by the ammeter is zero. Neglect any effect of space charge.

Question

Philoid · Accepted Answer

Given, work function Ф=2.39 eV

Wavelengths

Radius of the path = 10cm =0.1 m

From Einstein’s photoelectric equation,

⇒ …. (1)

Where h is Planck’s constant

c is the speed of light

λ is the wavelength of light

E is the energy (kinetic energy)

Ф is the work function

We know that radius of the path traversed by the particle

In the magnetic field B is given by-

….. (2)

Where m is the mass of an electron

E is the energy

q is the charge on an electron

B is the magnetic field

∴ for B to be minimum energy E should be maximum and for E to be maximum λ should be minimum.

Hence we will consider the smallest value of λ

and put the values in eq (1) we get,

∴

Now, putting the value in eq (2) we get,

∴ Magnetic field,