What is the threshold frequency for the photoelectric effect on lithium (phi= 2.93eV)? What is the stopping potential if the wavelength of the incident light is 400nm?
To determine the threshold frequency for the photoelectric effect on lithium, we can use the equation:
E = h * f
Where:
E is the energy of a photon,
h is Planck's constant (6.626 x 10^-34 J·s),
f is the frequency of the incident light.
The threshold frequency is the minimum frequency required for the photoelectric effect to occur.
The energy of a photon can be calculated using the equation:
E = phi + KE
Where:
phi is the work function of the material,
KE is the kinetic energy of the emitted electron.
Since we are interested in finding the threshold frequency, the kinetic energy (KE) is zero at the threshold. So we can rewrite the equation as:
E = phi
Thus, the threshold frequency can be found by rearranging the equation:
f_threshold = phi / h
Substituting the given values, we have:
f_threshold = 2.93eV / (6.626 x 10^-34 J·s)
Now, to calculate the stopping potential, we can use the equation:
E = eV
Where:
E is the energy of a photon,
e is the elementary charge (1.602 x 10^-19 C),
V is the stopping potential.
We need to convert the wavelength of the incident light to the frequency using the equation:
f = c / λ
Where:
c is the speed of light (3.00 x 10^8 m/s),
λ is the wavelength of the incident light.
Once we have the frequency, we can calculate the energy of the photon. Since the work function is given, we can equate the energy of the photon to the work function plus the kinetic energy of the emitted electron:
E = phi + KE
At the stopping potential, the kinetic energy of the emitted electron is zero. Thus, we can write:
E = phi + 0
= phi
Comparing the equations, we find:
eV = phi
Rearranging the equation:
V = phi / e
Substituting the given values:
V = 2.93eV / (1.602 x 10^-19 C)
Calculating these equations will give you the threshold frequency and stopping potential for the given information.