Understanding Stopping Potential in Photoelectric Experiment
What is the work function of the metal surface based on the measurement with green light?
a) Choose one: Approximate 3.03 * 10^19 J
What stopping potential would be observed when using the yellow light from a helium discharge tube?
b) Choose one: Approximately 1.232 x 10^19 volts
Answer:
a) The work function of the metal surface, based on the measurement with green light, is approximately 3.03 * 10^19 J.
b) The stopping potential observed when using the yellow light from a helium discharge tube would be approximately 1.232 x 10^19 volts.
Two light sources are typically used in a photoelectric experiment to determine the work function of a metal surface. In this case, the measurement with green light from a mercury lamp (λ = 546.1 nm) resulted in a stopping potential of 0.376 V, reducing the photocurrent to zero.
Work Function Calculation:
To calculate the work function, we can utilize the equation for the photoelectric effect: \[hf = \phi + eV\]
First, we calculate the frequency of the green light: \[\lambda = 546.1 nm = 546.1 * 10^{-9} m\] \[f = c / \lambda\] \[f = (3 * 10^8 m/s) / (546.1 * 10^{-9} m) = 5.49 * 10^{14} Hz\]
Substitute in the values into the work function equation: \[\phi = (6.626 * 10^{-34} J.s) * (5.49 * 10^{14} Hz) - (1.602 * 10^{-19} C) * (0.376 V)\] \[\phi = 3.03 * 10^{-19} J\]
Therefore, the work function of the metal surface is approximately 3.03 * 10^19 J.
Stopping Potential Calculation:
Stopping potential refers to the potential difference applied across the electrodes to prevent further electron flow in a photoelectric experiment. The stopping potential when using the yellow light from a helium discharge tube can be calculated using the photoelectric effect equation: \[eV = hf - \phi\]
Calculate the frequency of the yellow light: \[f = (3 * 10^8 m/s) / (587.5 * 10^{-9} m) = 5.099 * 10^{14} Hz\]
Now, compute the stopping potential using the equation: \[V = (1/h) * (hf - \phi)\]
Substitute the values for f, Planck's constant (h), and the work function (φ) from the previous calculations to find the stopping potential: \[V = 1.232 x 10^{19} V\]
Therefore, the stopping potential when using the yellow light from the helium discharge tube is approximately 1.232 x 10^19 volts.