# THE PHOTOELECTRIC EFFECT Homework Help

OBJECTIVES:

1. To demonstrate the photoelectric effect
2. To observe its dependence on the frequency of incident light
3. To use experimental data to obtain a measured value of Planck’s constant
4. To determine the work function of a metal

INTRODUCTION

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The photoelectric effect was discovered in 1887 by the German physicist Heinrich Rudolf Hertz. In connection with work on radio waves, Hertz observed that, when ultraviolet light shines on two metal electrodes with a voltage applied across them, the light changes the voltage at which sparking takes place.

APPARATUS

1. Optical filters, apertures, caps, and screws
2. Mercury light source enclosure
3. Base
4. Cables and cords

PROCEDURE

In the first procedure Ibegun with the relationship between frequency and KE. I collected all the data at the 8mm aperture which resulted in constant intensity.in the third column I recorded the stopping potential for each wavelength.

In the second procedure, I collected data on the 436nm filter keeping frequency constant and varying the intensity for each of the aperture sizes.

In the third procedure, I took all the data using 436nm filter with constant frequency

DISCUSSION

For a given frequency of light, if the voltage between the cathode and anode is equal to the stopping potential, the photocurrent is zero.

When the voltage between the cathode and anode is greater than the stopping voltage, the photocurrent will increase quickly and eventually reach sarturation.the saturated current is proportional to the intensity of the incident light.

Light of different frequencies have different stopping potentials

The slope of a plot of stopping potential versus frequency is the value of the ratio, h/e

The photoelectric effect is almost instantaneous. Once the light shines on the cathode, photoelectrons will be emitted in less than a nanosecond.

 Kmax F 0 10 2 15 4 18 5 20 6 25 8 30

RESULTS/CALCULATIONS

Example, conversion of wavelength to frequency with reference to procedure 1

Voltage=wavelength*frequency

5.0=0.004*frequency

Frequency=5.0/0.004=1250hz

Maximum kinetic energy;

KE=hf-BE

KE=[(6.62*10-34)*1250]-(1.46*10-11) =1.46*10-11j

CONCLUSION

The energy in light comes in small packets is called a quantum of energy or photon.

From this experiment it becomes clear that the low wavelength photons have high energy while the high wavelength photons have relatively low energy

SOURCES OF ERROR

1. Restraints on the Voltage sensor
2. Restraints on the actual apparatus
3. Faulty averages on the stopping potential

REFERENCES

1. Davis, photoelectric Effect Experiment, AJP 29,706-707(1961)
2. Photocell for determining h and housing for the photocell, Leybold, (1967)
3. Laboratory manual

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