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STUDY OF PHOTOELECTRIC EXTERNAL EFFECT DETERMINATION of PLANCK’S CONSTANT by RETARDING FIELD METHOD
| The purpose of the work: - to study photoelectric external effect laws; - to measure retarding field at different values of falling light frequency; - to calculate Planck’s constant, electron work function, photoelctric threshold for given photocathode | Devices and accessories: 1. optical bench; 2. vacuum photosensitive device ÑÖÂ-4; 3. source of light with changeable light filters; 4. direct current battery; 5. potentiometer; 6. switch; 7. digital devices Ù431Ç ³ Ù4316 for voltage and current measurement |
Task 1. Measurement of stopping potential
1.1. Measure stopping potential at different values of falling light frequency. Enter the results into table 1. Table 1
| Light filters color | U, V | 0,00 | 0,05 | 0,10 | 0,15 | 0,20 | 0,25 | 0,30 | 0,35 | 0,40 | 0,45 | 0,50 | 0,55 | 0,60 | 0,65 |
| Orange λ = __________m | ³, μÀ | ||||||||||||||
| Yellow λ = _________ m | ³, μÀ | ||||||||||||||
| Green λ = _________ m | ³, μÀ | ||||||||||||||
| Blue λ = _________ m | ³, μÀ | ||||||||||||||
| Violet λ = _________ m | ³, μÀ |
Task 2. Plot graphs of functions 
for each light filter.
Task 3. Determine stopping potential 
for each light filter by extrapolation of straight line part of the graph to the its intersection with axis ÎX.
Task 4. Plot the graph of function 
.
Task 5. Planck’s constant determination
5.1. Determine Planck’s constant using the graph of function and according to the formula:
where 
5.2. Enter the results into table 2.
5.3. Determine deviation of measured value of Planck’s constant from theoretical one:
Table 2
| Light filter color | n, Hz |  V
| Planck’s constant, h, J∙s | Deviation of measured value from theoretical one | Work function,  J
| Photoelectric threshold  , Hz
|
| Orange | ||||||
| Yellow | ||||||
| Green | ||||||
| Blue | ||||||
| Violet |
Task 6. Determine work function 
and photoelectric threshold 
for given photocathode using graph of function and formulae:
.
Enter the results into table 2.
Task 7. Determine photoelectric threshold for elements with known work function and plotted graph 
Enter the results into table 3.
Table 3
| Element |  åV
|  , Hz
| Element | åV
| , Hz
|
| Caesium | 1,9 | Potassium | 2,2 | ||
| Natrium (sodium) | 2,3 | Calcium | 2,7 |
Conclusions
The data of laboratory work fulfilment
Pass mark Signature
Mark of laboratory work defence Signature
questions to be admitted for doing laboratory work and its defending
1. What is photoelectric effect?
2. What types of photoeffect do you know?
3. What regularities of photoeffect do you know?
4. What is the essence of photo-electric effect theory?
5. Write down Einstein’s equation for photoeffect and explain it.
6. Formulate external photoelectric effect laws.
7. What is the essence of quantum theory of light?
8. What is photon? Write down its characteristics.
9. What is electron work function?
10. What is stopping potential?
11. What does stopping potential depend on?
12. What is photoelectric threshold?
13. What does photoelectric threshold depend on?
14. Application of photo-electric effect in science and technique.
15. Structure and operation principle of photocell. Integral and spectral sensitiveness of photoeffect.
16. What do energy and speed of electron flown out from photocathode depend on?
LABORATORY WORK
Date: 2015-01-12; view: 1826
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