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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: 1595

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