Determination of h/e by Photocell Procedure, Observations & Calculations, Viva, Result 2023

by

Aim :

To determine h/e by using vacuum photocell.

Apparatus :

h/e kit and DMM.

Determination of h/e by Photocell - Experiment

Procedure :

Credit – Study Adda

  1. Open the lamp side door of the wooden box and let it lie flat. Fit the lamp in to the socket.
  2. Fit the phototube in to the octal socket. Observe that concave surface of the tube faces the window. If not unscrew the base and adjust. The tube side door must be always kept closed.
  3. Connect red wire from the wooden box to red terminal on control unit and black wire to the black terminal. 
  4. Insert the filter plate in to the slit provided on the wooden box. Adjust so that window is blanked. 
  5. Keep output switch in. For position and SET VOLTAGE control in maximum anticlockwise position. 
  6. Switch on control unit and lamp and wait for 10minutes. 
  7. Bring one color filter in front of window by looking from lamp side. Measure forward current on LHS meter for different value of forward voltage. Repeat the procedure for all filters. Note that Yellow and Green filters are less sensitive to mercury.

Determination of Planck’s constant ( To measure stopping potential)

  1. Keep Output switch in REV position and set voltage at minimum. 
  2. Bring Yellow filter in front of window and wait for a minute. Adjust the SET VOLTAGE so that current just change from 0.01 to 0.0. Read this voltage on LHS meter. This is the STOPPING POTENTIAL for the yellow filter. Repeat the procedure for all other filters. Calculate Planck’s Constant As described.

Observation :

Viva Question and Answers [FAQ] :

1. What is photoelectric effect? 

Ans : Emission of electrons from a material when electromagnetic radiation (light) is in incident on it. It was discovered by Albert Einstein.

2. What is LDR? 

Ans : Light dependent resistor. It convert light energy into electrical energy.

3. Working of LDR? 

Ans : Photocell is a resistor that changes resistance depending on the amount of light incident on it. It operates on semiconductor photo conductivity. The passive component is a resistor whose resistance value decreases when intensity of light increases.

4. Why inert gases are filled photocell?

Ans : Inert gases like neon, argon are filled inside the cell to increase the ionisation and thereby increasing the photoelectric current.

5. What is stopping potential? 

Ans : It’s the voltage difference required to stop the ejection of electrons and stop their movement between the plates. Stopping potential is negative. It depend on the frequency of incident radiation but not on its intensity.

6. For which colour stopping potential is more? 

Ans : Blue, since it’s has minimum wavelength.

7. Define threshold frequency? 

Ans : Minimum frequency of incident radiation below which photoelectric effect is not possible.

8. What is work function? 

Ans : It’s the minimum energy required to remove the electron from the material.

9. Application of photocell? 

Ans : Solar cells, Buglar alarm, calculators, camera, lens, etc.

10. Why photodiode is reverse biased? 

Ans : Photodiode is reverse biased because it causes the potential across depletion region to increase and the width of depletion region increases.

11. Define LED? 

Ans : Light emitting diode; it converts electrical energy into light energy.

12. Name the device which is the combination of LED and photocell. 

Ans : Opto coupler 

Read More