PHOTOELECTRIC EFFECT - Q12

12) In which phenomenon do you see the inverse photoelectric effect?
Ans: ARTIFICIAL RADIOACTIVITY, because during bombarding, the element used, contains electrons which reacts with the non-radioactive substance which on further emits radiations.

Artificial radioactivity: metal + electrons = radiation
Photoelectric effect: metal + radiation = electrons

PHOTOELECTRIC EFFECT - Q11

11) Interpret thermionic emission in light of photoelectric effect.
Ans: Thermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier using photoelectric effect. This occurs because the thermal energy given to the carrier overcomes the binding potential, also known as work function of the metal. The charge carriers can be electrons or ions. After emission, a charge will initially be left behind in the emitting region that is equal in magnitude and opposite in sign to the total charge emitted. But if the emitter is connected to a battery, then this charge left behind will be neutralized by charge supplied by the battery, as the emitted charge carriers move away from the emitter, and finally the emitter will be in the same state as it was before emission. The thermionic emission of electrons is also known as thermal electron emission.

PHOTOELECTRIC EFFECT - Q10

10) Can you name a recent method of a very accurate determination of Planck’s constant?
Ans: The nine recent determinations of the Planck constant cover five separate methods. Where there is more than one recent determination for a given method, the value of h given here is a weighted mean of the results, as calculated by CODATA.
CODATA 2010 recommended value

PHOTOELECTRIC EFFECT - Q9

9) What do you know about the structure of photovoltaic cell?
Ans: Photovoltaic cell is a cell comprising an electron tube with a photosensitive cathode that emits electrons when illuminated and an anode for collecting the emitted electrons. The voltage between the anode and cathode causes no current in darkness because no electrons are emitted, but illumination excites electrons that are attracted to the anode, producing current proportional to the intensity of the illumination.

PHOTOELECTRIC EFFECT - Q8

8) What is photoelectric cell?
Ans: Photoelectric cell is a cell used to convert light (such as sunlight) to electricity using photoelectric effect. It comprises of an electron tube with a photosensitive cathode that emits electrons when illuminated and an anode for collecting the emitted electrons. The voltage between the anode and cathode causes no current in darkness because no electrons are emitted, but illumination excites electrons that are attracted to the anode, producing current proportional to the intensity of the illumination.

PHOTOELECTRIC EFFECT - Q7

7) What type of material should be chosen for photoelectron emission?
Ans: The materials with low work function like alkali metals such as potassium (2.29eV), Cesium (2.14eV), sodium (2.36eV), Barium (2.6eV) etc.

PHOTOELECTRIC EFFECT - Q6

6) What do you mean by stopping potential/extinction voltage/cut off voltage?
Ans: If the frequency and the intensity of the incident radiation are fixed, the photoelectric current increases gradually with an increase in positive potential on collector electrode until all the photoelectrons emitted are collected. The photoelectric current attains a saturation value and does not increase further for any increase in the positive potential. If we apply a negative potential to plate Q with respect to plate P and gradually increase it, the photoelectric current decreases until it is zero, at a certain negative potential on plate Q. The minimum negative potential given to plate Q at which the photoelectric current becomes zero is called stopping potential or cut off potential. If e is the charge on the electron and Vo is the stopping potential, then the work done by the retarding potential in stopping the electron = eVo, which gives

PHOTOELECTRIC EFFECT - Q5

5) What is the time lag between the arrival of light at a metal surface and the emission of photoelectron?
Ans: The time lag between the arrival of light at a metal surface and the emission of photoelectron is very small, less than a nano second.

PHOTOELECTRIC EFFECT - Q4

4) Define “work-function”.
Ans: Work-function is the minimum energy required to remove a delocalized electron from the surface of the metal. Work function is given by

where f0 is the threshold frequency for the metal and where ℎ is the Planck’s constant.

PHOTOELECTRIC EFFECT - Q3

3) What is photoelectric effect?
Ans: 

• The emission of free electrons from a metal surface when light of sufficient frequency incident on the metal surface is called photoelectric effect. 
• The maximum kinetic energy K(max) of an ejected electron is given by K(max) = ℎf − ϕ where ℎ is the Planck’s constant, f is the frequency of the incident photon and ϕ is the work function of the metal.

PHOTOELECTRIC EFFECT - Q2

2) What are the sources of error in this experiment?
Ans: Sources of errors:

• Distance between source and filter should not be too large or too small.
• Errors in accuracy of amplifier and voltages. 
• Another possible source of error is outside sources of light.
• And many other systematic and random errors creep into our readings in the experiment.

PHOTOELECTRIC EFFECT - Q1

1) What is the value of Planck’s constant?
Ans: