Photoelectric effect and experimental setup

Photoelectric effect and experimental setup and proof.

1. Photo-Electric Effect. -MIT- AOE F.Y B.TECH Physics (Applied Science) Group -D7 Theoretical & Experimental Explanation For Topic .

2. Group D7 Members Group D7 Members are as FOLLOWS: - Omkar RANE , ROLL NO: - 422 (BATCH D1) Prashant Mungase , ROLL NO :-427 (batch d1) mehul JOSHI , ROLL NO: - 429(batch D2) Jamir SHEIKH , roll NO: - 434(batch d2) vikram KARE , roll NO: - 418(batch d1)

3. Time-line of Photoelectric effect development The photoelectric effect was first observed in 1887 by  Heinrich Hertz  (1857–1894) during experiments with a spark-gap generator (the earliest form of radio receiver). It was   Philipp Lenard   1862, an assistant of Heinrich Hertz , who performed the earliest, definitive studies of the photoelectric effect. It was the vacuum tube experiment in which radiation was incident on photosensitive plate . As soon as the light was incident, photo electrons were received at collector plate this caused electric current to flow through circuit. In 1905 , Albert Einstein realized that light was behaving as if it was composed of tiny particles (initially called quanta and later called photons) and that the energy of each particle was proportional to the frequency of the electromagnetic radiation. He also derived equation which explained the characteristics of photoelectric effect satisfactorily.

4. - Heinrich Hertz, in 1887, made observations of the photoelectric effect and of the production and reception of electromagnetic (EM) waves. -His receiver consisted of a coil with a spark gap, whereupon a spark would be seen upon detection of EM waves. He placed the apparatus in a darkened box in order to see the spark better; he observed, however, that the maximum spark length was reduced when in the box -When removed, the spark length would increase . Hertz found that he could increase the sensitivity of his spark-gap device by illuminating it with visible or ultraviolet light.   SPARK GAP EXPERIMENT

5. The intensity of the incident light had no effect on the maximum kinetic energy of the photoelectrons. Those ejected from exposure to a very bright light had the same energy as those ejected from exposure to a very dim light  of the same frequency . In keeping with the law of conservation of energy, however, more electrons were ejected by a bright source than a dim source. VACCUM TUBE EXPERIMENT

6. The Photoelectric Effect Equation A photon is absorbed by an electron in a metal surface causing an electron to be emitted. (E) Energy of photon = h*f Energy is conserved, “f” is the frequency , “h” planks constant   h=6.626 × 10 −34  js Only electrons with energy above the work function energy will be emitted. Only light with a frequency greater than the threshold frequency will cause emission Energy=work function + Max KE of electron. E=h ν−Φ or K.E=h ν−Φ The minimum quantity of energy which is required to remove an electron to infinity from the surface of a given solid, usually a metal. Number of electrons emitted depends on light intensity.

7. Energy of a Photon How do you calculate the energy of a photon ?

8. Experimental Verification Of Photoelectric effect. Photo-Electric Effect and Its verification: - Requirements: - Gold leaf electroscope /alternative aluminium foil electroscope, Pure Zinc Metallic Plate, U.V source of light, Ebonite Rod for charging electroscope with negative charge, Silk Cloth for rubbing ebonite rod, etc. Timeline: - 1-month Duration.  

9. Making of aluminium Foil Electroscope

10. Method of Inductive charging http://rimstar.org/science_electronics_projects/photoelectric_effect.htm

11. The Photoelectric Effect Describe the Photoelectric Effect Experiment Step1)Use Aluminium foil electroscope Step 2) Removing zinc oxide layer from zinc plate Step 3) Placing the zinc plate on electroscope Step 4) Charging By Inductive Method Step 5) Putting the UV lamp in place

12. Observations On Inductive Charging After U.V Light exposure Negatively charged electroscope. An electron leaving the metal plate . Uncharged electroscope - done.

13. How the photoelectric effect works? The photoelectric effect is an effect where electrons are emitted from certain materials when light of a certain minimum wavelength arrives at the material. A photon is emitted from a light source to a metal plate . Photons are electromagnetic waves and have a specific wavelength and that wavelength indicates how much energy the photon has. The shorter the wavelength, the greater the energy's we have U.V source of light for experiment . For the photoelectric effect to happen, the photon must have enough energy to overcome the work function of whatever atom the metal is made of plus some extra kinetic energy. The work function is the amount of energy needed to break the electron free of the atom. Different atoms have different work functions (required amounts of energy.) Zinc's work function is 4.3eV (eV stands for electron volt and is a unit of energy.) . UV light is light whose wavelength is somewhere in the range 280nm to 315nm (nm is nanometres) which equates to energy of 3.94eV to 4.43eV. Notice that above I said zinc's work function is 4.3eV, which is in the UV-light range. i.e. When a UV light with an energy of 4.43eV arrives at a zinc atom, 4.3eV of it will go to freeing an electron from the atom with 0.13eV left over for the electron to move away (4.43eV - 4.3eV = 0.13eV).

14. Why do the leaf's of the electroscope come together? After turning on the UV lamp you first inductively charge the electroscope such that it has a negative charge on that there are more negative electrons on the electroscope than positive protons. That causes the leaf's to be spread apart. Then, as just stated above, after you turn on the UV lamp, the photoelectric effect removes electrons from the metal plate which is in contact with the electroscope, thereby removing electrons from the electroscope. If you wait long enough all of the extra negative electrons will be removed and since the electroscope will no longer be negatively charged, the leaf's will come back together again.

15. Outcomes Of Experiment:-   The researchers found four important facts about the experiment: (a) no electrons were emitted from the plate if it was positive (b) the number of electrons emitted per second depended on the intensity of the incident radiation (c) the energy of the electrons depended on the frequency of the incident radiation (d) there was a minimum frequency (fo) below which no electrons were emitted no matter how long radiation fell on the surface This minimum frequency is called the threshold frequency for that material. Photons with a lower frequency will never cause electron emission.

16. Video On Experiment Source:- http://www.nationalstemcentre.org.uk/elibrary/search?term=photoelectric+effect&order=score or https://www.stem.org.uk