Definitions [1]
Definition: Photoelectrons
It is a phenomenon where light falling on a material (usually a metal) causes it to emit electrons, generally called photoelectrons.
Key Points
Key Points: Photoelectric Effect — Hertz's Observations
- Hertz (1887) observed that UV light falling on a metal cathode caused sparks to jump more easily across the gap of his oscillator.
- He noticed high voltage sparks were enhanced when the emitter plate was illuminated with UV light from an arc lamp.
- The phenomenon was later identified as the Photoelectric Effect — emission of electrons when light strikes a metal.
- Hertz also found that maximum spark length was produced when the apparatus was kept in a dark box, confirming light-induced emission.
- Hertz Experiment Setup: Oscillator with brass knobs joined by an induction coil; spark balls separated by a micrometre air gap and a ring receiver.
Key Points: Photoelectric Effect — Hallwachs' and Lenard's Observations
Hallwachs' Observation:
Hallwachs confirmed that UV light incident on a negatively charged zinc plate caused it to lose charge (emit electrons).
Lenard's Observations:
- Lenard measured electron kinetic energy vs light frequency.
- Found: Maximum KE of emitted electrons is directly proportional to the frequency of incident light.
- Changing the intensity of light had no effect on kinetic energy — only on the number of electrons emitted.
- Below a certain threshold frequency (ν₀), no electrons are emitted regardless of intensity.
- The photocurrent was directly proportional to the intensity of the incident light.
- Setup: cathode illuminated with light → electrons travel through vacuum → reach anode → current measured via ammeter.
Important Questions [20]
- Find Threshold Frequency and Incident Frequency
- Draw a Neat Labelled Circuit Diagram of Experimental Arrangement for Study of Photoelectric Effect
- Find the Threshold Wavelength And Maximum Kinetic Energy of Emitted Electrons.
- Find the Maximum Kinetic Energy of the Photoelectrons in Joules.
- The Work Functions for Potassium and Caesium Are 2.25 Ev and 2.14 Ev Respectively. is the Photoelectric Effect Possible for Either of Them If the Incident Wavelength is 5180 å?
- What is Photoelectri Effect ? Defin (I) Stopping Potential (Ii) Photoelectric Work Function.
- If the Total Energy of Radiation of Frequency 10^14 Hz is 6.63 J, Calculate the Number Of Photons In the Radiation.
- Find the Wave Number of a Photon Having Energy of 2.072 Ev
- Calculate the Maximum Kinetic Energy in Ev of Photoelectrons Emitted, When Ultraviolet Light of Wavelength 2600a Falls on It.
- What is the Momentum of a Photon of De Broglie Wavelength 5000 A
- The Planck'S Constant
- Determine the Maximum Kinetic Energy in Joule and in Ev of the Ejects Electron for the Metal Surface When It is Exposed to a Radiation of Wavelength 180 Nm.
- Find the Value of Energy of Electron in Ev in the Third Bohr Orbit of Hydrogen Atom.
- The Energy of Photon of Wavelength X is
- The work function for a metal surface is 2.2eV. If the light of wavelength 5000Å is incident on
- Explain the Observations Made by Hertz and Lenard About the Phenomenon of Photoelectric Emission.
- The Number of Photoelectrons Emitted
- The Momentum Associated with the Photon is Given By____
- If the Work Function of a Metal is 3 Ev, Calculate the Threshold Wavelength of that Metal.
- Draw a Well Labelled Diagram of Photoelectric Cell.
