The photoelectric effect describes the emission of electrons when light shines on a material. Its characteristics are explained by Einstein's photoelectric equation, which relates the energy of incident photons to the work function of the metal and the kinetic energy of the emitted photoelectrons.
Einstein's Photoelectric Equation: The fundamental equation governing the photoelectric effect is given by:
\[ E = h\nu = \phi + K_{\text{max}} \]Where:
Rearranging for Maximum Kinetic Energy: We can rearrange the equation to express the maximum kinetic energy:
\[ K_{\text{max}} = h\nu - \phi \]Analyzing the effect of increasing frequency: From the rearranged equation, if the frequency \(\nu\) of the incident light increases (assuming it's above the threshold frequency, so photoemission occurs), and \(h\) and \(\phi\) (work function of the metal) are constants for a given metal, then \(h\nu\) will increase. Consequently, \(K_{\text{max}}\) will also increase.
Conclusion: An increase in the frequency of incident light directly leads to an increase in the maximum kinetic energy of the emitted photoelectrons.
Correct Option: C) An increase in the maximum kinetic energy of the emitted photoelectrons
The question asks to identify which characteristic of the photoelectric effect could NOT be explained by classical wave theory and required Einstein's quantum explanation. We need to recall the key features of the photoelectric effect and compare them with the predictions of classical wave theory versus quantum theory.
Therefore, the threshold frequency is the characteristic that classical wave theory failed to explain.
A) The existence of a threshold frequency, below which no photoelectric emission occurs regardless of light intensity — This phenomenon
The question asks about the time delay in photoelectric emission. This phenomenon is best explained by the particle nature of light (photons) and is a key concept in modern physics. We need to recall the fundamental characteristics of the photoelectric effect.
B) Instantaneously, with no significant measurable time delay (consistent with the particle/photon model of light) — This option accurately describes the photoelectric effect. The emission of photoelectrons is an instantaneous process, provided the incident light has a frequency above the threshold frequency for the given metal. This instantaneous nature is a strong piece of evidence supporting the photon (particle) model of light, where energy is transferred in discrete packets.
The question asks about the practical applications of photocells, which operate based on the photoelectric effect. We need to identify the option that correctly describes a common use of these devices.
Correct Option: C) Automatic streetlights and burglar alarm systems, which respond to changes in incident light
The question asks about J.J. Thomson's 'Plum Pudding Model' of the atom. To answer this, we need to recall the key features of this specific atomic model as proposed by Thomson in 1904.
Based on this description, option B accurately reflects Thomson's model.
B) A sphere of uniformly distributed positive charge, with negatively charged electrons embedded within it — This perfectly describes J.J. Thomson's Plum Pudding Model. He envisioned the atom as a positive "pudding" with negative "plums" (electrons) scattered throughout, ensuring overall electrical neutrality.
The question asks about the discovery resulting from Ernest Rutherford's gold foil experiment. This experiment, also known as the Geiger-Marsden experiment, was crucial in understanding the structure of the atom. We need to recall the observations and conclusions drawn from this landmark experiment.
Correct Option: D) The atomic nucleus, a small, dense, positively charged core at the centre of the atom