Dual Nature of Radiation and Matter Flashcards
What experiments in the late 19th century established the wave nature of light and contributed to the understanding of electromagnetism?
Maxwell’s equations of electromagnetism and Hertz’s experiments on electromagnetic waves in 1887.
Who discovered X-rays, and in what year?
Roentgen discovered X-rays in 1895.
Who discovered electrons, and in what year?
J. J. Thomson discovered electrons in 1897.
What were the particles discovered by William Crookes in 1870, and what was his hypothesis about them?
Cathode rays; He suggested they consisted of streams of fast-moving negatively charged particles.
Who confirmed William Crookes’ hypothesis about cathode rays, and how did he experimentally determine the speed and specific charge of these particles?
J. J. Thomson confirmed the hypothesis. He applied mutually perpendicular electric and magnetic fields across the discharge tube.
What is the currently accepted value of the charge-to-mass ratio (e/m) of cathode ray particles?
1.76 × 10^11 C/kg.
What is the relationship between the charge on an oil droplet, as observed by Millikan, and the elementary charge?
The charge on an oil droplet was always an integral multiple of an elementary charge, 1.602 × 10^–19 C.
What did Millikan’s oil-drop experiment establish about electric charge?
It established that electric charge is quantized.
What fundamental constituents of matter did J. J. Thomson propose electrons to be, and when?
Electrons; he proposed this in 1897.
For what discovery was J. J. Thomson awarded the Nobel Prize in Physics, and in what year?
He was awarded the Nobel Prize in Physics in 1906 for his discovery of electrons through his theoretical and experimental investigations on the conduction of electricity by gases.
Who discovered the phenomenon of photoelectric emission?
Heinrich Hertz discovered the phenomenon of photoelectric emission during his electromagnetic wave experiments in 1887.
What did Heinrich Hertz observe during his experiments regarding the emitter plate and ultraviolet light?
Hertz observed that high voltage sparks across the detector loop were enhanced when the emitter plate was illuminated by ultraviolet light from an arc lamp.
How did Hertz describe the effect of light on the metal surface?
Hertz observed that light shining on the metal surface facilitated the escape of free, charged particles, now known as electrons.
What happens to electrons near the surface of a metal when light falls on it according to Hertz’s observations?
When light falls on a metal surface, some electrons near the surface absorb enough energy from the incident radiation to overcome the attraction of the positive ions in the material of the surface.
Who investigated the phenomenon of photoelectric emission in detail after Hertz?
Wilhelm Hallwachs and Philipp Lenard investigated the phenomenon of photoelectric emission in detail during 1886-1902.
What did Philipp Lenard observe when ultraviolet radiations were allowed to fall on the emitter plate of an evacuated glass tube enclosing two electrodes?
Lenard observed that when ultraviolet radiations were allowed to fall on the emitter plate of an evacuated glass tube enclosing two electrodes, current flows in the circuit. As soon as the ultraviolet radiations were stopped, the current flow also stopped.
What did Hallwachs observe when he connected a negatively charged zinc plate to an electroscope and illuminated it with ultraviolet light?
Hallwachs observed that the negatively charged zinc plate lost its charge when it was illuminated by ultraviolet light and became positively charged. Further, the positively charged zinc plate was found to be further enhanced when it was illuminated by ultraviolet light.
What happened when ultraviolet light fell on the emitter plate, according to Hallwachs and Lenard, regarding the emission of electrons?
Hallwachs and Lenard observed that when ultraviolet light fell on the emitter plate, no electrons were emitted at all when the frequency of the incident light was smaller than a certain minimum value, called the threshold frequency.
What metals responded only to ultraviolet light to cause electron emission from the surface, according to observations?
Metals like zinc, cadmium, magnesium, etc., responded only to ultraviolet light, having short wavelength, to cause electron emission from the surface.
Which metals were sensitive even to visible light regarding electron emission from their surfaces?
Alkali metals such as lithium, sodium, potassium, caesium, and rubidium were sensitive even to visible light regarding electron emission from their surfaces.
Describe the arrangement used for the experimental study of the photoelectric effect.
The setup consists of an evacuated glass/quartz tube with a photosensitive plate (emitter) C and a metal plate (collector) A. Monochromatic light from a source S passes through a window W, falling on the emitter C. An electric field between plates A and C, maintained by a battery, collects emitted electrons. The potential difference between A and C is adjustable.
What happens to the photocurrent when the intensity of incident light is varied?
Photocurrent increases linearly with intensity, directly proportional to the number of photoelectrons emitted per second.
How does the photoelectric current change with varying positive potential applied to the collector plate A?
Photoelectric current increases with positive potential until saturation, where all emitted electrons are collected. Negative potential decreases the current until a cutoff potential, where no electrons reach A.
How does the stopping potential vary with the frequency of incident radiation?
Stopping potential increases with higher frequencies, as shown in a linear relation. Higher frequencies result in greater maximum kinetic energy of emitted electrons.
What is the significance of the threshold frequency in photoelectric emission?
Below the threshold frequency, no photoelectric emission occurs, regardless of intensity. Different materials have different threshold frequencies and sensitivities to incident light.
What are the key experimental findings of the photoelectric effect?
- Photoelectric current is proportional to incident light intensity.
- Saturation current is intensity-dependent, while stopping potential is not.
- There exists a threshold frequency below which no emission occurs.
- Emission is instantaneous, occurring without time lag even with dim light.
What phenomena of light were explained by the wave picture of light?
The phenomena of interference, diffraction, and polarization were explained by the wave picture of light.
