A cesium photocell, with a steady potential difference of 60V across it, is illuminated by a bright point source of light 50cm away. When the same light is placed 1m away, the photoelectrons emitted from the cell:
Correct answer: A. Are one quarter as numerous
- A. Are one quarter as numerous
- B. Are half as numerous
- C. Each carry one quarter of their previous momentum
- D. Each carry one quarter of their previous energy
Explanation
Intensity decreases with distance squared, I' = I/(2)² = I/4. Photoelectron number is proportional to intensity, reducing to one-quarter.
Report an error
The more specific you are, the faster it gets fixed. A source beats an opinion.
Prefer email? [email protected]
About Dawn of Modern Physics
Classical physics cannot explain blackbody radiation and related observations, leading to Planck’s quantum theory, in which energy is emitted or absorbed in discrete packets. Photons provide the particle model of light, with energy and momentum linked to frequency and wavelength, including the photoelectric effect and its threshold frequency.
Practise Dawn of Modern Physics
739 free Dawn of Modern Physics MCQs from Physics, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Discussion
Stuck on an option, or know a faster way to get there? Ask or explain it here.
No comments yet. Be the first to explain this one.
Exams that ask Physics questions like this
Physics is on 16 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
More Dawn of Modern Physics questions
The surface of a metal is illuminated with light of 400 nm. The kinetic energy of the ejected photoelectrons was found to be 1.68 eV. The work function of the metal is: (hc = 1240 eV.nm)
When photons of energy hv are incident on a photosensitive material of work function hv₀, then:
If the rate of emission of energy from a star is 2.7 × 10³⁶ J/sec, the rate of loss of mass in the star will be:
In an experiment, a tungsten cathode with a threshold wavelength of 2300 Å is irradiated by ultraviolet light of wavelength 1800 Å. The maximum energy of emitted photoelectrons will be:
The frequency of incident light falling on a photosensitive plate is doubled, then the maximum kinetic energy of the emitted photoelectrons will become:
Stopping potentials of 24, 100, 110, 115 kV are measured for photoelectrons emitted from a certain element when irradiated with monochromatic X-rays. The element is used as a target in an X-ray tube. The energy of the K line is: