A photosensitive material would emit electrons if it is excited by a photon beyond a threshold. To cross the threshold, what should be increased?
Correct answer: B. Frequency
- A. Wavelength of light
- B. Frequency
- C. Voltage of source
- D. Intensity of light
Explanation
Einstein's Photoelectric Effect equation is: hf = hfo + KEmax Where hf is the energy of the photon, hfo is the work function of the material, and KEmax is the surplus energy that enables the electron to leave the surface of the material. The work function (hfo) is the minimum or threshold energy required to cause the photoelectric effect. If the energy of a photon is less than hfo, not enough energy would be transmitted to the electron to come up to the surface, and there would be no photoelectric effect. Thus by increasing the frequency and decreasing the wavelength, the threshold for the photoelectric effect can be crossed. The intensity of light does not affect the threshold. It only affects the number of electrons emitted and hence, the photocurrent. The voltage of the source affects current; increasing the positive voltage (when the cathode is negative) increases the current while increasing the negative voltage (when the cathode is positive) decreases the current. At a particular value of negative voltage, called the stopping potential, the current becomes zero.
Last updated
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.
Exams that ask Physics questions like this
Physics is on 13 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
Related questions
1.5 mW of 400 nm light is directed at a photoelectric cell. If 0.1% of the incident photons produce photoelectrons, the current in the cell is:
1.5 mW of 400 nm light is directed at a photoelectric cell. If 0.1% of the incident photons produce photoelectrons, the current in the cell is:
A 5 watt LED bulb converts 80% of the power into light photons wavelength 660 nm. What is the number of photons emitted from the bulb in one second.
A black body is considered ideal when it:
A body at temperature T radiates heat according to relation: