Effect of Intensity of Light on Photocurrent
Observation that the photocurrent (number of emitted photoelectrons) is directly proportional to the intensity of incident radiation.
What is Effect of Intensity of Light on Photocurrent?
The electric current produced due to the emission of photoelectrons from a surface when light of suitable frequency falls on it.
Key formula / rule: Photocurrent and Intensity Relationship
Key points
- To understand the relationship between light intensity and photocurrent.
- To explain why photocurrent increases with light intensity.
- To differentiate the effect of intensity from the effect of frequency on photoemission.
Common exam trap
Confusing intensity with frequency: Students often incorrectly assume that increasing intensity affects the energy of individual photons, which is incorrect. Frequency determines photon energy.
Definitions
- Term
Photocurrent
- Meaning
The electric current produced due to the emission of photoelectrons from a surface when light of suitable frequency falls on it.
- Term
Intensity of Light
- Meaning
A measure of the energy flux of electromagnetic radiation, typically expressed as power per unit area. In the context of photons, it relates to the number of photons incident per unit area per unit time.
- Term
Threshold Frequency (ν₀)
- Meaning
The minimum frequency of incident radiation below which the photoelectric effect does not occur, irrespective of the intensity of the radiation.
Learning objectives
To understand the relationship between light intensity and photocurrent.
To explain why photocurrent increases with light intensity.
To differentiate the effect of intensity from the effect of frequency on photoemission.
Formulae
- Name
Photocurrent and Intensity Relationship
- Note
Ip is the photocurrent, I is the intensity of incident light, and \ν0 is the threshold frequency.
- Expression
Ip \propto I \quad \text{(for } \ν \ge \ν0\text{)}
- Name
Einstein's Photoelectric Equation
- Note
While not directly about intensity, it's crucial to remember that intensity affects the number of electrons, not Kmax. h is Planck's constant, \ν is frequency, \φ is work function, Kmax is maximum kinetic energy.
- Expression
h\ν = \φ + Kmax
Prerequisites
Understanding of electromagnetic waves and light.
Concept of photons and their energy (E=hν).
Work function of a metal.
Threshold frequency.
Basic understanding of electric current.
Common mistakes
Confusing intensity with frequency: Students often incorrectly assume that increasing intensity affects the energy of individual photons, which is incorrect. Frequency determines photon energy.
Ignoring the threshold frequency condition: The direct proportionality holds only if the incident light's frequency is above the threshold frequency.
Assuming photocurrent increases with intensity indefinitely: While directly proportional, the relationship is within the limits of the experimental setup and the material's properties.
Keywords
Photoelectric effect
Photocurrent
Light intensity
Photon
Threshold frequency
Photoemission
Lenard's observations
Einstein's photoelectric equation
Practice preview
In the context of the photoelectric effect, what does increasing the intensity of incident light primarily signify?…
easy
If the intensity of monochromatic light falling on a photosensitive surface is doubled, while keeping its frequency constant and above the threshold frequency, what happens to the photocurrent?…
easy
Which graph correctly represents the variation of photocurrent (I_p) with the intensity of incident light (I) in a photoelectric experiment, assuming the frequency of light is above the threshold frequency?…
medium