### Correct Option: B **Explanation of Why Option B is Correct:** The photoelectric effect is a phenomenon where electrons are ejected from a metal surface when it is exposed to light of sufficient frequency. The key points to understand this effect are: 1. **Threshold Frequency**: Each metal has a specific threshold frequency (denoted as \( f_0 \)). This is the minimum frequency of incident light required to eject electrons from the metal surface. If the frequency of the light is below this threshold, no electrons will be emitted, regardless of the intensity of the light. 2. **Photon Energy**: The energy of a photon (the particle of light) is given by the equation: \[ E = hf \] where \( E \) is the energy of the photon, \( h \) is Planck's constant (\( 6.626 \times 10^{-34} \, \text{Js} \)), and \( f \) is the frequency of the light. If the frequency is below the threshold frequency, the energy of the photons is insufficient to overcome the work function (the minimum energy needed to remove an electron from the metal). 3. **Ejection of Electrons**: When the frequency of the incident light is equal to or greater than the threshold frequency, photons can impart enough energy to the electrons to overcome the work function of the metal, resulting in the ejection of electrons. 4. **Kinetic Energy of Ejected Electrons**: The kinetic energy (\( KE \)) of the ejected electrons can be calculated using the equation: \[ KE = hf - \phi \] where \( \phi \) is the work function of the metal. This shows that the kinetic energy of the ejected electrons increases with the frequency of the incident light, provided it is above the threshold frequency. ### Why the Other Options are Incorrect: **Option A: Electrons are ejected only if the intensity of light is high enough, regardless of frequency.** - This statement is incorrect because the photoelectric effect is fundamentally dependent on the frequency of the light, not just its intensity. Increasing the intensity (which means more photons) does not help if the frequency is below the threshold frequency; no electrons will be emitted. **Option C: The number of electrons ejected increases with frequency, regardless of intensity.** - This statement is misleading. While it is true that the number of ejected electrons can increase with intensity (more photons hitting the surface), the frequency must still be above the threshold frequency for any electrons to be emitted at all. Once above the threshold, increasing frequency increases the kinetic energy of the electrons, but not necessarily the number of electrons emitted. **Option D: Higher frequency light causes electrons to be ejected with less kinetic energy.** - This statement is false. Higher frequency light actually results in electrons being ejected with greater kinetic energy, as per the equation \( KE = hf - \phi \). As frequency increases, the energy of the photons increases, leading to higher kinetic energy for the emitted electrons. ### Summary of Key Points: - The photoelectric effect requires a minimum threshold frequency for electron ejection. - The energy of incident light is proportional to its frequency, not its intensity. - Electrons are ejected with kinetic energy that increases with frequency above the threshold. - Intensity affects the number of electrons emitted, but not their kinetic energy if the frequency is above the threshold. This understanding of the photoelectric effect is crucial for grasping concepts in quantum physics and the behavior of light as both a wave and a particle.