Light of frequency 1.5 times the threshold frequency is incident on photo-sensitive material.If the frequency is halved & intensity is doubled,the photo current becomes
1. Quadrupled
2. Doubled
3. Halved
4. Zero
Actually, it will depend upon how the quantum efficiency of the photosensitive material varies with frequency. The "quantum efficiency" almost always depends upon wavelength (and therefore frequency), especially near the threshold for the photelectric effect.
In this case, you have a kind of trick question, and an easy answer. Since you halve the frequency and you started out at 1.5 times the threshold frequency, you end up below (at 3/4 of) the threshold frequency for photoelectron emission, and the photocurrent is ZERO.
To determine the effect of changing the frequency and intensity of light on the photo current, we need to understand the concepts of threshold frequency and the photoelectric effect.
The photoelectric effect states that when photons of sufficient energy (based on their frequency) strike a photo-sensitive material, they can cause the ejection of electrons, creating a photo current. The minimum frequency required to initiate this effect is called the threshold frequency.
Now, let's analyze the problem step by step:
1. Light of frequency 1.5 times the threshold frequency is incident on the photo-sensitive material.
- Since the frequency of the incident light is higher than the threshold frequency, electrons will be ejected, and a photo current will be generated.
2. If the frequency is halved and intensity is doubled:
- Halving the frequency means that the frequency of the incident light is now below the threshold frequency.
- Therefore, no electrons will be ejected, as the energy of the incident photons is now lower than the threshold energy. Consequently, the photo current will be zero.
So, the answer to the question is option 4: Zero.