# I Why an electron gets knocked out of an atom instead of going to a higher energy level

#### Manasan3010

In this article, writer says that when atom is hit by photon it gets excited and expelled out of atom and this can be used to form images.
My questions are:
1. Why didn't the electrons get to a higher energy level, instead of getting knocked out?
2. How do we find the color(frequency of wave) using photoelectric cell?
3. How do we find the intensity of the light using photoelectric cell?

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#### Drakkith

Staff Emeritus
2018 Award
Why didn't the electrons get to a higher energy level, instead of getting knocked out?
The energy it gained was too high. There were no available energy states for that amount of energy that still allowed the electron to be bound to its nucleus. Basically, the 'kick' was too hard and ejected the electron from the atom.

How do we find the color(frequency of wave) using photoelectric cell?
I suppose you could use a spectrograph that has a number of photoelectric cells as its sensor. Or filter the light using various filters and measure the intensity of the light on the cell for each one. There's really no way to measure the frequency of the incoming light using just a photocell.

How do we find the intensity of the light using photoelectric cell?
Measure the voltage and current provided by the cell to find the power, which allows you to find the intensity of the light falling onto the sensor.

#### Manasan3010

The energy it gained was too high. There were no available energy states for that amount of energy that still allowed the electron to be bound to its nucleus. Basically, the 'kick' was too hard and ejected the electron from the atom.

I suppose you could use a spectrograph that has a number of photoelectric cells as its sensor. Or filter the light using various filters and measure the intensity of the light on the cell for each one. There's really no way to measure the frequency of the incoming light using just a photocell.

Measure the voltage and current provided by the cell to find the power, which allows you to find the intensity of the light falling onto the sensor.
Thank You for the simple explanation, So does the digital camera's sensor consists of RGB filtered photocell for each pixel

#### Drakkith

Staff Emeritus
2018 Award
So does the digital camera's sensor consists of RGB filtered photocell for each pixel
Pretty much. Camera sensors are typically CCD or CMOS sensors with a bayer filter installed. A bayer filter is just a series of alternating red, green, and blue filters installed on top of the pixels. The camera's software knows the pattern of the filters and generates a color image by combining adjacent pixels.

"Why an electron gets knocked out of an atom instead of going to a higher energy level"

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