The correct answer is: A. 1 Photo emissive cathode & 2 dynodes
A photomultiplier is a vacuum tube that uses a series of dynodes to amplify the current produced by a single photon. The first dynode is coated with a material that emits electrons when struck by a photon. These electrons are then accelerated by a voltage difference between the first dynode and the second dynode. When the electrons strike the second dynode, they cause the emission of more electrons, which are then accelerated to the third dynode, and so on. This process of multiplication can be repeated many times, resulting in a large amplification of the original signal.
Photomultipliers are used in a variety of applications, including astronomy, spectroscopy, and medical imaging. They are also used in some types of light meters and photoelectric cells.
Here is a brief explanation of each option:
- Option A: 1 Photo emissive cathode & 2 dynodes. This is the correct answer. A photomultiplier consists of a photoemissive cathode and a series of dynodes. The photoemissive cathode is coated with a material that emits electrons when struck by a photon. The dynodes are coated with materials that emit more electrons when struck by electrons. The electrons emitted by the photoemissive cathode are accelerated by a voltage difference between the cathode and the first dynode. When the electrons strike the first dynode, they cause the emission of more electrons, which are then accelerated to the second dynode, and so on. This process of multiplication can be repeated many times, resulting in a large amplification of the original signal.
- Option B: 2 Photo emissive cathodes & 2 dynodes. This is not the correct answer. A photomultiplier consists of a single photoemissive cathode and a series of dynodes.
- Option C: 2 Photo emissive cathodes & 1 dynode. This is not the correct answer. A photomultiplier consists of a single photoemissive cathode and a series of dynodes.
- Option D: 1 Photo emissive cathode & 1 dynode. This is not the correct answer. A photomultiplier consists of a single photoemissive cathode and a series of dynodes.