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Question
A photocell is used to automatically switch on the street lights in the evening when the sunlight is low in intensity. Thus it has to work with visible light. The material of the cathode of the photocell is ______.
Options
Zinc
Aluminum
Nickel
Potassium
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Solution
A photocell is used to automatically switch on the street lights in the evening when the sunlight is low in intensity. Thus it has to work with visible light. The material of the cathode of the photocell is potassium.
Explanation:
The photocell is a resistor or sensor which changes its resistance depending on the amount of light it receives.
- Photocells consist of cathodes and anodes where the cathode is photosensitive which emits electrons when light falls on it and the anode collects the electrons emitted by the cathode.
- The element that is used as a cathode should have less ionization energy so that it can emit an electron when subjected to light.
- Potassium has lower ionization energy. Hence it is used in photocells as the cathode.
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