A Covers the light-transmissive window of the photoresistor with a black piece of paper. At this time, the pointer of the multimeter remains basically unchanged, and the resistance is close to infinity. The larger the value, the better the photoresistor performance. If the value is small or close to zero, the photoresistor has been burned through and can no longer be used.
B Align a light source with the light-transmitting window of the photoresistor. At this time, the pointer of the multimeter should have a large amplitude swing, and the resistance value is obviously reduced. The smaller the value, the better the photoresistor performance. If the value is large or infinite, it indicates that the open circuit of the photoresistor is damaged and cannot be used any more.
C Align the light-resisting window of the photoresistor with the incident light, and shake it with the small black paper on the upper part of the light-shielding window of the photoresistor to make it intermittently receive light. At this time, the pointer of the multimeter should swing left and right with the shaking of the black paper. If the multimeter pointer is always stopped at a certain position and does not oscillate with the paper, it indicates that the photosensitive material of the photoresistor has been damaged.
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