Air and water have a good day
        
             
        
        
        
Answer: Electromagnetic waves (Ultraviolet light, between 100 nm and 380 nm)
Explanation:
Solar cells work by the photoelectric effect, which consists of the emission of electrons (electric current) when light (electromagnetic waves) falls on a metal surface under certain conditions.  
In this sense, the portion of the electromagnetic spectrum this cells use is Ultraviolet light (UV) from the Sun, whose wavelength is approximately between 100 nm and 380 nm.
It is important to note, this is a type of electromagnetic radiation that is not visible to the human eye. 
 
        
             
        
        
        
Place the object in an electronic balance and measure its mass.
Place a measured amount of water in the cylinder.
Place the object in the cylinder so that it’s fully submerged.
Measure the new level of the liquid and subtract the original level. This is equal to the volume of the object.
Density = mass / volume.
        
             
        
        
        
Answer: Chromosphere hope this helps :)