Answer:
Refractive index of unknown liquid = 1.56
Explanation:
Using Snell's law as:
 
Where,  
 is the angle of incidence  ( 65.0° )
  is the angle of incidence  ( 65.0° )
 is the angle of refraction  ( 53.0° )
 is the angle of refraction  ( 53.0° )
 is the refractive index of the refraction medium  (unknown liquid, n=?)
 is the refractive index of the refraction medium  (unknown liquid, n=?)
 is the refractive index of the incidence medium (oil, n=1.38)
 is the refractive index of the incidence medium (oil, n=1.38)
Hence,  
 
Solving for  ,
, 
Refractive index of unknown liquid = 1.56
 
        
             
        
        
        
Answer:By turning the electrical current off
Explanation:Trust me I took the test 
 
        
                    
             
        
        
        
Explanation:
Resonance: Resonance is the phenomenon which occurs when the applied frequency on the object is equal to its natural frequency.
In the given problem, the singing of an opera singer caused a drinking glass to shatter. 
This occurs due to the phenomenon resonance. The applied frequency of the singing of an opera singer on the drinking glass matches with the natural frequency of the drinking glass. It causes a glass to shatter.