I think the answer is “greenhouse effect”
        
             
        
        
        
Using the formula v=f times lambada
then v=the speed of light. 
and f=what’s we’re looking for
and lambada=the wavelength. 
so then you sub what you have (v and lambada) in the formula. 
then multiply the frequency(f) by the given wavelength and then solve for f
 
        
        
        
Answer:
Explanation:
Potential energy is the energy stored within an object, due to the object's position, arrangement or state
 
        
                    
             
        
        
        
A convex mirror makes a reflected light rays spread out.
        
                    
             
        
        
        
Answer:
B
Explanation:
Water level remains unchanged 
The first thing to realize is that the buoyancy force is the same as, or equal to the weight of the wood, this same force is also the same as or equal to the weight of the water displaced by the wood. In the two cases, the weight of the wood will be unaffected nonetheless, and thus the water level will remain the same. 
Therefore, the answer is B, the water level remains unchanged.