Sound waves are changes in pressure generated by vibrating molecules. The physical characteristics of sound waves influence the three psychological features of sound: loudness, pitch, and timbre. Loudness depends on the amplitude,or height, of sound waves. The greater the amplitude, the louder the sound perceived.
        
                    
             
        
        
        
Answer:
2.083 V.
Explanation:
 Stopping potential is the potential that is required to stop the current to zero . This potential is applied externally to oppose the potential created by the photoelectric effect . It gives the measure the photoelectric potential being generated . 
 Here current drops to 25 μA to 19 μA by a potential of 500mV
Change in current 
= 25 - 19 = 6 μA 
Voltage requirement for unit reduction in current 
= 500 / 6 μA
To reduce current 0f 25 μA 
requirement of V = (500 / 6 )  x 25 =   2083.33 mV = 2.083 V.
 
        
             
        
        
        
Answer:
0.8s
Explanation:
Given parameters: 
Height of shelf  = 3m 
Unknown: 
Time it will take to hit the ground  = ? 
Solution: 
To solve this problem, we use the expression below; 
          x  = ut +  gt²
 gt²  
x is the height
u is the initial velocity  = 0m/s 
g is the acceleration due to gravity  = 9.8m/s² 
t is the time taken  = ?
Now insert the parameters and solve for t; 
     3  = (0 x t) +(  x 9.8 x t²)
 x 9.8 x t²)
     3 = 4.9t² 
        t² = 0.6
        t = 0.8s
 
        
             
        
        
        
<span>The correct answer is C) a motor. 
In particular, we are talking about an AC motor, which produces an alternating current. In an AC motor, a coil is immersed in a rotating magnetic field. Due to the motion of the magnetic field,the angle between the direction of the field and the surface enclosed by the coil changes. As a result, the magnetic flux through the coil changes over time (the magnetic flux is given by:
</span>

<span>
where B is the intensity of the magnetic field, A is the area enclosed by the coil and </span>

<span> is the angle between the direction of B and the perpendicular to the plane of the coil). For Faraday-Newmann-Lenz law, this change in flux induces an electromotive force (emf) into the coil, according to:
</span>

<span>
 where the numerator is the variation of magnetic flux and dt is the time interval. This emf in the coil produced an electrical current in the circuit.</span>