Answer:
7/150
Explanation:
The following data were obtained from the question:
Object distance (u) = 75cm
Image distance (v) = 3.5cm
Magnification (M) =..? 
Magnification is simply defined as:
Magnification (M) = Image distance (v)/ object distance (u)
M = v /u
With the above formula, we can obtain the magnification of the image as follow:
M = v/u
M = 3.5/75
M = 7/150
Therefore, the magnification of the image is 7/150.
 
        
             
        
        
        
Answer:
minimum frequency = 170 Hz 
Explanation:
given data 
One path long = 20 m 
second path long = 21 m 
speed of sound = 340 m/s
solution
we get here destructive phase that is path difference of minimum  
 
here  λ is the wavelength of the wave 
so path difference will be 
21 - 20 =  
  
λ = 2 m 
and 
velocity that is express as
velocity = frequency × wavelength    .............1
frequency  =  
  
minimum frequency = 170 Hz