Explanation:
The time taken by a wave crest to travel a distance equal to the length of wave is known as wave period.
The relation between wave period and frequency is as follows.
 T = \frac{1}{f}T= 
f
1
 
 
where, T = time period
 f = frequency
It is given that wave period is 18 seconds. Therefore, calculate the wave period as follows.
 T = \frac{1}{f}T= 
f
1
 
 
 or, f = \frac{1}{T}f= 
T
1
 
 
 = \frac{1}{18 sec} 
18sec
1
 
 
 = 0.055 per second (1cycle per second = 1 Hertz)
or, f = 5.5 \times 10^{-2} hertz5.5×10 −2 hertz
<h3>Thus, we can conclude that the frequency of the wave is 5.5 \times 10^{-2} hertz5.5×10 −2 hertz .</h3>
 
        
             
        
        
        
Solution:
The relation between the potential difference and the electric field between the plates of the parallel plate capacitor is given by :

Differentiating on both the sides with respect to time, we get

Therefore, the rate of the electric field changes between the plates of the parallel plate capacitor is given by :

       
        V/m-s
  V/m-s
 
        
             
        
        
        
<span>Answer: A)	They are isotopes of nitrogen and they contain the same number of protons and electrons but each contains a different number of neutrons - 7 and 8 respectively.
Isotopes are atoms of a chemical element whose nucleus has the same atomic number, Z, but different atomic mass, A. The atomic number corresponds to the number of protons in the atom, therefore the isotopes of an element contain the same number of protons and electrons (atoms have to be neutral particles). The difference in atomic masses arises from the difference in the number of neutrons in the atomic nucleus.
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