Explanation:
(a) Given that,
Area of a parallel plate capacitor, 
The separation between the plates of a capacitor, 
The dielectric constant of, k = 2.1
When a dielectric constant is inserted between parallel plate capacitor, the capacitance is given by :

Putting all the values we get :

(b) We know that the Teflon has dielectric strength of 60 MV/m, 
The voltage difference between the plates at this critical voltage is given by :

or
V = 0.6 kV
Two point charges are on the y axis. A 4.50-σC charge (
) is located at y=1.25 cm (
) , and a -2.24-σC charge (
) is located at y=-1.80 cm (
).
The total electric potential at the origin is
.
How to calculate the total electric potential at the origin?
The total electric potential at some point due to several point charges is represented by:

Here,
(Columbic constant)
The total electric potential at point
is the sum of the potentials due to
and
will be:

Substituting the values, we get:

Hence, the total electric potential at the origin is
.4
To learn more about total electric potential, refer to:
brainly.com/question/16843018
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Frequency measures how many waves pass a certain point in a given amount of time.
High frequency means the waves are closer together and more frequent, making for a lower wave length.
Low frequency means the waves are farther apart and less frequent, making for a higher wave length.
So the answer is frequency.