The potential difference between the plates of an air-filled parallel-plate capacitor with a plate separation of 4 cm is 51 V. What is the magnitude of the electric field between the plates of this capacitor

Explanation:

Electric field between plates of a parallel plate capacitor is uniform .

In a uniform electric field , relation between electric field and potential gradient is as follows

electric field = potential gradient               [ E = - dV / dl ]

in the given case ,

dV = 51 V  ,

dl = 4 cm

=  4 x 10⁻² m

E = 51 /  4 x 10⁻²

= 12.75 x 10² V / m

= 1275 V / m

the answer would be a

d. air pressure decreases as altitude increases.