Final answer:
When a parallel-plate setup is immersed under water, the potential difference between the plates reduces due to the higher dielectric constant of water, which weakens the electric field between the plates.
Step-by-step explanation:
When a parallel-plate setup is immersed under water, the potential difference between the plates reduces because of the change in the dielectric constant of the medium. The dielectric constant represents how well a material can store electric charges. Water has a higher dielectric constant compared to air, which means it can store more charges. As a result, when the plates are submerged in water, the electric field between them becomes weaker, leading to a decrease in the potential difference.
For example, let's say we have two parallel conducting plates with a potential difference of 10 volts in air. The electric field between the plates is determined by the equation E = V/d, where E is the electric field, V is the potential difference, and d is the distance between the plates. If we then immerse the plates in water, the electric field will decrease due to the higher dielectric constant of water. Consequently, the potential difference between the plates will also decrease.
In summary, when a parallel-plate setup is submerged under water, the potential difference between the plates reduces due to the higher dielectric constant of water, which weakens the electric field between the plates.