A constant potential difference is applied between two horizontal metal plates. A charged oil droplet is held stationary by the electric field between the plates. [Figure showing a charged oil droplet between two horizontal metal plates] As some of the oil evaporates, the droplet loses mass and starts to accelerate. Its charge remains constant. In which direction does the droplet accelerate, and which change needs to be made to the separation of the plates in order to stop this acceleration?

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