A horizontal cesium plate`(phi=1.9eV)` is moved vertically downward at a constant speed v in a room full of radiation of wavelength 250nm and above. What should be the minimum value of v so that the vertically upward component of velocity is nonpositive for each photoelectron?

Explanation

To solve the problem, we need to determine the minimum speed \( v \) of a horizontal cesium plate so that the vertically upward component of the velocity of emitted photoelectrons is non-positive. Here’s a step-by-step solution:

### Step 1: Understand the Problem
We have a cesium plate with a work function \( \phi = 1.9 \, \text{eV} \) and it is exposed to radiation of wavelength \( \lambda = 250 \, \text{nm} \). We need to find the minimum speed \( v \) of the plate such that the emitted photoelectrons do not move upward.

### Step 2: Calculate the Energy of the Incoming Photons
Using the energy of a photon, we can find the energy associated with the radiation of wavelength \( \lambda \):
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