Two metallic plates and

PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Electric Force Field and Potential · Electric Force Field and Potential

Problem

Two metallic plates

A

and

B

, each of area

5\times10^{-4}\text{ m}^2

, are placed parallel to each other at a separation of

1\text{ cm}

. Plate

B

carries a positive charge of

33.7\times10^{-12}\text{ C}

. A monochromatic beam of light, with photons of energy

5\text{ eV}

each, starts falling on plate

A

t=0

so that

10^{16}

photons fall on it per square metre per second. Assume that one photoelectron is emitted for every

10^6

incident photons. Also assume that all emitted photoelectrons are collected by plate

B

and that the work function of plate

A

remains constant at

2\text{ eV}

. Determine the following, neglecting the time taken by a photoelectron to reach plate

B

. Take

\varepsilon_0=8.85\times10^{-12}\text{ C}^2\text{ N}^{-1}\text{ m}^{-2}

. (a) The number of photoelectrons emitted up to

t=10\text{ s}

. (b) The magnitude of the electric field between plates

A

and

B

t=10\text{ s}

. (c) The kinetic energy of the most energetic photoelectron at

t=10\text{ s}

when it reaches plate

B