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A stream of photons having energy 3 eV e...

A stream of photons having energy 3 eV each impinges on a potassium surface. The work function of potassium is 2.3 eV. The emerging photo-electrons are slowed down by a copper plate placed 5 mm away. If the potential difference between the two metal plates is 1 V, the maximum distance the electrons can move away from the potassium surface before being turned back is–

A

3.5 mm

B

1.5 mm

C

2.5 mm

D

5.0 mm

Text Solution

Verified by Experts

The correct Answer is:
A
Energy of incident beam = 3 eV
`phi =2.3eV`
`K_("max") = 3 - 2.3 = 0.7 eV`
At the point of returning back the entire KE is converted into electrostatic PE
Electric field `(E) =(DeltaV)/(Deltax) =1/5 =0.2 V-mm^(-1)`
`implies e xx 0.2 V xx "x" -0.7 eV =0.7eV`
`implies x = 3.5 mm`
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