TG EAMCET 3 May 2025 Shift 2 Paper

The photoelectric effect equation relates the energy of incident photons, the work function of the material, and the maximum kinetic energy of emitted photoelectrons:
E‌photon ‌=φ+KEmax
The maximum kinetic energy ( KEmax ) of the emitted photoelectrons is related to their maximum velocity ( vmax ) by the formula:
KEmax=‌

1

2

mvmax2
The stopping potential (Vs) is the potential difference required to stop the most energetic photoelectrons. The work done by the stopping potential must be equal to the maximum kinetic energy of the electrons:
KEmax=eVs
We are given:
Work function (φ)=1.5eV (Note: This is not directly needed to find the stopping potential if vmax is given, but it would be needed to find the photon energy.)
Maximum velocity (vmax)=8×105ms−1
Mass of electron (m)=9×10−31kg
Charge of electron (e)=1.6×10−19C
First, calculate the maximum kinetic energy ( KE‌max ‌ ) using the given maximum velocity:
‌KEmax=‌

1

2

mvmax2
‌KEmax=‌

1

2

×(9×10−31kg)×(8×105ms−1)2
‌KEmax=‌

1

2

×9×10−31×(64×1010)
‌KEmax=‌

1

2

×9×64×10−31+10
‌KEmax=9×32×10−21
‌KEmax=288×10−21J
Now, use the relationship between maximum kinetic energy and stopping potential ( KEmax=eVs ) to find the stopping potential ( Vs ):
‌Vs=‌

KEmax

e

‌Vs=‌

288×10−21J

1.6×10−19C

‌Vs=‌

288

1.6

×‌

10−21

10−19

‌Vs=‌

2880

16

×10−2
‌Vs=180×10−2
‌Vs=1.8V
The stopping potential of the photoelectrons is 1.8 V .
The final answer is 1.8 V .