JEE Main · 2019 · 11 Jan 2019 · Shift 2 · Modern Physics

WhatsApp Email

In a photoelectric experiment, the wavelength of the light incident on a metal is changed from 300 nm to 400 nm. The decrease in the stopping potential is close to

(\frac{hc}{e} = 1240 nm - V)

(A)0.5 V
(B)1.5 V
(C)1.0 V✓ Correct
(D)2.0 V

Answer: (C)

Solution

The stopping potential comes from

\frac{h c}{λ} = ϕ + e V_{s}

. Writing this for both wavelengths and subtracting,

e (V_{1} - V_{2}) = h c (\frac{1}{λ _{1}} - \frac{1}{λ _{2}})

, so

V_{1} - V_{2} = \frac{h c}{e} (\frac{λ _{2} - λ _{1}}{λ _{1} λ _{2}})

. With

\frac{h c}{e} = 1240

\cdot

λ_{1} = 300

nm and

λ_{2} = 400

nm,

V_{1} - V_{2} = 1240 \times \frac{100}{300 \times 400} = \frac{124000}{120000} \approx 1.0

V, so the stopping potential falls by about

1.0

JEE Main · 2019 · 11 Jan 2019 · Shift 2 · Single correct option

Practise more: all JEE Main PYQs on Modern Physics →

More JEE Main questions on Modern Physics

7.9 MeV α-particle scatters from a target material of atomic number 79. From the given data the estimated diameter of nuclei of the target material is (approximately) ______ m.
[ $\frac{1}{4 π ϵ _{0}} = 9 \times 1 0^{9}$ Nm²/C² and electron charge $= 1.6 \times 1 0^{- 19}$ C]
JEE Main 2026View solution →
The minimum frequency of photon required to break a particle of mass 15.348 amu into $4 α$ particles is ______ kHz.
[mass of He nucleus = 4.002 amu, $1$ amu $= 1.66 \times 1 0^{- 27}$ kg, $h = 6.6 \times 1 0^{- 34}$ J.s and $c = 3 \times 1 0^{8}$ m/s]
JEE Main 2026View solution →
The smallest wavelength of Lyman series is 91 nm. The difference between the largest wavelengths of Paschen and Balmer series is nearly $____$ nm.
JEE Main 2026View solution →
Light is incident on a metallic plate having work function $110 \times 1 0^{- 20} J$ . If the produced photoelectrons have zero kinetic energy then the angular frequency of the incident light is ______ $rad / s$ . ( …
JEE Main 2026View solution →
The energy of an electron in an orbit of the Bohr's atom is $- 0.04 E_{0} eV$ where $E_{0}$ is the ground state energy. If L is the angular momentum of the electron in this orbit and h is the Planck's constant, then …
JEE Main 2026View solution →
A particle having electric charge $3 \times 1 0^{- 19} C$ and mass $6 \times 1 0^{- 27} kg$ is accelerated by applying an electric potential of 1.21 V . Wavelength of the matter wave associated with the particle is $α \times 1 0^{- 12} m$ . The va …
JEE Main 2026View solution →