JEE Advanced 2014 · Paper 2 · Physics Q7

← JEE Advanced 2014 · Paper 2

PhysicsSingle correct+3 / -1Question 7 of 60

A metal surface is illuminated by light of two different wavelengths 248 nm and 310 nm. The maximum speeds of the photoelectrons corresponding to these wavelengths are $u_1$ and $u_2$ , respectively. If the ratio $u_1:u_2=2:1$ and $hc=1240$ eV nm, the work function of the metal is nearly

3.7 eV

3.2 eV

2.8 eV

2.5 eV

Answer and worked solution

Official answer: A

Photon energies. $\dfrac{1240}{248}=5$ eV and $\dfrac{1240}{310}=4$ eV.

Speeds. $K\propto u^2$ , so $K_1=4K_2$ :
$5-\phi=4(4-\phi)\implies3\phi=11\implies\phi\approx3.7\text{ eV}.$

(A)

Topics:Photoelectric effect

← Previous question Next question →

JEE Advanced 2014 · Paper 2, Physics question 7