IIT JEE Advanced 2006 Paper 1

From Einstein’s photoelectric equation, we get

hc

λ

= ϕ + eV0
where ϕ is the work function and V0 is the stopping potential:
V0 =

hc

λc

−

ϕ

e

On comparing with y = mx + c, we get the slope
m =

hc

e

= tan θ
• For metal (1):

1

λ01

=

ϕ1

hc

= 0.001
• For metal (2):

1

λ02

=

ϕ2

hc

= 0.002
• For metal (3):

1

λ03

=

ϕ3

hc

= 0.004
Therefore,
ϕ1:ϕ2"ϕ3 = 1 : 2 : 4
For metal (2), the threshold is
λ02 =

hc

ϕ2

=

1000

2

= 500 nm
For metal (3), the threshold is
λ03 =

hc

ϕ3

=

1000

4

= 250 nm
(a) λviolet = 400 nm < λ02.
(b) λviolet ejects photoelectrons from metal (2).
(c) λviolet = 400 nm < λ03.
(d) λviolet cannot eject photoelectrons from metal (3).