Question

The figure shows the variation of photo current with anode potential for a photo-sensitive surface for three different radiations. Let $I_a,I_{b}and{I}_c$ and be the intensities and ${\upsilon }_a,{\upsilon }_{b}and{\upsilon }_c$ be the frequencies for the curves a, b and c respectively. Then :

• A. ${\upsilon }_a={\upsilon }_{b}and{I}_a\ne I_b$
• B. ${\upsilon }_a>{\upsilon }_{c}and{I}_a\ne I_c$
• C. ${\upsilon }_a<{\upsilon }_{b}and{I}_a\ne I_b$
• D. ${\upsilon }_b={\upsilon }_{c}and{I}_b\ne I_c$

Answer 1

Answer: (A)

${\upsilon }_a={\upsilon }_{b}and{I}_a\ne I_b$

From the graph, we note that the saturation current is same for curves b and c but different for curve a. Therefore, intensities of b and c will be equal but different from that of a i.e. $I_a\ne I_b$ but $I_b=I_c$. As stopping potential is same for curves a and b, hence ${\upsilon }_a={\upsilon }_b$. Thus answer (a) is correct.