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(B) The intensity $I$ of a light beam is defined as the energy incident per unit area per unit time. Since the intensities are equal $(I_A = I_B)$,the

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$\lambda_A / \lambda_B$

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(B) The intensity $I$ of a light beam is defined as the energy incident per unit area per unit time. Since the intensities are equal $(I_A = I_B)$,the power $P$ incident per unit area is the same for both beams.The number of photons incident per unit time is given by $N = P / E$,where $E = hc / \lambda$ is the energy of a single photon.Thus,$N = P\lambda / hc$.Since the number of photoelectrons emitted is directly proportional to the number of incident photons (assuming each photon ejects one electron),the ratio of the number of photoelectrons emitted by beam $A$ to that by beam $B$ is:$\frac{N_A}{N_B} = \frac{P_A \lambda_A / hc}{P_B \lambda_B / hc} = \frac{\lambda_A}{\lambda_B}$ (since $P_A = P_B$).

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