KVPY Government Jobs Exams

A stream of photons having energy 3 eV each impinges on a potassium surface. The work function of potassium is
2.3 eV. The emerging photo-electrons are slowed down by a copper plate placed 5 mm away. If the potential
difference between the two metal plates is 1 V, the maximum distance the electrons can move away from the
potassium surface before being turned back is

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KVPY Other Question

A radioactive nucleus A has a single decay mode with half life τA. Another radioactive nucleus B has two decay
modes 1 and 2. If decay mode 2 were absent, the half life of B would have been τA/2. If decay mode 1 were absent,
the half life of B would have been 3τA, then the ratio τB/τA is Consider three concentric metallic spheres A, B and C of radii a, b, c respectively where a < b < c, A and B are
connected whereas C is grounded. The potential of the middle sphere B is raised to V then the charge on the sphere
C is–