17. The reason why viruses can be seen using electron microscope is that the wavelength of electron can be smaller than the size of viruses. Assume an electron microscope has an accelerating voltage of 40 kV. What is the wavelength of the electron? (A) 0.006 nm (B) 0.003 nm (C) 0.06 nm (D) 0.03 nm (E) 0.6 nm.

4. A pendulum is formed by pivoting a long thin rod of length L and mass M about a point on the rod. Apparently, the period (T) of this pendulum (for small oscillations) depends on the position of the pivot. Suppose the pivot is at a distance d from the center of the rod. What d would give a minimum T? (The moment of inertia of a thin rod about its center is ML²/12) (A) L/√6 (B) L/6 (C) L/√12 (D) L/12 (E) None of the above.

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