4. If we superimpose two sound waves with frequencies 400Hz and 402Hz, respectively, what is the resulting beat frequency? (A) 2Hz (B) 4Hz (C) 401Hz (D) 160800Hz (E) 401/(2π)Hz.

10. An electric dipole consists of two opposite charges, each with mass m and charge ±q (respectively), and the two charges are separated by a distance d. Under a uniform external electric field E, the electric dipole performs simple harmonic oscillation if the angle between the dipole and E is small. The period of this oscillation is (A) (B) (C) (D)(E) none of the above.

4. If we superimpose two sound waves with frequencies 400Hz and 402Hz, respectively, what is the resulting beat frequency?
(A) 2Hz
(B) 4Hz
(C) 401Hz
(D) 160800Hz
(E) 401/(2π)Hz.

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