4. The sound of a whisper is around 20 decibels. How many people would need to be whispering for the total sound to be 50 decibels?

A. 10-7 B. 2.5 C. 30 D. 1000 E. 1030

5. How much energy is stored by the electric field between two square plates, 7.7 cm on a side, separated by a 2.1-mm mm air gap? The charges on the plates are equal and opposite and of magnitude 17 nC .Express your answer using two significant figures and include the appropriate units.