A capacitor of capacity 10 microfarad is charged through a resistance of 100 kilo-ohms by a DC source of 2 volts. The potential difference across the capacitor after 2 sec will be:

a. 1
b. 2
c. 1.73
d. 1.52

The answer is 4f======since electrostatic force is given by    we let f be the electrostatic force when  r = 1 m    if we let  denote the electrostatic force when the distance is decreased so that r = 0.5m, then    we established earlier that f = kq₁q₂. therefore    the force will now be 4f.

Lexy is correct because angle r is between the incident wave,  n  = 0, and a diffracted wave.