An uncharged capacitor is connected to a 21-V battery until it is fully charged, after which it is disconnected from the battery. A slab of paraffin (K= 2.2) is then inserted between the plates. Required:
What will now be the voltage between the plates?

Light from a sodium lamp passes through a diffraction grating that has 1000 slits per millimeter. the interference pattern is viewed on a screen 1.000 m behind the grating. the first (m = 1) two bright yellow fringes that are visible are 0.7288 m and 0.7300 m from the central maximum. what are the wavelengths of these two fringes?