The path difference between two waves given by the equations

$y_1=a_1 \sin \left(\omega t-\frac{2 \pi x}{\lambda}\right)$ and $y_2=a_2 \sin \left(\omega t-\frac{2 \pi x}{\lambda}+\phi\right)$ is

The sum of two point positive charges separated by a distance of 1.5 m in air is $25 \mu \mathrm{C}$. If the electrostatic force between the two charges is 0.6 N , then the difference between the two charges is

The energy stored in a capacitor of capacitance $10 \mu \mathrm{~F}$ when charged to a potential of 6 kV is

A parallel plate capacitor has plates of area $0.4 \pi \mathrm{~m}^2$ and spacing of 0.5 mm . If a slab of thickness 0.5 mm and dielectric constant 4.5 is introduced in between the plates of the capacitor, then the capacitance of the capacitor is