Physics 2nd Paper CQ-Cumilla Board-2019

1. A student arranged two coils co-axially as in the figure below. When there is a current flow in first coil only then he got the magnetic field of $9.42 \times 10^{-4} \mathrm{~T}$ at the center of the coil. He took the number of turns of $2^{\text {nd }}$ coil 450 . After that same current is flown through both the coils and a charge of $80 \mathrm{C}$ is moved with a velocity of $10 \mathrm{~ms}^{-1}$ along the diameter of the coil.

2. A bi-convex lens of $25 \mathrm{~cm}$ focal length and same radius of curvature was made in a lens manufacturing factory. Whose refractive index is 1.6. Then it is used as a mannifying glass in medium of refractive index of $1.16,1.33$ and 1.4 respectively.

3. In Young's double slit experiment the distance between two slits is $0.4 \mathrm{~mm}$ and the distance of screen is $1 \mathrm{~m}$. If the light of wavelength of $3100 \AA$ is passed through the slit then 12 bright fringes are seen on screen in both right and left side from the center of the screen. If the distance between two slits is decreased, the change of fringe on screen is observed.

4. There are two resistances of $60 \Omega$ each are added with the electric source of $120 \mathrm{~V}$ as series circuit. Later on those two resistances are added in parallel to each other and then added with same source.

5. In above circuit $C_{1}$ and $C_{2}$ are two parallel plate capacitors. The distance between two plates and the capacitance of both capacitor are $0.5 \mathrm{~cm}$ and $600 \mathrm{PF}$ respectively. Later on the capacitor $C_{1}$ is filled up with paper $(\mathrm{k}=3.5)$ and a plate similar to the parallel plate is placed exactly in the middle of the capacitor $\mathrm{C}_{2}$.

$\epsilon_{0}=8.85 \times 10^{-12} \mathrm{C}^{2} \mathrm{~N}^{-1} \mathrm{M}^{-2} \text {. }$