Huygens' wave theory allows us to know the:

When the light diverges from a point source, the shape of the wavefront is:
1. Parabolic
2. Plane
3. Spherical
4. Elliptical

By Huygen's wave theory of light, we cannot explain the phenomenon of:

Which of the following is not true?

Two superposing waves are represented by the following equations: $y_1=5 \sin 2 \pi(10{t}-0.1 {x}), {y}_2=10 \sin 2 \pi(10{t}-0.1 {x}).$ 
The ratio of intensities $\dfrac{I_{max}}{I_{min}}$ will be:
1. $1$
2. $9$
3. $4$
4. $16$

Two sources with intensity $I_0$ and $4I_0$ respectively interfere at a point in a medium. The maximum and the minimum possible intensity respectively would be:
1. $2I_0, I_0$
2. $9I_0, 2I_0$
3. $4I_0, I_0$
4. $9I_0, I_0$

Two light sources are said to be coherent when their:

In Young's double-slit experiment, the intensity of light at a point on the screen where the path difference is $\lambda$ is $K$, ($\lambda$ being the wavelength of light used). The intensity at a point where the path difference is $\frac{\lambda}{4}$ will be:
1. $K$
2. $\frac{K}{4}$
3. $\frac{K}{2}$
4. zero