Two light sources are said to be coherent when their:

1.	Amplitudes are equal and have a constant phase difference
2.	Wavelengths are equal.
3.	Intensities are equal.
4.	Frequencies are equal and have a constant phase difference.

Which statement is true for interference?

In Young's double-slit experiment sources of equal intensities are used. The distance between the slits is \(d\) and the wavelength of light used is \(\lambda (\lambda<<d)\). The angular separation of nearest points on either side of central maximum where intensities become half of the maximum value is:
1. \(\frac{\lambda}{d}\)
2. \(\frac{\lambda}{2d}\)
3. \(\frac{\lambda}{4d}\)
4. \(\frac{\lambda}{6d}\)

Four coherent sources of intensity \(I\) are superimposed constructively at a point. The intensity at that point is:
1. \(4I\)
2. \(8I\)
3. \(16I\)
4. \(24I\)

Two waves, each of intensity ${}_{}$\(i_{0}\) and wavelength \(0.2\) m, start from sources \(A\) and \(B\) and meet at point \(P\) as shown in the figure. If \(AP=0.5\) m, \(BP=0.8\) m, then intensity at \(P\) is:

If the \(5\)th order maxima of wavelength \(4000~\mathring{A}\) in Young's double-slit experiment coincides with the \(n\)th order maxima of wavelength \(5000~\mathring{A},\) then \(n\) is equal to:
1. \(5\)
2. \(8\)
3. \(4\)
4. \(10\)

Young's double-slit experiment is performed in a liquid. The \(10\)^th bright fringe in the liquid lies where the \(8\)th dark fringe lies in a vacuum. The refractive index of the liquid is approximately:
1. \(1.81\)
2. \(1.67\)
3. \(1.54\)
4. \(1.33\)

If the ratio of amplitudes of two coherent sources producing an interference pattern is \(3:4\), the ratio of intensities at maxima and minima is:
1. \(3:4\)
2. \(9:16\)
3. \(49:1\)
4. \(25:7\)

Two coherent sources are \(0.3~\text{mm}\) apart. They are \(1~\text{m}\) away from the screen. The second dark fringe is at a distance of \(0.3~\text{cm}\)  from the center. The distance of the fourth bright fringe from the centre is:
1. \(0.6~\text{cm}\)
2. \(0.8~\text{cm}\)
3. \(1.2~\text{cm}\)
4. \(0.12~\text{cm}\)