The intensity of each of the two slits in Young's double slit experiment is \(I_0\). What is the minimum separation between the points on the screen, where intensities are \(2I_0\) and \(I_0\), if fringe width is \(b\)?
1. \(b \over 5 \)
2. \(b \over 8 \)
3. \(b \over 12 \)
4. \(b \over 4\)
A metal rod at a temperature of \(145^\circ\mathrm{C}\), radiates energy at a rate of \(17~\mathrm{W}\). If its temperature is increased to \(273^\circ\mathrm{C}\), then it will radiate at the rate of:
1. \(
49.6 \mathrm{~W}
\)
2. \( 17.5 \mathrm{~W}
\)
3. \( 50.3 \mathrm{~W}
\)
4. \(67.5 \mathrm{~W}\)
A square wire of side \(2.0~\mathrm{cm}\) is placed \(20~\mathrm{cm}\) in front of a concave mirror of focal length \(10~\mathrm{cm}\) with its centre on the axis of the mirror and its plane normal to the axis. The area enclosed by the image of wire is:
1. \(
7.5 \mathrm{~cm}^2
\)
2. \( 6 \mathrm{~cm}^2
\)
3. \(2 \mathrm{~cm}^2 \)
4. \(
4 \mathrm{~cm}^2\)