Troposphere: 1. The lowest layer of the atmosphere (0–12 km). 2. Contains most of the Earth’s weather phenomena. 3. Temperature decreases with altitude.
Thermosphere: 1. Extends from approximately 80 km to 500 km above the surface. 2. Contains ionized particles and reflects radio waves. 3. Temperature increases with altitude due to solar radiation.

Draw the pattern of the magnetic field lines for the two parallel straight conductors carrying current of same magnitude 'I' in opposite directions as shown. Show the direction of magnetic field at a point O which is equidistant from the two conductors. (Consider that the conductors are inserted normal to the plane of a rectangular cardboard.)