A cast steel frame is to be used as the core of an inductor. An 800 turn coil is wound on the centre limb of the frame which has two similar outer limbs in parallel with each other. The frame has the following parameters: Outer limb: c. s.a. of 2000 mm2 and length of 700mm. Centre limb: c. s.a of 4000 mm2 and length of 250 mm. Determine the coil current to set up a flux of 1 mwb if a saw-tooth (an air-gap) of 1 mm is cut in the centre limb. The relative permeability of steel is 1000.

Consider a large isothermal enclosure that is maintained at a uniform temperature of 2000 k. calculate the emissive power of the radiation that emerges from a small aperture on the enclosure surface. what is the wavelength ? , below which 10% of the emission is concentrated? what is the wavelength ? 2 above which 10% of the emission is concentrated? determine the wavelength at which maximum spectral emissive power occurs. what is the irradiation incident on a small object placed inside the enclosure?