Ray Optics and Optical Instruments — Physics STD 12 Science — Question

Mention the two characteristic properties of the material suitable for making core of a transformer.

Light is incident normally on a small plane surface. If the surface is rotated by an angle of 30° about the incident light, does the illuminance of the surface increase, decrease or remain same? Does your answer change if the light did not fall normally on the surface? 

Which part of electromagnetic spectrum has largest penetrating power?

When a p-type impurity is doped in a semiconductor, a large number of holes are created. This does not make the semiconductor charged. But when holes diffluse from the p-side to the n-side in a p-n junction, the n-side gets positively charged. Explain.

Answer the following questions:
The earth may have even reversed the direction of its field several times during its history of 4 to 5 billion years. How can geologists know about the earth’s field in such distant past?

A sphere rolls on a horizontal surface. If there any point of the sphere which has a vertical velocity?

How does the conductivity of a semiconductor change with rise in temperature?

Two Polaroids are placed with their optic axis perpendicular to each other. One of them is rotated through 45°, what is the intensity of light emerging from the second Polaroid if I₀ is the intensity of unpolarised light?