Atoms — Physics STD 12 Science — Question

Assertion  : In high latitude one sees colourful curtains of light hanging down from high altitudes.
Reason      :  The high energy charged particles from the sun are deflected to polar regions by the magnetic field of the earth.(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.(c) If assertion is true but reason is false.(d) If the assertion and reason both are false.

A point source of light is placed at a distance, of 2f from a converging lens of focal length f. The intensity on the other side of the lens is maximum at a distance:

From which layer of atmosphere are radiowaves reflected ?

Two thin lenses, one of focal length + 60 cm and the other of focal length – 20 cm are put in contact. The combined focal length is(a) + 15 cm(b) – 15 cm(c) + 30 cm(d) –30 cm

In insulator:

A nuclear bomb exploded 200 km above the surface of moon. The sound of explosion on the moon(a) Will heard before the explosion is seen(b) Will be heard at the same time(c) Will be heard after explosion(d) Will not heard at all

If a lens is cut into two pieces perpendicular to the principal axis and only one part is used, the intensity of the image

Which of the following systems may be adequately described by classical physics?

The impurity atoms with which pure silicon may be doped to make it a p-type semiconductor are those of:

1. Phosphorus.
2. Boron.
3. Antimony.
4. Aluminium.

When the electron in a H-atom jumps from 6th excited state to 2nd excited state, the maximum number of emission lines will be.