Science (English Medium) इयत्ता १२ - CBSE Important Questions

In what way is Gauss's law in magnetism different from that used in electrostatics ? Explain briefly.

The Earth's magnetic field at the Equator is approximately 0.4 G. Estimate the Earth's magnetic dipole moment. Given : Radius of the Earth = 6400 km.

State Lenz's law. Illustrate, by giving an example, how this law helps in predicting the direction of the current in a loop in the presence of a changing magnetic flux.

In a given coil of self-inductance of 5 mH, current changes from 4 A to 1 A in 30 ms. Calculate the emf induced in the coil.

State any two causes of energy loss in actual transformers.

Derive the expression for the self-inductance of a long solenoid of cross sectional area A and length l, having n turns per unit length.

Draw a graph to show variation of capacitive-reactance with frequency in an a.c. circuit.

How are infrared waves produced?

How are X-rays produced?

Give any two uses of infrared waves.

A ray of light passes through an equilateral glass prism such that the angle of incidence is equal to the angle of emergence and each of these angles is equal to 3/4 of angle of prism. Find the angle of deviation.

Use Huygens' principle to show the propagation of a plane wavefront from a denser medium to a rarer medium. Hence find the ratio of the speeds of wavefronts in the two media.

Use the mirror equation to show that an object placed between f and 2f of a concave mirror produces a real image beyond 2f.

Use the mirror equation to show that a convex mirror always produces a virtual image independent of the location of the object.

Write the necessary conditions to obtain sustained interference fringes.

In Young's double slit experiment, plot a graph showing the variation of fringe width versus the distance of the screen from the plane of the slits keeping other parameters same. What information can one obtain from the slope of the curve?

What is the effect on the fringe width if the distance between the slits is reduced keeping other parameters same?

Derive the expression of Brewster's law when unpolarised light passing from a rarer to a denser medium gets polarised on reflection at the inteface.

In a double-slit experiment using the light of wavelength 600 nm, the angular width of the fringe formed on a distant screen is 0.1°. Find the spacing between the two slits.

Show that the angular width of the first diffraction fringe is half that of the central fringe.