Alternating Current — Physics STD 12 Science — Question

In the following reaction the value of ‘X’ is

(a)

(b)

(c)

(d)

In the propagation of electromagnetic waves the angle between the direction of propagation and plane of polarisation is

(a) 0o

(b) 45o

(c) 90o

(d) 180o

For the ground state, the electron in the H-atom has an angular momentum = h, according to the simple Bohr model. Angular momentum is a vector and hence there will be infinitely many orbits with the vector pointing in all possible directions. In actuality, this is not true,

Which one of the following is more monocromatic?

A wire has resistance 12 Ω. It is bent in the form of a circle. The effective resistance between the two points on any diameter is equal to

(a) 12 Ω

(b) 6 Ω

(c) 3 Ω

(d) 24 Ω

A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence, the rod gains gravitational potential energy. The work required to do this comes from:

A hydrogen atom in its ground state absorbs 10.2 eV of energy. The orbital angular momentum is increased by

(a) 1.05   J-sec

(b) 3.16   J-sec

(c) 2.11   J-sec

(d) 4.22   J-sec

The half life period of a radioactive substance is 5 min. The amount of substance decayed in 20 min will be

(a) 93.75%

(b) 75%

(c) 25%

(d) 6.25%

A small bar magnet A oscillates in a horizontal plane with a period T at a place where the angle of dip is 60^o. When the same needle is made to oscillate in a vertical plane coinciding with the magnetic meridian, its period will be

(a)

(b) T

(c)

(d) 2T