Atoms — Physics STD 12 Science — Question

Assertion :   The properties of paramagnetic and ferromagnetic substance are not effected by heating.

Reason     : As temperature rises, the alignment of molecular magnets gradually decreases.

(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 assertion is false but reason is true.

What is the use of a Van de Graff generator?

Why is the screen of the cathode ray tube coated ? Name the material used for coating:

In Young’s double slit experiment, distance between two sources is 0.1 mm. The distance of screen from the sources is 20 cm. Wavelength of light used is 5460 Å. Then angular position of the first dark fringe is

(a) 0.08°

(b) 0.16°

(c) 0.20°

(d) 0.313°

A freshly prepared radioactive source of half-life 2h emits radiation of intensity which is 64 times the permissible safe level. The minimum time after which it would be possible to work safely with this source is:

Time period in vibration magnetometer will be infinity at

(a) Magnetic equator

(b) Magnetic poles

(c) Equator

(d) At all places

A resistance R is to be measured using a meter bridge. Student chooses the standard resistance S to be 100Ω. He finds the null point at l₁ = 2.9cm. He is told to attempt to improve the accuracy. Which of the following is a useful way?

In the Bohr model of the hydrogen atom, let R, v and E represent the radius of the orbit, the speed of electron and the total energy of the electron respectively. Which of the following quantity is proportional to the quantum number n

(a) R/E

(b) E/v

(c) RE

(d) vR

Characteristic X-rays are produced due to

(a) Transfer of momentum in collision of electrons with target atoms

(b) Transition of electrons from higher to lower electronic orbits in an atom

(c) Heating of the target

(d) Transfer of energy in collision of electrons with atoms in the target