Magnetism and Matter — Physics STD 12 Science — Question

A charged particle enters in a uniform magnetic field with a certain velocity. The power delivered to the particle by the magnetic field depends on:

Assertion : Radioactivity of  undecayed radioactive nuclei of half life of 50 days is equal to that of 1.2   number of undecayed nuclei of some other material with half life of 60 days  

Reason    : Radioactivity is proportional to half-life.

(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.

Magnetic needle can remain safe in:

A capacitor is used to store 24 watt hour of energy at 1200 volt. What should be the capacitance of the capacitor

(a) 120 mF

(b) 120 μF

(c) 24 μF

(d) 24 mF

To get three images of a single object, one should have two plane mirrors at an angle of

(a) 30°

(b) 60°

(c) 90°

(d) 150°

Magnetic field can be defined as the:

The ampere-sec stands for the unit of:

Twists of suspension fibre should be removed in vibration magnetometer so that

(a) Time period be less	(b) Time period be more
(c) Magnet may vibrate freely	(d) Cannot be said with certainty

Velocity of light in a medium is 1.5 .  Its refractive index will be

(a) 8

(b) 6

(c) 4

(d) 2

Two points A and B are situated at a distance x and 2x respectively from the nearer pole of a magnet 2cm long. The ratio of magnetic field at A and B is: