Atoms — Physics STD 12 Science — Question

Pick out the material that cannot be used to make permanent magnets.

During mean life of a radioactive element, the fraction that disintegrates is

(a) e

(b)

(c)

(d)

Scale used in moving coil galvanometer is:

In the adjoining circuit, the battery  has an e.m.f of 12 volt and zero internal resistance while the battery E has an e.m.f  of 2 volt. If the galvanometer G reads zero, then the value of the resistance X in ohm is

(a) 10

(b) 100

(c) 500

(d) 200

A semiconductor X is made by doping a germanium crystal with arsenic (Z = 33). A second semiconductor Y is made by doping germanium with indium (Z = 49). The two are joined end to end and connected to a battery as shown. Which of the following statements is correct

(a) X is P-type, Y is N-type and the junction is forward biased

(b) X is N-type, Y is P-type and the junction is forward biased

(c) X is P-type, Y is N-type and the junction is reverse biased

(d) X is N-type, Y is P-type and the junction is reverse biased

A circular loop carrying a current is replaced by an equivalent magnetic dipole. A point on the axis of the loop is

(a) An end-on position	(b) A broad side-on position
(c) Both (a) and (b)	(d) Neither (a) nor (b)

A simple pendulum with bob of mass m and conducting wire of length L swings under gravity through an angle 2θ. The earth’s magnetic field component in the direction perpendicular to swing is B. Maximum potential difference induced across the pendulum is

(a) 2BL sin	(b) BL sin
(c) BL sin	(d) 2BL sin

A polariser is used to

(a) Reduce intensity of light	(b) Produce polarised light
(c) Increase intensity of light	(d) Produce unpolarised light

A P-type semiconductor has acceptor levels 57 meV above the valence band. The maximum wavelength of light required to create a hole is (Planck’s constant h = 6.6  J-s)

(a) 57

(b) 57

(c) 217100

(d) 11.61