Dual Nature of Radiation and Matter — Physics STD 12 Science — Question

What happens to the wavelength of a photon after it collides with an electron?

Which of the following statements are true regarding radioactivity

(I)  All radioactive elements decay exponentially with time

(II)  Half life time of a radioactive element is time required for one half of the radioactive atoms to disintegrate

(III)  Age of earth can be determined with the help of radioactive dating

(IV)  Half life time of a radioactive element is 50% of its average life period

Select correct answer using the codes given below

Codes :

(a) I and II

(b) I, III and IV

(c) I, II and III

(d) II and III

An electron is moving along the positive X-axis. You want to apply a magnetic field for a short time so that the electron may reverse its direction and move parallel to the negative X-axis. This can be done by applying the magnetic field along

(a) Y-axis

(b) X-axis

(c) Y-axis only

(d) None of these

An electric bulb is rated 220 volt and 100 watt. Power consumed by it when operated on 110 volt is

(a) 50 watt

(b) 75 watt

(c) 90 watt

(d) 25 watt

The energy band gap of Si  is

(a) 0.70 eV	(b) 1.1 eV
(c) Between 0.70 eV  to 1.1 eV	(d) 5 eV

64 small drops of mercury, each of radius r and charge q coalesce to form a big drop. The ratio of the surface density of charge of each small drop with that of the big drop is

(a) 1 : 64

(b) 64 : 1

(c) 4 : 1

(d) 1 : 4

In the figure shown, the capacity of the condenser C is 2μF. The current in 2Ω  resistor is

(a) 9 A

(b) 0.9 A

(c)

(d)

A parallel plate capacitor is connected to a battery. The plates are pulled apart with a uniform speed. If x is the separation between the plates, the time rate of change of electrostatic energy of capacitor is proportional to

(a) x–2

(b) x

(c) x–1

(d) x2

Two independent parallel wires in which the current is flowing in the same direction. They will: