Atoms — Physics STD 12 Science — Question

Calculate the de-Brogile wavelength of an electron travelling at 1% of the speed of light:

Two equally charged, identical metal spheres A and B repel each other with a force 'F'. The spheres are kept fixed with a distance 'r' between them. A third identical, but uncharged sphere C is brought in contact with A and then placed at the mid-point of the line joining A and B. The magnitude of the net electric force on C is

(a) F

(b) 3F/4

(c) F/2

(d) F/4

In helium nucleus, there are

(a) 2 protons and 2 electrons	(b) 2 neutrons, 2 protons and 2 electrons
(c) 2 protons and 2 neutrons	(d) 2 positrons and 2 protons

A part of a long wire carrying a current i is bent into a circle of radius r as shown in figure. The net magnetic field at the centre O of the circular loop is

(a)

(b)

(c)

(d)

Drift velocity  varies with the intensity of electric field as per the relation

(a)

(b)

(c)  constant

(d)

A power transformer is used to step up an alternating e.m.f. of 220 V to 11 kV to transmit 4.4 kW of power. If the primary coil has 1000 turns, what is the current rating of the secondary ? Assume 100% efficiency for the transformer

(a) 4 A

(b) 0.4 A

(c) 0.04 A

(d) 0.2 A

At neutral temperature, the thermoelectric power   has the value

(a) Zero	(b) Maximum but negative
(c) Maximum but positive	(d) Minimum but positive

The magnetic field of the earth can be modelled by that of a point dipole placed at the centre of the earth. The dipole axis makes an angle of 11.3° with the axis of the earth. At Mumbai, declination is nearly zero. Then,

Two opposite charged particles oscillate about their mean equilibrium position in free space, with a frequency of 10⁹Hz. The wavelength of the corresponding electromagnetic wave produced is ______: