Wave Optics — Physics STD 12 Science — Question

Two point charges +9e and +e are at 16 cm away from each other. Where should another charge q be placed between them so that the system remains in equilibrium

(a) 24 cm from +9e

(b) 12 cm from +9e

(c) 24 cm from +e

(d) 12 cm from +e

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

A charge  exerts some force on a second charge . If third charge  is brought  near, the force of  exerted on

(a) Decreases

(b) Increases

(c) Remains unchanged

(d) Increases if  is of the same sign as  and decreases if  is of opposite sign

The light rays having photons of energy 1.8 eV are falling on a metal surface having a work function 1.2 eV. What is the stopping potential to be applied to stop the emitting electrons

(a) 3 eV

(b) 1.2 eV

(c) 0.6 eV

(d) 1.4 eV

When a resistor of 11 W is connected in series with an electric cell, the current flowing in it is 0.5 A.  Instead, when a resistor of 5 W is connected to the same electric cell in series, the current increases by 0.4 A. The internal resistance of the cell is

(a)  1.5 W

(b) 2 W

(c)  2.5 W

(d) 3.5 W

The oscillating electric and magnetic vectors of an electromagnetic wave are oriented along

(a) The same direction but differ in phase by 90°

(b) The same direction and are in phase

(c) Mutually perpendicular directions and are in phase

(d) Mutually perpendicular directions and differ in phase by 90°

When two deuterium nuclei fuse together to form a tritium nuclei, we get a

(a) Neutron

(b) Deutron

(c) α - particle

(d) Proton

To an observer on the earth the stars appear to twinkle. This can be ascribed to

(a) The fact that stars do not emit light continuously

(b) Frequent absorption of star light by their own atmosphere

(c) Frequent absorption of star light by the earth's atmosphere

(d) The refractive index fluctuations in the earth's atmosphere

In Young's double slit experiment, the distance between the slits is 1 mm and that between slit and screen is 1 meter and 10th fringe is 5 mm away from the central bright fringe, then wavelength of light used will be

(a) 5000 Å

(b) 6000 Å

(c) 7000 Å

(d) 8000 Å

Permanent magnets are the substances having the property of: