Electric Charges and Fields — Physics STD 12 Science — Question

For parallel capacitor having plates with finite area, the electric field lines bend outward at the edges. This effect is called ___________ .

Find out the value of current through 2Ω resistance for the given circuit

(a) 5 A

(b) 2 A

(c) Zero

(d) 4 A

Two coherent sources of different intensities send waves which interfere. The ratio of maximum intensity to the minimum intensity is 25. The intensities of the sources are in the ratio

(a) 25 : 1

(b) 5 : 1

(c) 9 : 4

(d) 25 : 16

In an electron gun the control grid is given a negative potential relative to cathode in order to

(a) Decelerate electrons

(b) Repel electrons and thus to control the number of electrons passing through it

(c) To select electrons of same velocity and to converge them along the axis

(d) To decrease the kinetic energy of electrons

The optical density of turpentine is higher than that of water while its mass density is lower. Fig. shows a layer of turpentine floating over water in a container. For which one of the four rays incident on turpentine in Fig, the path shown is correct?

Two thin lenses of focal lengths f₁ and f₂ are in contact.  The focal length of this combination is

(a)

(b)

(c)

(d)

Unit of magnetic flux density (or magnetic induction) is

(a) Tesla	(b) Weber/metre2
(c) Newton/ampere-metre	(d) All of the above

Which one of the following devices makes use of the electrons to strike certain substances to produce fluorescence

(a) Thermionic valve	(b) Photoelectric cell
(c) Cathode ray oscilloscope	(d) Electron gun

Two sources of equal emf are connected to an external resistance R. The internal resistances of the two sources are  and  . If the potential difference across the source having internal resistance  is zero, then

(a)	(b)
(c)	(d)

Capacitance of a parallel plate capacitor becomes 4/3 times its original value if a dielectric slab of thickness t = d/2 is inserted between the plates (d is the separation between the plates). The dielectric constant of the slab is

(a) 8

(b) 4

(c) 6

(d) 2