Ray Optics and Optical Instruments — Physics STD 12 Science — Question

Three electric bulbs of rating 60W each are joined in series and then connected to electric mains. The power consumed by these three bulbs will be

(a) 180 W

(b) 60 W

(c) 20 W

(d)

An element has number of electrons  = 2. Then what will be its atomic number?.

A point source of light B is placed at a distance L in front of the centre of a mirror of width d hung vertically on a wall. A man walks in front of the mirror along a line parallel to the mirror at a distance 2L from it as shown. The greatest distance over which he can see the image of the light source in the mirror is

(a) d/2

(b) d

(c) 2d

(d) 3d

What is the amount of work done to bring a charge of 4 × 10^-3C charge from infinity to a point whose electric potential is 2 × 10²V?

As the net electric flux through a closed surface is zero, the total charge contained in the closed surface is also:

Five equal resistances each of resistance R are connected as shown in the figure. A battery of V volts is connected between A and B. The current flowing in AFCEB will be

(a)

(b)

(c)

(d)

Range of wavelength of X-rays is:

Three waves are given below. I. Sound waves, II. Visible light waves, III. X-rays. Which of the above waves cannot be polarised?

If the magnetic dipole moment of an atom of diamagnetic material, paramagnetic material and ferromagnetic material denoted by  respectively then

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

Assertion    :  A potentiometer of longer length is used for accurate measurement.

Reason        : The potential gradient for a potentiometer of longer length with a given source of e.m.f. becomes small.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.