Electromagnetic Waves — Physics STD 12 Science — Question

The mass number of a nucleus is

(a) Always less than its atomic number

(b) Always more than its atomic number

(c) Always equal to its atomic number

(d) Sometimes more than and sometimes equal to its atomic number

If the amplitude ratio of two sources producing interference is 3 : 5, the ratio of intensities at maxima and minima is

(a) 25 : 16

(b) 5 : 3

(c) 16 : 1

(d) 25 : 9

A capacitor 4 μF charged to 50  V is connected to another capacitor of 2 μF  charged to 100 V with plates of like charges connected together. The total energy before and after connection in multiples of  (  is

(a) 1.5 and 1.33

(b) 1.33 and 1.5

(c) 3.0 and 2.67

(d) 2.67 and 3.0

A convex mirror has a focal length f. A real object is placed at a distance f in front of it from the pole produces an image at

(a) Infinity

(b) f

(c) f/2

(d) 2f

X-rays are

(a) Stream of electrons

(b) Stream of positively charged particles

(c) Electromagnetic radiations of high frequency

(d) Stream of uncharged particles

An object is immersed in a fluid. In order that the object becomes invisible, it should

(a) Behave as a perfect reflector

(b) Absorb all light falling on it

(c) Have refractive index one

(d) Have refractive index exactly matching with that of the surrounding fluid

Two waves of same amplitude and same wavelength are superimposed in different phases. The amplitude of the resultant wave will be maximum when the phase difference between them is:

Eight dipoles of charges of magnitude e are placed inside a cube. The total electric flux coming out of the cube will be

(a)

(b)

(c)

(d) Zero

Light is a form of _______ that we can detect with our ________ .

Assertion :  Basic difference between an electric line and magnetic line of force is that former is discontinuous and the latter is continuous or endless.

Reason     : No electric lines of forces exist inside a charged body but magnetic lines do exist inside a magnet.

(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.