Physics Ncert Solutions Class 12th

An electromagnetic wave travelling along z-axis is given as E=E₀cos(kz-wt).choose the correct options from the following

(a) Tha associated magnetic field is given as B=1/ck $*$ E=1/w(k $*\mathit{E}$ )

(b) The electromagnetic field can be written in terms of associated magnetic field as E=c(b $*\mathit{k}$ )

(c) E=0,k.B=0

(d) K $*$ E=0,k $*\mathit{B}=0$

An electron is moving with an initial velocity v = v₀i and is in a magnetic field B = B₀ Then, its de-Broglie wavelength
(a) Remains constant
(b) Increases with time
(c) Decreases with time
(d) Increases and decreases periodically

An electromagnetic wave travels in vacuum along z-direction E=  (E₁iE₂j)cos(kz-wt). Choose the correct options from the following

(a) The associated magnetic field is given as B= (E₁i-E₂j)cos(kz-wt)

(b) The associated magnetic field is given as B= (E₁i-E₂j)cos(kz-wt)

(c) The given electro magnetic field is circularly polarised

(d) The given electromagnetic wave is plane polarised

An EM wave radiates outwards from a dipole antenna, with E₀as the amplitude of its electric field vector. The electric field E₀ which transports significant energy from the source falls off as

(a) 1/r³  

(b) 1/r²  

(c) 1/r  

(d) Remains constant

The ratio of contributions made by the electric field and magnetic field components to the intensity of an EM wave is

(a) C:1       

(b) c²:1         

(c) 1:1       

(d) :1

If E and B represent electric and magnetic field vectors of the electromagnetic wave, the direction of propagation of electromagnetic wave is along

(a) E     

(b) B   

(c)  B*E   

(d)  E*B

The electric field intensity produced by the radiations coming from a 100 W bulb at a 3 m distance is E. The electric field intensity produced by the radiations coming from 50 W bulb at the same distance is

(a) E/2           

(b) 2E         

(c) E/√2         

(d) E

Light with an energy flux of 20 W/cm² falls on a non-reflecting surface at normal incidence. If the surface has an area of 30 cm², the total momentum delivered (for complete absorption) during 30 min is

(a) 36 x 10^-5 kg-m/s               

(b) 36 x 10^-4 kg-m/s

(c) 108 x 10⁴ kg-m/s               

(d) 1.08 x 10⁷ kg-m/s

A linearly polarised electromagnetic wave given as E= E₀icos(kz-wt) is incident normally on a perfectly reflecting infinite wall at z=a. assuming that the material of the wall is optically inactive, the reflected wave will be given as

(a) E_r=E_oi(kz-wt)   

(b)  E_r =E_oicos(kz+wt       

(c) E_r = -E_oicos(kz+wt)       

(d) E_r = E_oisin(kz-wt)

One requires 11 eV of energy to dissociate a carbon monoxide molecule into carbon and oxygen atoms. The minimum frequency of the appropriate electromagnetic radiation to achieve the dissociation lies in

(a) Visible region               

(b) Infrared region

(c) Ultraviolet region           

(d) Microwave region