Modern Physics Miscellaneous MCQ Questions & Answers in Modern Physics | Physics
Learn Modern Physics Miscellaneous MCQ questions & answers in Modern Physics are available for students perparing for IIT-JEE, NEET, Engineering and Medical Enternace exam.
41.
The $$rms$$ value of the electric field of the light coming from the Sun is $$720\,N/C.$$ The average total energy density of the electromagnetic wave is
A
$$4.58 \times {10^{ - 6}}J/{m^3}$$
B
$$6.37 \times {10^{ - 9}}J/{m^3}$$
C
$$81.35 \times {10^{ - 12}}J/{m^3}$$
D
$$3.3 \times {10^{ - 3}}J/{m^3}$$
Answer :
$$4.58 \times {10^{ - 6}}J/{m^3}$$
$${E_{rms}} = 720$$
The average total energy density
$$\eqalign{
& \frac{1}{2}{ \in _0}E_0^2 = \frac{1}{2}{ \in _0}{\left[ {\sqrt 2 {E_{rms}}} \right]^2} = { \in _0}E_{rms}^2 \cr
& = 8.85 \times {10^{ - 12}} \times {\left( {720} \right)^2} = 4.58 \times {10^{ - 6}}J/{m^3} \cr} $$
42.
According to Einstein’s photoelectric equation, the plot of the kinetic energy of the emitted photo electrons from a metal Vs the frequency, of the incident radiation gives as straight the whose slope
A
depends both on the intensity of the radiation and the metal used
B
depends on the intensity of the radiation
C
depends on the nature of the metal used
D
is the same for the all metals and independent of the intensity of the radiation
Answer :
is the same for the all metals and independent of the intensity of the radiation
From Equation $$K.E = h\nu - \phi $$
slope of graph of $$K.E.$$ & $$\nu $$ is $$h$$ (Plank's constant) which is same for all metals