A) 0.01 J/\[4\times {{10}^{-3}}V\]
B) 0.1 J/\[2\times {{10}^{-3}}V\]
C) 1.0 J/\[{{f}_{R}}<{{f}_{G}}<{{f}_{V}}\]
D) 10 J/\[{{f}_{V}}<{{f}_{G}}<{{f}_{R}}\]
Correct Answer: B
Solution :
Key Idea: Energy density in the energy per unit volume. The energy per unit volume or the energy density is given by \[\frac{{{h}_{1}}}{{{h}_{2}}}=\frac{u_{1}^{2}}{u_{2}^{2}}\] ??(i) where \[{{u}_{2}}=2{{u}_{1}},\,{{v}_{1}}=u\] is permittivity of free space and E is electric field. Also \[\text{=}\frac{\text{Total}\,\text{distance}}{\text{Velocity}}\] ??(ii) \[=100+1000=1100m\] From Eqs. (i) and (ii), we have \[=\frac{45\times 5}{18}=12.5m/s\] Given, \[\therefore \] \[t=\frac{1100}{12.5}=88s\] \[v=u-gt\] \[\therefore \] \[u=gt\] Note: We can also say that if electric field \[y=m+c\] exists in some space, then the space is a store of energy whose amount per unit volume is equal to energy density.
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