Gujarati
Hindi
2. Electric Potential and Capacitance
normal

The distance between the plates of a charged parallel plate capacitor is $5\  cm$ and electric field inside the plates is $200\  Vcm^{-1}$. An uncharged metal bar of width $2\  cm$ is fully immersed into the capacitor. The length of the metal bar is same as that of plate of capacitor. The voltage across capacitor after the immersion of the bar is......$V$

A

$0$

B

$400$

C

$600$

D

$100$

Solution

When the uncharged metal bar of width of $2 \mathrm{cm}$ is immersed into the capacitor, the distance between the plates of capacitor reduces and becomes: $(5-2) c m=3 c m$

since, the electric field$:$ $E=\frac{V}{d},$ where $E=200 \mathrm{V} / \mathrm{cm}, d=3 \mathrm{cm}$

so potential$:$ $V=E \times d=200 \times 3=600 V$

Standard 12
Physics

Similar Questions

Answer the following:

$(a)$ The top of the atmosphere is at about $400\; kV$ with respect to the surface of the earth, corresponding to an electric field that decreases with altitude. Near the surface of the earth, the field is about $100\; Vm ^{-1} .$ Why then do we not get an electric shock as we step out of our house into the open? (Assume the house to be a steel cage so there is no field inside!)

$(b)$ A man fixes outside his house one evening a two metre high insulating slab carrying on its top a large aluminium sheet of area $1\; m ^{2} .$ Will he get an electric shock if he touches the metal sheet next morning?

$(c)$ The discharging current in the atmosphere due to the small conductivity of air is known to be $1800 \;A$ on an average over the globe. Why then does the atmosphere not discharge itself completely in due course and become electrically neutral? In other words, what keeps the atmosphere charged?

$(d)$ What are the forms of energy into which the electrical energy of the atmosphere is dissipated during a lightning? (The earth has an electric field of about $100\; Vm ^{-1}$ at its surface in the downward direction, corresponding to a surface charge density $=-10^{-9} \;C \,m ^{-2} .$ Due to the slight conductivity of the atmosphere up to about $50\; km$ (beyond which it is good conductor), about $+1800 \;C$ is pumped every second into the earth as a whole. The earth, however, does not get discharged since thunderstorms and lightning occurring continually all over the globe pump an equal amount of negative charge on the earth.)

medium

Start a Free Trial Now

Confusing about what to choose? Our team will schedule a demo shortly.