A molecule of a substance has permanent dipole moment $p$. A mole of this substance is polarised by applying a strong electrostatic field $E$. The direction of the field is suddenly changed by an angle of $60^{\circ} .$ If $N$ is the Avogadro's number the amount of work done by the field is
A$\frac{1}{2}NpE$
B$NpE$
C$\;\frac{3}{2}NpE$
D$2NpE$
NEET 2017, Medium
Download our app for free and get started
A$\frac{1}{2}NpE$
a $(\vec{U})=-\vec{p} \cdot \vec{E}=-p E \cos \theta$
$W=\Delta U$
$W=-N p E\left(\cos 60^{\circ}-\cos 0^{\circ}\right)=\frac{1}{2} N p E$
Download our app
and get started for free
Experience the future of education. Simply download our apps or reach out to us for more information. Let's shape the future of learning together!No signup needed.*
The capacity of a parallel plate condenser is $10\,\mu \,F$, when the distance between its plates is $8 \,cm$. If the distance between the plates is reduced to $4\, cm$, then the capacity of this parallel plate condenser will be.........$\mu \,F$
$1000$ small water drops each of radius $r$ and charge $q$ coalesce together to form one spherical drop. The potential of the big drop is larger than that of the smaller drop by a factor of
A capacitor $C_1$ is charged up to a voltage $V\, = 60\,V$ by connecting it to battery $B$ through switch $( 1)$, Now $C_1$ is disconnected from battery and connected to a circuit consisting of two uncharged capacitors $C_2\, = 3.0\,\mu F$ and $C_3\,= 6.0\,\mu F$ through a switch $(2)$ as shown in the figure. The sum of final charges on $C_2$ and $C_3$ is......$\mu C$
A conducting sphere of radius $10\, cm$ is charged $10\,\mu \,C$. Another uncharged sphere of radius $20\, cm$ is allowed to touch it for some time. After that if the sphere are separated, then surface density of charges, on the spheres will be in the ratio of
The potential at a point $x$ (measured in $μ\ m$) due to some charges situated on the $ x$-axis is given by $V(x)$ =$\frac{{20}}{{{x^2} - 4}}$ $volt$ The electric field $E$ at $x = 4\ μ m$ is given by
In the $R-C$ circuit shown in the figure the total energy of $3.6 \times 10^{-3}\ J$ is dissipated in the $10$ $\Omega$ resistor when the switch $S$ is closed. The initial charge on the capacitor is.....$\mu C$
If a battery of voltage $V$ is connected across terminals $I$ of the block box shown in figure, an ideal voltmeter connected to terminals $II$ gives a reading of $V/2$, while if the battery is connected to terminals $II$, a voltmeter across terminals $I$ reads $V$. The black box may contain
The electrostatic potential inside a charged spherical ball is given by $\phi= a{r^2} + b$ where $r$ is the distance from the centre and $a, b$ are constants. Then the charge density inside the ball is: