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Electric Field - Practice Questions & MCQ

Edited By admin | Updated on Sep 18, 2023 18:34 AM | #JEE Main

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  • Electric field is considered one of the most asked concept.

  • 71 Questions around this concept.

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If $E$ is the electric field intensity of an electrostatic field, then the electrostatic energy density is proportional  to  

If a charge  q is placed at the centre of the line joining two equal charges Q  such that the system is in equilibrium then the value of q is 

ABC is an equilateral triangle. Charges +q are placed at each corner. The electric intensity at O will be

Two point charges  +8q and  -2q are located at x = 0  and x = L respectively. The location of a point on the x axis at which the net electric field due to these two point charges is zero is

  The bob of a simple pendulum has a mass of 2 g and a charge of $5.0 \mu C$. It is at rest in a uniform horizontal electric field of intensity $2000 \mathrm{~V} / \mathrm{m}$. At equilibrium, the angle that the pendulum makes with the vertical is : (take $g=10 \mathrm{~m} / \mathrm{s}^2$ ).

What is the magnitude of a point charge due to which the electric field 30 cm away has the magnitude 2 Newton/coulomb [1/4\pi \varepsilon _{0}=9\times 10^{9}Nm^{2}] ?

Two point charges Q and – 3Q are placed at some distance apart. If the electric field at the location of Q is E, then at the locality of – 3Q, it is

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A long cylindrical shell carries positive surface charge $\sigma$ in the upper half and negative surface charge $-\sigma$ in the lower half. The electric field lines around the cylinder will look like figure given in : (figures are schematic and not drawn to scale)

The unit of intensity of electric field is:

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Charges are placed on the vertices of a square as shown. Let $\vec{E}$ be the electric field and V the potential at the centre. If the charges on A and B are interchanged with those on D and C respectively, then

Concepts Covered - 1

Electric field

Electric field and electric lines of force:

The space around a charge in which another charged particle experiences a force is said to have an electric field in it. 

Electric Field Intensity: 

The electric field intensity at any point is defined as the force experienced by a unit positive charge placed at that point.

                                                                     

Electric field intensity,

$
E=\frac{F}{q_0}
$

where F is the force experienced by q 0 . The Sl unit of E is,

$
\frac{\text { Newton }}{\text { Columb }}=\frac{\text { Volt }}{\text { meter }}=\frac{\text { Joule }}{\text { Coulomb } \times \text { Meter }}
$


The dimensional formula is $\left[M L T^{-3} A^{-1}\right]$

The electric field is a vector quantity and due to positive charge is away from the charge and for the negative charge, it is towards the charge.

Electric field due to a point charge: 

                                                                

Consider a point charge placed at the origin O. Let a test charge q0 is placed at P which is at a distance r from O. Force F on test charge q0 is

$
F=\frac{1}{4 \pi \epsilon_0} \frac{q q_0}{r^2} \hat{r}
$


The electric field at point $P$ due to $q$ is

$
E=\lim _{q_0 \rightarrow 0} \frac{F}{q_0}=\lim _{q_0 \rightarrow 0} \frac{1}{q_0} \frac{1}{4 \pi \epsilon_0} \frac{q q_0}{r^2} \hat{r}=\frac{1}{4 \pi \epsilon_0} \frac{q}{r^2} \hat{r}
$

(As $\mathrm{q}_0$ tends to zero the electric field produced by q is not affected by $\mathrm{q}_0$.)
The magnitude of the electric field

$
E=\frac{1}{4 \pi \epsilon_0} \frac{q}{r^2}
$
 

Electric field due to a system of charge:

Electric field obeys the superposition principle. That is the electric field due to a system of charge at a point is equal to the vector sum of all the electric fields. 

 

 

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Electric field

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