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The distance between the two charges 25μC and 36μC is 11cm. At what point on the line joining the two, will the intensity be zero?
A. At a distance of 5cm from 25μC
B. At a distance of 5cm from 36μC
C. At a distance of 10cm from 25μC
D. At a distance of 11cm from 36μC

Answer
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Hint: To answer this question we will first define an electric field and give its formula. Later we will draw a diagram exactly as stated in the question. Next we will apply the formula for electric field for both charges and equate them with each other to find the answer.

Formula used:
E=kqr2
Where, q is the charge, k is a constant with 8.99×109Nm2C2 value and r is the distance between charges.

Complete step by step answer:
Let us see what electric field intensity is: The electric field is the area around an electric charge where its impact can be felt. The force experienced by a unit positive charge put at a spot is the electric field intensity at that point.Look at the diagram:
seo images

Let the charge at point A be 25μC and at B be 36μC. Let O be the point where intensity is zero. It is at a distance ‘x’ from point A, then it is obvious that it is at a distance ‘11-x’ from point B.Now we will apply the equation individually for charge at A and charge at B.For charge at point A:
EA=k25×106x2
Let this be equation 1
EA=k25×106x2.......(1)
Now we will find at point B:
EB=k36×106(11x)2
Let this be equation 2
EB=k36×106(11x)2.......(2)

Now let us equate equations 1 and 2, we get:
EA=EB
k25×106x2=k36×106(11x)2
25x2=36(11x)2
(11x)2x2=3625
(11x)x=3625
Taking root on both sides
(11x)x=65
(555x)=6x
55=6x+5x
55=11x
x=5511
x=5cm
Hence the correct answer is that the intensity will be zero at a distance of 5cmfrom 25μC.

Hence the correct answer is option A.

Note: Students make a mistake while selecting a point where intensity is zero. In this question, to the left side of point A or right side of point B the intensity cannot be zero because at both these points intensities will add up as both are positive charges. Hence it will be zero only in between them.