wiz-icon
MyQuestionIcon
MyQuestionIcon
1
You visited us 1 times! Enjoying our articles? Unlock Full Access!
Question

Three charges +4q, Q and q are placed in a straight line of length l at points at distances 0, l/2, and l respectively. What should be Q in order to make the net force on q to be zero?

A
-q
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
B
-2q
No worries! We‘ve got your back. Try BYJU‘S free classes today!
C
q2
No worries! We‘ve got your back. Try BYJU‘S free classes today!
D
4q
No worries! We‘ve got your back. Try BYJU‘S free classes today!
Open in App
Solution

The correct option is A -q
Step 1: Force on q due to all other charges [Ref Fig 1]
Considering the charge Q to be positive in the beginning, mention the direction of forces in the figure.
Applying Coulomb's law, the force exerted on the charge q due to Q :
F1=KqQ(l/2)2=4KqQl2 ....(1).

The force exerted on the charge q due to 4q :
F2=Kq 4ql2=4Kq2l2 ....(2).

Step 2 : Net force on q
Net force =F1+F2=0

Using equations (1) and (2)

4KqQl2+4Kq2l2=0

So, qQ+q2=0

q(Q+q)=0

Since q cannot be 0
Q+q=0
Q=q
Hence, Q should be -q in order to make the net force on q to be zero.

Note -Now we know the nature of Q we can show the actual direction of the forces and see that forces are in opposite directions making the net force on q zero.[Ref Fig 2]

Hence, Option A is correct

2102255_332365_ans_fe8586f53e10410d9ef904b8b08227dc.png

flag
Suggest Corrections
thumbs-up
1
Join BYJU'S Learning Program
similar_icon
Related Videos
thumbnail
lock
Visualising Electric Fields - Electric Field Lines
PHYSICS
Watch in App
Join BYJU'S Learning Program
CrossIcon