Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Electrostatics question

2004 · Shift 0 · Q130
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Main
  3. /Physics
  4. /Electrostatics
  5. /2004 · Shift 0 · Q130

Electrostatics question

2004 · Shift 0 · Q130

JEE MainPhysicsElectrostaticsMCQ+4 / −1
A charged oil drop is suspended in a uniform field of 3×104v/m3 \times {10^4}v/m3×104v/m so that it neither falls nor rises. The charge on the drop will be (Take the mass of the charge =9.9×10−15  kg= 9.9 \times {10^{ - 15}}\,\,kg=9.9×10−15kg and g=10 m/s2g = 10\,m/{s^2}g=10m/s2)
  1. A
    1.6×10−18 C1.6 \times {10^{ - 18}}\,C1.6×10−18C
  2. B
    3.2×10−18 C3.2 \times {10^{ - 18}}\,C3.2×10−18C
  3. C
    3.3×10−18 C3.3 \times {10^{ - 18}}\,C3.3×10−18C
  4. D
    4.8×10−18 C4.8 \times {10^{ - 18}}\,C4.8×10−18C
View written solutionFree

Correct answer: C

  1. Condition for suspension

Since the oil drop neither rises nor falls, the net force on it is zero.

So, electric force balances weight:

qE=mgqE = mgqE=mg

Hence,

q=mgEq = \frac{mg}{E}q=Emg​

  1. Substitute given values

Given:

m=9.9×10−15 kgm = 9.9 \times 10^{-15}\,\text{kg}m=9.9×10−15kg g=10 m/s2g = 10\,\text{m/s}^2g=10m/s2 E=3×104 V/mE = 3 \times 10^4\,\text{V/m}E=3×104V/m

Therefore,

q=(9.9×10−15)(10)3×104q = \frac{(9.9 \times 10^{-15})(10)}{3 \times 10^4}q=3×104(9.9×10−15)(10)​

  1. Simplify

q=9.9×10−143×104q = \frac{9.9 \times 10^{-14}}{3 \times 10^4}q=3×1049.9×10−14​

q=3.3×10−18 Cq = 3.3 \times 10^{-18}\,\text{C}q=3.3×10−18C

  1. Match with options

The calculated charge is:

3.3×10−18 C\boxed{3.3 \times 10^{-18}\,\text{C}}3.3×10−18C​

So the correct option is C.

PreviousNext

More from Electrostatics

  • Two spherical conductors B and C having equal radii and carrying equal charges on them repel each other with a force F when kept apart at some distance. A third spherical conductor having same radius as that B but uncharged is…2004 · MCQ
  • A charge particle ′q′ is shot towards another charged particle ′Q′ which is fixed, with a speed ′v′. It approaches ′Q′ upto a closest distance r and then returns. If q were given a speed of ′2v′ the closest distances of…2004 · MCQ
  • Three charges −q1​,+q2​ and −q3​ are placed as shown in the figure. The x-component of the force on −q1​ is proportional to Includes diagram2003 · MCQ
  • If the electric flux entering and leaving an enclosed surface respectively is ϕ1​ and ϕ2​, the electric charge inside the surface will be2003 · MCQ
  • A thin spherical conducting shell of radius R has a charge q. Another charge Q is placed at the center of the shell. The electrostatic potential at a point P a distance 2R​ from the center of the shell is2003 · MCQ
  • On moving a charge of 20 coulomb by 2cm,2J of work is done, then the potential differences between the points is2002 · MCQ
  • A charged particle q is placed at the centre O of cube of length L(ABCDEFGH). Another same charge q is placed at a distance L from O. Then the electric flux through ABCD is Includes diagram2002 · MCQ
  • If a charge q is placed at the center of the line joining two equal charges Q such that the system is in equilibrium then the value of q is2002 · MCQ