24 + Interview Questions in ELECTROSTATIC-FORCES IN GENERAL AWARENESS Page 1 InterviewSolution

1.	Eight identical point charges of q coulomb each are placed at the corners of a cube side 0.1m. Calculate electric field at the centre of the cube. Calculate the field at the center when one of the corner charges is removed.
Answer» Correct Answer - zero, `1.2 xx 10^(12)q NC^(-1)` towards the corner having no charge

Discussion

2.	How many electrons are there in one coulomb of negative charge?
Answer» Correct Answer - `6.25 xx 10^(18)"electron"`

Discussion

3.	A stream of electrons moving with a velocity of `3xx10^(7) ms^(-1)` is deflected by 2 mm in traversing a distance of 0.1 m in a uniform electric field of strength `18 Vm^(-1)` in Fig. 1.42. An electron enters the field symmetrically between the plates with a speed `upsilon_(0)`. The length of each plate is l. Find the angle of deviation of the bath of the electron as it comes out of the field.
Answer» Correct Answer - `2 xx 10^(11)C kg^(-1)`

Discussion

4.	Obtain the dimensional formula of `epsilon_(0)`.
Answer» Correct Answer - `M ^(-1) L^(-3)T^(4) I^(2)`

Discussion

5.	Calculate the coulomb force between two electrons separated by `0.8xx10^(-15) m`.
Answer» Correct Answer - 360 N

Discussion

6.	A simple pendulum consists of a small sphere of mass `m` suspended by a thread of length `l`. the sphere carries a positive charge `q`. The pendulum is placed in a uniform electric field of strength `E` directed vertically upwards. With what period will pendulum oscillate if the electrostatic force acting on the sphere is less than the gravitational force ?
Answer» Correct Answer - `(T=2pi sqrt((l)/(g-qE//m)))`

Discussion

7.	Two pith ball of mass 0.5 each are suspended from a common point O by means of silk threads, each of length 20 cm. When the balls are given equal and similar charges, they repel each other so that the two threads make an angle of `60^(@)` with each-other. Determine the charge on each ball.
Answer» Correct Answer - `1.12 xx 10 ^(-7)C`

Discussion

8.	Two small spheres each of mass m are suspended from a common point by threads 0.5 m long. They are equally charged and repel each other to a distance of 0.28m. If `=g10ms^(-2)`, what is the charge on each sphere?
Answer» Correct Answer - `1.594 xx 10 ^(-8)C`

Discussion

9.	If an oil drop of weight `3.2xx10^(-13) N` is balanced in an electric field of `5xx10^(5) Vm^(-1)`, find the charge on the oil drop.
Answer» Correct Answer - `0.64 xx 10 ^(-18)C`

Discussion

10.	Two particles (free to move) with charges `+q` and `+4q` are a distance L apart. A third charge is placed so that the entire system is in equilibrium. (a) Find the location, magnitude and sign of the third charge.(b) Show that the equilibrium is unstable.
Answer» Correct Answer - `" A negative charge of "(4e)/(9)" at a distance of " (2l)/(3)" from +4e chagre"`

Discussion

11.	Two pont chargees `q_(1) " and " q_(2) " of " 2xx10^(-8) C " and " -2xx10^(-8) C` respectively are placed 0.4 m apart. Calculate the electric field at the centre of the line joining the two charges.
Answer» Correct Answer - `900 NC^(1)`, towards the -ve change

Discussion

12.	Two charges, one `+5 mu C ` and another `-5 mu C` are placed 1 mm apart. Calculate the dipole moment.
Answer» Correct Answer - `5xx 10 ^(-9) cm`

Discussion

13.	Two point charges of `+2xx10^(-8) C` are placed 6 apart. Determine the force on a point charge of `+1xx10^(-8) C ` placed at a distance of 5 cm from each of the two given charges.
Answer» Correct Answer - `8.64 xx 10^(-4) N`

Discussion

14.	Determine the electric field produced by a helium nucleus at a distance of 1 Å from it.
Answer» Correct Answer - `2.88 xx 10^(11)NC^(-1)`

Discussion

15.	A proton falls dwon through a distance of 2 cm in a uniform electric field of magnitude `3.34xx10^(3) NC^(-1)`. Determine (i) the acceleration of the electron (ii) the time taken by the proton to fall through the distance of 2 cm, and (iii) the direction of the electric field.
Answer» Correct Answer - `3.2 xx 10^(11) ms^(-2), 3.54 xx 10^(-11)s^(-1),` vertically downwards

Discussion

16.	A positive charge of `20 mu C` is placed 2 m away from a negative charge of `20 mu C`. Determine the electric field at a point 2 m away from each charges.
Answer» Correct Answer - `4.5 xx 10^(4) NC^(-1)`

Discussion

17.	Calculate the charge on an alpha particle. Given on a proton`=1.6xx10^(19) C`.
Answer» Correct Answer - `+3.2 xx 10^(-19) C`

Discussion

18.	Calculate the charge on `._(26)F^(56)` nucleus. Given charge on a proton `=1.6xx10^(-19)` C.
Answer» Correct Answer - `+4.16 xx 10 ^(-18) C`

Discussion

19.	If `F_g` and `F_e` are gravitational and electrostatic forces between two electrons at a distance `0.1m` then `F_g//F_e` is in the order of
Answer» Correct Answer - ` 4.17 xx 10 ^(42)`

Discussion

20.	How far two electrons should be placed so that the force of repulsion between them is equal to the weight of an electron ?
Answer» Correct Answer - `5.083m`

Discussion

21.	When the terminals of a 100 V battery are connected to two large parallel plates 1 cm apart, a uniform field `vecE` is set up inside the region between the two plates. If the direction of the filed `vecE` is vertically upwards, determine the force on the electron in this field. Compare this force with the weight of the electron.
Answer» Correct Answer - `1.6 xx 10 ^(-19) N, 1.8 xx 10^(14)`

Discussion

22.	Two equal drops of water with the same and similar charge coalesce to form a large single drop. Show how the surface density, capacity, potential and energy change.
Answer» Correct Answer - `sigma_(1): sigma_(2)= 2^(2//3):2`

Discussion

23.	Three point charges are placed at the following points on the x-axis `: 2 mu C " at " x=0, -3 mu C " at " x=40 cm " and " -5 mu C " at " x=120` cm. Calculate the force on the `-3 mu C` charge.
Answer» Correct Answer - `0.15 N`

Discussion

24.	Two charged particles having charge `2.0xx 10^(-8)C` each are joined by an insulating string of length 1 m and the system is kept on a smooth horizontal table. Find the tension in the string.
Answer» Correct Answer - `3.6 xx 10^(-6)N`

Discussion

Explore topic-wise InterviewSolutions in .

Eight identical point charges of q coulomb each are placed at the corners of a cube side 0.1m. Calculate electric field at the centre of the cube. Calculate the field at the center when one of the corner charges is removed.

How many electrons are there in one coulomb of negative charge?

Obtain the dimensional formula of `epsilon_(0)`.

Calculate the coulomb force between two electrons separated by `0.8xx10^(-15) m`.

Two pith ball of mass 0.5 each are suspended from a common point O by means of silk threads, each of length 20 cm. When the balls are given equal and similar charges, they repel each other so that the two threads make an angle of `60^(@)` with each-other. Determine the charge on each ball.

Two small spheres each of mass m are suspended from a common point by threads 0.5 m long. They are equally charged and repel each other to a distance of 0.28m. If `=g10ms^(-2)`, what is the charge on each sphere?

If an oil drop of weight `3.2xx10^(-13) N` is balanced in an electric field of `5xx10^(5) Vm^(-1)`, find the charge on the oil drop.

Two particles (free to move) with charges `+q` and `+4q` are a distance L apart. A third charge is placed so that the entire system is in equilibrium. (a) Find the location, magnitude and sign of the third charge.(b) Show that the equilibrium is unstable.

Two pont chargees `q_(1) " and " q_(2) " of " 2xx10^(-8) C " and " -2xx10^(-8) C` respectively are placed 0.4 m apart. Calculate the electric field at the centre of the line joining the two charges.

Two charges, one `+5 mu C ` and another `-5 mu C` are placed 1 mm apart. Calculate the dipole moment.

Two point charges of `+2xx10^(-8) C` are placed 6 apart. Determine the force on a point charge of `+1xx10^(-8) C ` placed at a distance of 5 cm from each of the two given charges.

Determine the electric field produced by a helium nucleus at a distance of 1 Å from it.

A proton falls dwon through a distance of 2 cm in a uniform electric field of magnitude `3.34xx10^(3) NC^(-1)`. Determine (i) the acceleration of the electron (ii) the time taken by the proton to fall through the distance of 2 cm, and (iii) the direction of the electric field.

A positive charge of `20 mu C` is placed 2 m away from a negative charge of `20 mu C`. Determine the electric field at a point 2 m away from each charges.

Calculate the charge on an alpha particle. Given on a proton`=1.6xx10^(19) C`.

Calculate the charge on `._(26)F^(56)` nucleus. Given charge on a proton `=1.6xx10^(-19)` C.

If `F_g` and `F_e` are gravitational and electrostatic forces between two electrons at a distance `0.1m` then `F_g//F_e` is in the order of

How far two electrons should be placed so that the force of repulsion between them is equal to the weight of an electron ?

Two equal drops of water with the same and similar charge coalesce to form a large single drop. Show how the surface density, capacity, potential and energy change.

Three point charges are placed at the following points on the x-axis `: 2 mu C " at " x=0, -3 mu C " at " x=40 cm " and " -5 mu C " at " x=120` cm. Calculate the force on the `-3 mu C` charge.

Two charged particles having charge `2.0xx 10^(-8)C` each are joined by an insulating string of length 1 m and the system is kept on a smooth horizontal table. Find the tension in the string.