Advertisements
Advertisements
Question
Justify your answers for each case.
State the significance of the negative value of electrostatic potential energy of a system of charges.
Three charges are placed at the corners of an equilateral triangle ABC of side 2.0 m as shown in the figure. Calculate the electric potential energy of the system of three charges.
Advertisements
Solution
U = `(KQ_AQ_B)/r + (KQ_BQ_C)/r + (KQ_CQ_A)/r`
U = `K/r[Q_AQ_B + Q_BQ_C + Q_CQ_A]`
U = `K/r xx [4 xx 10^-6 xx -4 xx 10^-6] + [-4 xx 10^-6 xx 2 xx 10^-6] + [2 xx 10^-6 xx 4 xx 10^-6]`
U = `K/r xx 10^-12[-16 - 8 + 8]`
U = `K/r xx 10^-12(-16)`
U = `(-9 xx 10^9 xx 10^-12 xx 16)/2`
U = -72 × 10-3 J
U = -7.2 × 10-2 J
A negative value signifies a stable system.
APPEARS IN
RELATED QUESTIONS
A cube of side b has a charge q at each of its vertices. Determine the potential and electric field due to this charge array at the centre of the cube.
Four point charges Q, q, Q and q are placed at the corners of a square of side 'a' as shown in the figure.
Find the
1) resultant electric force on a charge Q, and
2) potential energy of this system.
Find out the amount of the work done to separate the charges at infinite distance.
A point charge Q is placed at point 'O' as shown in the figure. Is the potential at point A, i.e. VA, greater, smaller or equal to potential, VB, at point B, when Q is (i) positive, and (ii) negative charge?
A point charge Q is placed at point O as shown in the figure. The potential difference VA – VB positive. Is the charge Q negative or positive?
Figure shows the field lines due to a positive point charge. Give the sign of potential energy difference of a small negative charge between the points Q and P.
If a charge q0 is there in an electric field caused by several point charges qi. The potential energy of q0 is given by ________.
In the circuit shown in figure initially, key K1 is closed and key K2 is open. Then K1 is opened and K2 is closed (order is important). [Take Q1′ and Q2′ as charges on C1 and C2 and V1 and V2 as voltage respectively.]
Then
- charge on C1 gets redistributed such that V1 = V2
- charge on C1 gets redistributed such that Q1′ = Q2′
- charge on C1 gets redistributed such that C1V1 + C2V2 = C1E
- charge on C1 gets redistributed such that Q1′ + Q2′ = Q
Calculate potential energy of a point charge – q placed along the axis due to a charge +Q uniformly distributed along a ring of radius R. Sketch P.E. as a function of axial distance z from the centre of the ring. Looking at graph, can you see what would happen if – q is displaced slightly from the centre of the ring (along the axis)?
Charges (+q) and (–q) are placed at points A and B respectively which are a distance 2L apart. C is the midpoint between A and B. What is the work done in moving a charge +Q along the semicircle CRD?
