Lecture 6

1. Eight charges, each +q, are located symmetrically on a circle of radius R with P as its centre. If the charge at the position X is removed and brought to the location P, the force on this charge will be

from X to P

from P to X

from X to P

from P to X

2. Twelve charges are positioned on the dial of a wall clock such that a charge Q is at the position 1, 2Q at position 2, 3Q at 3 and so on, ending with 12Q at the position 12. If O is at the centre of the dial, what is the force exerted on a unit charge located at O, assuming the radius of the dial to be of unit length?

3. Two small conducting spheres attract each other electrostatically. It can be concluded that

At least one of the spheres is charged
Both the spheres are charged
Both the spheres are charged and their charges are of opposite sign
No definite conclusion on their charge state can be made from the given data.

4. Electric field lines are

Vectors in the direction of the electric force that acts on a test charge
Trajectories of a test charge in the electric field
Closed loops
Pictorial representation of electric field around a charged object.

5. The total amount of negative charge of all the electrons contained in one mole of water is approximately

1C
10⁵C
10⁶C
10²³C

6. A negative charge of 9C and mass 2kg orbits around a heavy positive charge of 16C in a circular orbit of radius 5m. What is the speed of the negative charge?

180 m/s
324 m/s
360 m/s
1984 m/s

7. A 2.5 C test charge is placed to the right of another charge Q. If there is an attractive force of 22.5 N between the two, what would be the force exerted if the magnitude of the test charge were to be doubled but it stayed at the same location as before?

90 N
45 N
11.25 N
d. Depends on the distance between the test charge and the charge Q.

8. The charges are kept at the corners A, B, C and D , respectively, of a square. If the force between the charges at A and B is F, the net force exerted on the charge at A due to the other three charges is

9. Two small conducting spheres of mass m and charge q each are suspended from a common point by means of threads. The spheres settle down to an equilibrium position, each making an angle with the vertical. The tension in either of the threads is

Zero

Greater than mg
Less than mg
Equal to mg

10. Two opposite charges are placed on the paper, as shown in the figure.
The charge on the left is three times as big as the charge on the right. Other than at infinity, where else can the force on a unit test charge due to these two charges is zero?

To the right of the smaller charge

Between the two charges
To the left of the bigger charge
Depends on the sign of the test charge.