Coulomb Forces and Electric fieldsThinking problems

Two fixed spheres, P and Q, have equal butopposite charges on them. A third sphere, positively charged, is movedwitha constant speed in the direction of the arrows along each of the paths ( i ) and ( ii) as shown. The following diagrams show possible variations of F, the y component of the electrostatic force on this third sphere, as functions of time.

Use these diagrams to give the best answer to each of the questions

Question 1 (1970 Q62)

How wouldFY vary with time for path (i)?

Question 2 (1970 Q63)

How wouldFYvary with time for path (ii) which perpendicularly bisects the line joining P andQ ?

Two small identical metal spheres A and B carry equal positive charges +Q so that they repel each other with a force of 4 x 10-5newton when placed a distance dapart.

A third identical sphere C, also carrying a charge +Q, is placed on the line joining A and B as shown.

Question 3 (1970 Q64)

What is the value of the electrical force on C? Specify the direction of the force.

The charge on A is now made equal to -Q.

Question 4 (1970 Q65)

What is the value of the electrical force now on C? Specify the direction of the force.

Question 5 (1970 Q66)

In the situation shown in the last diagram, a fourth identical metal sphere D carrying a charge -Q. is touched in turn onto A, B and C. In terms of Q, what is the final charge on D? Specify the sign of the charge.

Two large parallel metal blocks are set up 0'1 metre apart in a vacuum. A battery of EMF 360 volt is connected across the blocks so that the block on the left is positively charged and the other one negatively charged.

P is a point 0.02 metre from the positive block. Q andR are points 0.02 metre from the negatively charged block. The distances PQ and QR are both 0.06 metre.

Experiments are performed using a proton and an alpha particle.

An alpha particle has twice the charge and four times the mass of a proton.

Question 6 (1970 Q67)

What is the value of the ratio:

?

Question 7 (1970 Q68)

What is the value of the ratio:

?

Question 8 (1970 Q69)

What is the value of the electric field between the blocks?

Question 9 (1970 Q70)

Which of the following graphs best represents the electric potential at all points along the straight line between X and Y?

A large, uncharged metal sphere is moved towards a small, charged metal sphere.

Question 10 (1971 Q67)

Which graphbest represents the relation between the electrical force and the separation between the centres of the spheres?

The two spheres are now touched together.

Question 11 (1971 Q68)

When the spheres are separated, which graph best represents the force-distance relation?

A network of four different wires of equal length is connected to a battery as shown.

Question 12 (1971 Q69)

Which graph best represents the electric field versus distance relation around the circuit?

Question 13 (1971 Q70)

Which graph best represents the electric potential versus distance relation around the circuit?

Question 14 (1971 Q71)

Which graph best represents the current versus distance relation around the circuit?

Question 15 (1971 Q72)

What would happen in the circuit if T and V were connected by a wire of zero resistance?

A. Theoretically, there would be an infinite current in the circuit; in practice, the battery wouldbe short-circuited, and quickly lose its store of energy.

B. The current in TUV would fall to zero, and the current in VWX would increase.

C. The current in UV would be doubled, and the current in VW halved.

D. The current in both UV and VW would decrease.

E. There would (theoretically) be an infinite current in TV.

F. There would be no change in the currents in the circuit.

A current of 6.0 amp flows through a piece of wire of length 0. 50 m connected to a 1.5 volt battery.

Question 16 (1971 Q73)

What is the electric field in the wire?

Question 17 (1971 Q74)

How much power is dissipated in the wire?

Question 18 (1971 Q75)

What current would flow through a piece of wire of the same material and thickness but double the length when connected to the same battery?

Charges of +q, +Q and +3Q arc placed as shown'

The force on +q due to +Q alone is F.

Question 19 (1972 Q63)

In terms of F, what is the magnitude of the resultant force on +q due to both +Q and +3Q?

A student carries out the Millikan experiment with small plastic spheres, all of the same size.

He measures the terminal velocities of several spheres under two conditions, one when the electric field is in the same direction as gravity, and one when the field is reversed. He displays his results as shown in the diagram.

The letters refer to particular spheres.

Question 20 (1972 Q64)

Which sphere carries the greatest charge?

Question 21 (1972 Q65)

Which sphere carries no net charge?

Question 22 (1972 Q66)

Which sphere is apparently of different mass from the others?

Question 23 (1972 Q67)

How many electronic charges appear to be on the sphere G?

In the Millikan experiment a student measures the velocities of small spheres between two charged parallel plates. The velocities are measured twice for each sphere, with the electric field first in one direction and then in the other.

Question 24 (1973 Q63)

Which sphere is uncharged?

Question 25 (1973 Q64)

Which sphere has different weight from the others?

Question 26 (1973 Q65)

Which sphere appears to carry charge of magnitude one electric charge?

Question 27 (1973 Q66)

What would A's velocity be if the plates were uncharged?

X and Y are two wires, each of uniform cross-section and having the same length.

Question 28 (1973 Q73)

Which of the graphs below represents the electrical potential versus distance along each wire?

Question 29 (1973 Q74)

Which graph represents the current versus distance along each wire?

Question 30 (1973 Q75)

Which graph represents the electric field versus distance along each wire?

Question 1A

Question 2F

Question 32.7 x 10-4 N

Question 44.5 x 10-4 N

Question 5+Q/2

Question 62

Question 71

Question 83600 Vm-1

Question 9E

Question 10A

Question 11D

Question 12A

Question 13B

Question 14C

Question 15B

Question 163.0 Vm-1

Question 179.0 W

Question 183.0 A

Question 195F/4

Question 20I

Question 21C

Question 22E

Question 235

Question 24B

Question 25E

Question 26F

Question 27-4

Question 28F

Question 29C

Question 30D