SAT Fields

page 1


1. Two identical charges q are seperated by a distance r. The charges will repel with a force F.

If the distance between the charges is increased to 2r and both charges increased to 2q, the force will now be

  • A. F/4
  • B. F/2
  • C. F
  • D. 2F
  • E. 4F

2. Two plates hold identical and opposite electric charges, +Q and -Q, and are seperated by a distance d. What is the electric potential at the mid-point betwen these two plates?

  • A. 2Q
  • B. Q
  • C. Q/d
  • D. 2Q/d
  • E. zero

3. For the plates in question 2, what change to the charges and the plate seperation should take place to give the largest increase in the electric field strength?

  charge Q plate seperation d
increase decrease
decrease increase
increase increase
decrease decrease
increase stay the same


4. Electric field strength is defined as

  • A. the force per unit charge on a small positive charge
  • B. the force on a small charge
  • C. the force per unit charge on a unit positive charge
  • D. the force on a unit negative charge
  • E. the force on a small positve test charge


Four metal spheres P,Q, R and S are arranged in a square as shown. Each one has a charge of q or -q or zero.

5. The electric field at a point in the centre of the square will be zero if
  • A. All charges are positive
  • B. P and Q are positive, R and S are negative
  • C. P and Q are positive, R and S have no charge
  • D. P and R are positive, Q and S are negative
  • E. P is positive, Q R and S have no charge
A 2 mC charge is held between two charged plates. The plates have an electric field of 40 'units' between them.  

6. The unit of electric field strength E is

  • A. NC
  • B. NV
  • C. N/C
  • D. N/V
  • E. N2/C



7. The force on the charge due to the field will be

  • A. 20N
  • B. 80N
  • C. 0.02N
  • D. 0.08N
  • E. 0.025N
8. If the voltage between the 2 plates is 2kV, the work done in moving the charge from plate to plate is
  • A. 1 J
  • B. 4 J
  • C. 1 eV
  • D. 4 eV
  • E. 1 keV

A hollow metal sphere is charged to a high potential. The diagram below shows the electric field lines around the sphere.


9. A student is asked to add lines to the diagram to show the equipotential lines.

Which of the following statements about the equipotential lines is true?
  • A. they are circular
  • B. they are radial
  • C. they are parallel to eachother
  • D. they pass through the centre of the diagram
  • E. they are all equally spaced


10. Which of the following statements describes the field strength and the electric potential inside the hollow sphere?

field strength
greatest at centre
greatest at centre