Target: 10 Questions in 10 minutes

An IB Physics data booklet is helpful

 1. Which of these diagrams correctly shows the electric field between positive and negative charges? (Only a few lines are shown here).

2+3: Two charges +Q are separated by a distance r. There is a repulsive force F acting between the 2 charges as shown:

2. What is the size of the force if the charges are moved to a distance of ½ r?

• A. ¼ F
• B. ½ F
• C. 2 F
• D. 4 F

3. Which of these changes to the diagram above would increase the force to 6F?

• A. Increase the original distance to 3r.
• B. Decrease the original distance by a factor of 3.
• C. Keep the original distance, but increase both charges to + 3 Q.
• D. Keep the original distance, but increase both charges to + √6 Q.

4. Electric field strength is defined as ...

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

5. At which point in this diagram is the electric field due to the 2 charges equal to zero?

6. The sign of the right hand charge has now been reversed. At which point in this diagram is the electric field zero?

7+8: These questions are about the field between parallel charged plates.

7. Which of the following diagrams correctly shows the electric field between parallel charged plates?

8. The plates above are held at a constant potential difference, and then moved closer together. How will this affect the electric field strength and the spacing between field lines (the field line density) in the correct diagram above?

9. Millikan carried out an experiment with charged oil droplets suspended between charged plates that produced an electric field. What was detemined using this experimental procedure?

• A. The basic unit of electric charge was quantised.
• B. The electron has a negative charge.
• C. The electric field strength between charged plates.
• D. Coulomb's law for the force between charges.

10. A plastic rod is charged using friction with a cloth. The positively charged rod is now held over a neutral metal plate. The plate is then briefly earthed using a wire, leaving the metal plate with an induced charge.

Which of these sentences correctly describes the earthing process?

• A. Negative charges flow from the plate to earth leaving the plate with a positive charge.
• B. Positive charges flow to from the plate to earth leaving the plate with a negative charge.
• C. Negative charges flow to from earth to the plate leaving the plate with a negative charge.
• D. Positive charges flow to from earth to the plate leaving the plate with a positive charge.