PHYS 2212 Module 1.2

Conductors, Insulators, and Charging by Induction

Recommended Reading

1.2 Conductors, Insulators, and Charging by Induction

Learning Objectives

By the end of this section, you will be able to:

  • Explain what a conductor is
  • Explain what an insulator is
  • List the differences and similarities between conductors and insulators
  • Describe the process of charging by induction

Electric Charge and Charging by Induction

Practice!

Practice 1.2.1

Consider three plastic balls (A, B, and C), each carrying a uniformly distributed charge equal to either +Q, -Q or zero, and an uncharged copper ball (D).

A positive test charge (T) experiences the forces shown in the figure when brought very near to the individual balls. The test charge T is strongly attracted to A, strongly repelled from B, weakly attracted to C, and strongly attracted to D.
Check your answer here: strongly attractive
Practice 1.2.2

Consider three plastic balls (A, B, and C), each carrying a uniformly distributed charge equal to either +Q, -Q or zero, and an uncharged copper ball (D).

A positive test charge (T) experiences the forces shown in the figure when brought very near to the individual balls. The test charge T is strongly attracted to A, strongly repelled from B, weakly attracted to C, and strongly attracted to D.
Check your answer here: weakly attractive
Practice 1.2.3

Consider three plastic balls (A, B, and C), each carrying a uniformly distributed charge equal to either +Q, -Q or zero, and an uncharged copper ball (D).

A positive test charge (T) experiences the forces shown in the figure when brought very near to the individual balls. The test charge T is strongly attracted to A, strongly repelled from B, weakly attracted to C, and strongly attracted to D.
Check your answer here: attractive
Practice 1.2.4

Consider three plastic balls (A, B, and C), each carrying a uniformly distributed charge equal to either +Q, -Q or zero, and an uncharged copper ball (D).

A positive test charge (T) experiences the forces shown in the figure when brought very near to the individual balls. The test charge T is strongly attracted to A, strongly repelled from B, weakly attracted to C, and strongly attracted to D.
Check your answer here: neither attractive nor repulsive
Practice 1.2.5

Two uncharged metal spheres located on top of insulating poles are initially in contact as shown.  A positively charged insulator is brought close to sphere 1 without touching and removed, and then the spheres are separated.
Check your answer here: Q1 = 0 and Q2 = 0
Practice 1.2.6

Two uncharged metal spheres located on top of insulating poles are initially in contact as shown.  A positively charged insulator is brought close to sphere 1 without touching and then the spheres are separated before the positively charged insulator is removed.
Check your answer here: Q1 = – and Q2 = +

Discuss!

Reflect on this question and take notes on how you would answer it. Then we will share these thoughts together in a class discussion.

Two identical conducting spheres, one carrying charge +q and the other carrying charge +3q, are initially held a distance d apart. The spheres are allowed to touch briefly and then are returned to separation distance d.  Is the magnitude of the force they exert on each other after touching greater than, smaller than, or the same as the magnitude of the force they exerted on each other before touching?