charging by contact 2: conduction

Charging by Contact 2:CONDUCTION

• Name two ways that objects can receive an electric charge.

• Describe how a material can be charged by contact (conduction).

KEY WORDSConduction Pith ball

Charge separation Electroscope

Particle model for electrostatics

Because of the ability of electrons to move, it is possible to induce a charge separation in objects.

This works better for some materials (conductors)than others (insulators).

Charge separation is deliberate movement of electrons to one part of a material.

It is responsible for most attraction forces seen in objects.

Electrons move - causes charge separation.

Attraction

Electroscope is a tool for determining whether or not an electrical charge is present in an object.

It can provide 3 kinds of measurement:

• detect the presence of an electrostatic charge.• determine the type of charge on an object.• determine the amount of charge on an object.

We will use two kinds: pith ball electroscopes and foil electroscopes (Pith is a light plant material).

Charged object moves away – electrons redistribute - leaves fall back down.

2. Conduction• Electric charge can travel by touching a charged object to a neutral object.• Results in a neutral object gaining a charge.

Electrons move towards the more positive object - imparting charge.

1. Triboelectric Charging• Two neutral objects are rubbed together, which

transfers electrons resulting in charged objects.

4. Charge transferred to pith - same as rod. (repulsion)

1. Charged rod.

2. Charge separation in pith ball (attraction)

3. Pith touches rod – electrons move towards positives.

e-

Negative charge (excess e-)

Negative charge (excess e-)

CONDUCTION – with (-) rod

4. Charge transferred to pith - same as rod. (repulsion)

1. Charged rod.

2. Charge separation in pith ball (attraction)

3. Pith touches rod – electrons move towards positives.

e-

Positive charge (lost e-)

Positive charge (lost e-)

CONDUCTION – with (+) rod

Particle model of electrostatics:• Charge is a particle that is conserved – can’t be created or destroyed.

• Two kinds of charge - positive and negative / attraction and repulsion.

• Neutral objects have equal numbers of positive and negative charges.

• Only negative charges move.

• Two neutral objects can be charged by rubbing (friction) against each other – triboelectric charging.

• Charged object can charge neutral object by touching – conduction.

• Materials, which allow charges to move easily, are called conductors. Materials in which charges do not move easily are called insulators