Electric Charge and Electric Field
Static Electricity; Electric Charge
- Objects such as hard rubber, glass rod, or plastic ruler rubbed with cloth will display an effect known as static electricity.
- An object becomes "charged" as a result of rubbing and it possess a net electric charge; but it can also be "dis-charged" or neutral when it's grounded. (Earth is often referred to as a "sea of electrons")
- key concept: unlike charges attract; like charges repel (two types: positive/negative)
- law of conservation of electric charge: the net amount of electric charge produced in any process is zero; no net electric charge can be created or destroyed
Therefore if one object acquires a positive charge, then it is expected that an equal amount of negative charge will be found in neighboring areas.
- An object becomes "charged" as a result of rubbing and it possess a net electric charge; but it can also be "dis-charged" or neutral when it's grounded. (Earth is often referred to as a "sea of electrons")
- key concept: unlike charges attract; like charges repel (two types: positive/negative)
- law of conservation of electric charge: the net amount of electric charge produced in any process is zero; no net electric charge can be created or destroyed
Therefore if one object acquires a positive charge, then it is expected that an equal amount of negative charge will be found in neighboring areas.
Insulators and Conductors
- Materials such as iron nails are conductors of electricity
- wood and rubber are considered nonconductors/insulators
- However, few materials such as silicon and germanium, are semiconductors
- Some electrons are bound very loosely and can move about freely within the material: free electrons or conduction electrons
- "Charging by conduction"- or by contact is when two objects end up with the same sign of charge
- One way to induce a net charge on a metal object is to connect it with a conducting wire to the ground (grounded or earthed)
- wood and rubber are considered nonconductors/insulators
- However, few materials such as silicon and germanium, are semiconductors
- Some electrons are bound very loosely and can move about freely within the material: free electrons or conduction electrons
- "Charging by conduction"- or by contact is when two objects end up with the same sign of charge
- One way to induce a net charge on a metal object is to connect it with a conducting wire to the ground (grounded or earthed)
Electroscope
- electroscope: is a device that can be used for detecting charge (ex. inside a case, two movable metal leaves can be split apart when a conductor is connected to the metal knob on the outside)
- electroscopes can be charge by induction or conduction.
- a previously charged eletroscope can be used to determine the sign of a charged object.
- electroscopes can be charge by induction or conduction.
- a previously charged eletroscope can be used to determine the sign of a charged object.
Coulomb's Law
- It gives the magnitude of the electric force (F) that either object exerts on the other
- The direction of the electric force is always along the line joining the two objects.
- If two objects have the same sign, they repel. If two objects have opposite signs, they attract.
k = 8.988 x 10^9 Nm^2/C^2
- electric charge is said to be quantized (1e, 2e, 3e, etc.)
- if several charges are present, the net force on any one of them will be the vector sum of the forces on that charge due to each of the others.
- The direction of the electric force is always along the line joining the two objects.
- If two objects have the same sign, they repel. If two objects have opposite signs, they attract.
k = 8.988 x 10^9 Nm^2/C^2
- electric charge is said to be quantized (1e, 2e, 3e, etc.)
- if several charges are present, the net force on any one of them will be the vector sum of the forces on that charge due to each of the others.
Electric Field
- The electric field at any point in space, is defined as the force (F) exerted on a positive test charge placed at that point divided by the magnitude of the test charge q: E=F/q
- When calculating electric force from two different points, the force of the charges and it's angles can be treated like vectors. Calculate the x, y components separately and then combine it for the resultant force.
- When calculating electric force from two different points, the force of the charges and it's angles can be treated like vectors. Calculate the x, y components separately and then combine it for the resultant force.
- Field lines show the direction of the electric field: the field points in the direction tangent to the field line at any point.
- Lines are drawn so that the magnitude of the electric field is reflected proportional to the number of lines crossing unit area perpendicular to the lines.
- The lines start with positive charges and end with negative charges. (electric field lines never cross)
- Lines are drawn so that the magnitude of the electric field is reflected proportional to the number of lines crossing unit area perpendicular to the lines.
- The lines start with positive charges and end with negative charges. (electric field lines never cross)
Graphic Organizer
Here is a general visual of this chapter's concepts.