Electric Fields Flashcards
What is a force field ?
A field is a region where each point is affected by a non- contact force.
What did Richard Feynman describe a field to be ?
Something that has the potential to produce a force.
What is an electric field ?
A region where a charge is affected by the electrostatic force
What is a difference between the gravitational field and electric field ?
Gravitational fields are always attractive unlike electric fields which are attractive and repulsive depending on the charges in the field
What does Coulomb’s law state ?
Any two objects with a charge will experience a force inversely proportional to the square of the distance between them and directly proportional to the product of the two charges
Which fields follow the inverse square law ?
Gravitational and electric fields
What is the force produced when there are two objects ?
F= k Qq/ r^2
What is the constant k in F = k Qq/r^2 ?
1/4 pi epsilon0 = 8.99*10 ^9
What is permittivity ?
A measure of how difficult it is to generate an electric field within a material
If a material has a higher permittivity would it be harder or easier to generate an electric field?
It would be harder to generate an electric field as they are better insulators
What is the permittivity of free space?
The permittivity of the air
How can you calculate the electric field strength ?
E= kQ/r^2
What is the electric field strength ?
The electric force exerted per unit positive charge at a point within the field
What do you get when you substitute E (electric field strength) within columbs law equation ?
F=Eq
What do electric field lines show ?
They convey the direction of force experienced by a positive charge placed in the field
What will the resultant field be when the electric fields are in the same direction ?
E1 +E2
What will the resultant field be if the electric fields are in opposite directions ?
E1-E2
What are the factors that impact the direction of the resultant field ?
-the type of charge (like charge .. )
- the magnitude of the charges
Where to radial electric fields exist ?
Between point charges and around uniform spheres
How can you tell that the fields get weaker as the distance increases from point charges ?
The field lines separation increases (weaker )
Where do uniform electric fields typically exist ?
Between charges metal plates and electrodes
What are the field lines like in a uniform electric field?
They would be parallel lines that are equally spaced
What is the difference in force experienced within a radial and uniform field.
The force experienced in a uniform electric field is constant throughout whereas in a radial field the force decreases as the distance increases
How do you dare field lines in an electric field ?
From the positive to negative and perpendicular to the component
What is the null point ?
A point within the field where the resultant force and the field strength is 0
What happens when a charged particle (an electron) interacts with an uncharged particle?
The electron would repel the negative charges pushing them away and the positive charges closer to the surface
How can you calculate the electric field strength for a uniform field ?
E=V/d
- Work done by the field from moving the charge from one plate to another (W=Fd )
-electric potential difference ( the work done per unit charge in moving the charge between two points (W/q =V ) (w= qV ) - Fd =qV
Sub F = Eq gives us E= v/d
What are the two units for the electric field strength ?
Vm^-1 and Nc^-1 (newtons per columb )
What happens if a charged particle is placed in an electric field ?
The particle will experience a force that will cause it to accelerate
What happens if a positive charge at rest had been placed in a uniform electric field ?
It will move parallel along the field line
What happens if a negative particle at rest had been placed in a uniform field ?
It will accelerate in parallel against the field lines
What happens if a charged particle in motion is placed within a uniform field ?
It will experience a constant electric force (uniform ) travelling in a parabolic shape (trajectory ) depending on the charge of the particle
What are the factors affecting the deflection when a charged particle in motion travels through a uniform electric field ?
- greater mass - smaller deflection
-greater the charge - the greater deflection - greater speed - less deflection
What is electric potential ?
The work done /potential energy per unit positive charge to move a positive charge from infinity to a point within the field (against the field )
What is the electric potential at a distance of infinity?
0
How can you work out the electric potential of a point ?
V= W / q = kQ/ r
When is the electric potential positive ?
When work is done against the field ( like charges reppel) positive charge
When is the electric potential negative ?
When work is done by the field ( opposite charges attracting ) negative charge
What is the gradient of a v against r graph ?
The electric field strength
For a negative charge as r increases what happens to the potential ?
The potential increases
What does the area under an electric field strength against r graph give ?
The electric potential -change in potential from r1 to r2
