6.2: Electric Fields, F Flashcards
Define: Electric field
Region around a body in which other charged bodies feel a force due to the electric charge around the body
Define: Electric field lines
Shape of the field and direction of the field lines at a point is the direction in which a small positive charge would move when placed at that point
Define: Electric field strength
Force per unit positive charge (E=F/Q)
-Force that a charge of +1C would experience if it was placed in the electric field
Describe the force between 2 opposite charges
If the charges are opposite then the force is attractive and the forces will be negative
If they are like charges then the force is _________ and the force will be ________
If they are like charges then the force is repulsive and the force will be positive
What relationship(/law) can be used to describe the distance of the charges and the force between them
- Inverse square law.
- The further apart the charges are, the weaker the forces between them
What factor does the force F depend on? (in terms of electric field)
-Permittivity of the material between the two charges
ε0
Define: Coulomb’s law
Electrical force F between two point charges is directly proportional to the product of their charges and is inversely proportional to the square of their separation
(F=Qq/4πε0r^2)
How can a uniform electric field be produced
By connecting two parallel plates to the opposite poles of a battery
Describe the field strength between two parallel plates
Field strength(E) is the same at all points between the two plates
What does the Capacitance of a capacitor depend on?
-How easy it is to generate an electric field between 2 plates
-Depends on the dimensions of the capacitor
(C=ε0A/d)
Describe the movement of charged particles through a uniform electric field
They move through uniforms fields like projectiles, where a particle of charge Q will experience a constant force (F=EQ)
Describe the direction of travel (force acting upon) a charged particle will move in relation to field lines in a uniform electric field
- Positively charged = force is in the same direction as field lines (acceleration)
- Negatively charged = force is in the opposite direction to the field lines (acceleration)
Describe the path a charged particle would take as it travels at an angle through a uniform electric field
Since the perpendicular components are independent = constant velocity in direction of field but an acceleration in the direction of field (Newton’s first law) ∴ creating a parabolic path
Explain how an application of Newton’s second law in relation to uniform electric fields
Work done on a particle by the force (of the field) increases kinetic energy causing it to accelerate at a constant rate in the direction of the force (Newton’s 2nd law)
Define: Permittivity
A constant (e) related to the size of the capacitance C of a capacitor.
Define: Relative permittivity
A material which is the factor by which the capacitance of a capacitor (NOT COMPLETE)
Define: Electric potential(V)
Work done per unit positive charge to move that charge from infinity to a point in the electric field
V=Q/4πε0r
Define: Electric potential energy
Work done to move that charge from infinity to a point in an electric field
E=Qq/4πε0r
Derive an expression for the capacitance of an isolated charged sphere(,assuming charge is evenly distributed)
- V=Q/C and V=Q/4πε0R, R= radius of sphere
- Q/C = Q/4πε0R ,cancel Q’s
- 1/C = 1/4πε0R
- C = 4πε0R
What assumption is made when deriving the capacitance of an isolated charged sphere
As it is a charged sphere all the charge is concentrated in the centre ∴ we can treat it like a point charge
List 3 differences between Gravitational fields and electric fields
- Gravitational fields are always attractive
- Objects can be shielded from an electric field
- Size of an electric field depends on the medium between the charges
List 3 similarities between Gravitational fields and electric fields
- g is force per unit mass, E is force per unit positive charge
- Inverse square law
- V is zero at infinity
