chapter 22 - Electric fields Flashcards
What is an electric field?
A region of space where a charge will experience an electrostatic force.
What is the definition of electric field strength?
The force per unit charge on a positive test charge placed at that point
What are the units of electric field strength?
NC⁻¹ (or Vm⁻¹)
What does ε0 represent?
permittivity of free space ( 8.85x10^-12)
What does εr represent?
Relative permittivity (of a dielectric).
What does the direction of an electric field line show?
The direction of the force exerted on a positive test charge.
What does the spacing of electric field lines show?
Field strength.
Are test charges positive or negative?
positive
What units equivalent to Vm⁻¹
N C⁻¹
When is the equation E = V/d used?
To find the uniform field strength between two parallel plates.
What is a dipole?
A pair of opposite sign charges separated by a small distance (e.g. a polar molecule like HCl)
State Coulomb’s law in words.
The force between two point charges is proportional to the product of the two charges and inversely proportional to the square of their separation distance.
What is electric potential difference?
The work done per unit positive charge in moving between two points
What is the definition of absolute electric potential of a point?
The work done per unit positive charge to move from infinity to that point in the field.
What is the absolute electric potential an infinite distance from a 1C charge?
0
What units are equivalent to a V?
J C⁻¹
What is the relationship between the electrostatic force between two point charges and their seperation distance?
It is inversely proportional to the square of separation OR inverse square law
What is the relationship between the electric potential and distance from a point charge?
electric Potential α 1/distance
What is a uniform electric field?
A region of space in which the electric field strength is the same at all points
What is a radial field?
An electric field generated by a point charge OR a field that obeys the inverse square law.
What is a neutral point in an electric field?
A point at which the resultant field strength is zero
Is electric field strength a vector or a scalar quantity?
Vector
Is electrical potential a vector or scalar quantity?
Scalar
State a similarity between electric and gravitational fields.
Both obey inverse square law for field strength (around a point mass/charge). Both have infinite range. Both act between two objects at a distance.
State two differences between electric and
gravitational fields?
Gravitational fields act on masses, electric fields on charges: electric fields are much stronger that gravitational fields: electric fields can be attractive or repulsive, gravitational fields are always attractive: potential is always negative in a gravitational field.
When is the equation V = Q / (4 pi ε0 r) used?
To find the potential around a point charge/in a radial field.
When is the equation C = 4 x pi x ε0 x R used?
To calculate the capacitance on an isolated sphere.
What is represented by R in the equation C = 4 x pi x ε0 x R used?
The radius of an isolated sphere.
What is the relationship between electric potential energy and electric potential?
EPE = V x q where q is the charge in the field.
explain a practical to detect electric fields?
hang a uniformly charged sphere from a nylon thread, attach thin strip of gold foil to the bottom of a insulator, charge this gold foil by momentarily touching it on charged sphere, the charged foil will experience a electrostatic force when close to sphere and as they are both positive they will repel. the angle of the gold foil shows the electric field strength
describe a practical to investigate coulombs law?
charge two metal balls attached to rods by momentarily touching them to a positive electrode. attach one two the top of a sensitive measuring balance (measuring scale) and then lower the other one down from above. record the distance (r) between balls and also reading on the balance. change r and measure results again. force should be inversely proportional to r^2
