Electric fields Flashcards
what is an electric field
an area where an object with charge experiences a force of attraction or repulsion
whats an example of a radial electric field
a point charge (electron)
whats an example of a uniform electric field
a field between two charged plates (capacitor)
what are electric field lines
the direction of the force acting on a positive charge at that point in the field, they always point towards negative
what are electric field lines in a uniform field
follow the same principal but if both plates are positive they will go to the least positive plate
what are rules to follow when drawing electric field lines
draw arrows on lines (away from negative)
the stronger the charge- the more lines
if charges are the same- they should deflect away-
a vertical line between which should be closer to weaker charge
what is coulombs law
its mathematically the same as newtons. for an electric force around two objects
-its proportional to the product of the charges
-its inversely proportional to the distance between squared
-its attractive or repulsive
what is electrical field strength
the force on an object per unit positive charge
what are the three scenarios when electric field strength varies with distance graphically
- a radial field around a charged sphere (van der Graaf)
-a radial field around a point charge (electron r=0)
-a uniform field
(century to check graph drawing)
what happens when a charged particle enters an electric field
they will experience a constant force in on direction. therefore they will follow a parabolic path. (same principal as a projectile)
whats a real life example of a charged particle entering an electric field
old tv-screens and computer monitors.
the first uniform field accelerates the electrons and the second field deflects them up or down. (check century)
what is thermionic emission
when a wire gets hot and releases free electrons
what is electric potential
the energy required (work done) to move a positive 1C charge from infinity to a point in the field
how to draw more complex equipotential lines on electric field lines
always remember they are at right angles to the field. draw small lines at 90 degrees at each point and draw curves to join them
how do you draw electric potential energy against distance on a graph
both 1/x
negative-potential starts negative
positive- potential starts positive
what does the gradient mean of an electric potential against distance
draw a tangent
the gradient is electric field strength
what is electrical potential difference
if you want to move closer or further from another charge work needs to be done, you need to move between equipotential lines.
for every coulomb you want to move will take xJ amount of energy to move it between the points
how do you calculate electrical potential energy from a graph
the area underneath a electrical field strength against distance graph
what are the similarities and differences between gravitational and electric fields– forces
similarities
-radial fields involve inverse square law
-uniform fields have constant force at all points
differences
-G is only attractive, E is attractive and repulsive
-G forces are usually much smaller than E forces
what are the similarities and differences between gravitational and electric fields– field strength
similarities
-both involve inverse square law
-both defined as force per unit …
differences
-1kg is small in Gravitational per 1C is large in electric
-G is always directed towards mass but E is directed away from positive toward negative
what are the similarities and differences between gravitational and electric fields– potential
similarities
-defined as work done moving 1… from infinity to a point in the field
-in a uniform field, potential varies linearly with distance
differences
-gravitational is always negative but electric is negative for negative charges and positive for positive charges
