13. Electric Field Flashcards
for any point outside a charged spherical conductor, the charge on the sphere may be considered to act as a point charge in the centre.
by reference to electric field lines, explain this
electric field lines are radial/ normal to surface
electric field lines appear to originate from the centre of the sphere
suggest why it may be assumed that the proton and the nucleus behave as charges when using Coulomb’s law
radii of proton and nucleus are very small compared to distance between them
suggest why electric field strength is zero inside metals
charges in metal do not move
no resultant force on charges so no electric field
explain whether a plastic sphere can be at equipotential throughout the sphere
plastic is an insulator/ not a conductor/ does not have free electrons
charges do not move inside an insulator
so no single value for potential
[imagine graph curved, as r decreases EPE decreases/ becomes more negative]
is the mass positively charged or negatively charged?
as r decreases, energy decreases (OR work got out due to attraction)
attraction, so point mass is NEGATIVELY charged
gradient at a point on the electric potential energy-distance graph is G
show that electric field strength E at this point due to the charged point mass is given by Eq=G, where q is the charge at this point
electric potential energy = charge x electric potential (V=qU)
electric field strength E is electric potential gradient
electric field strength E = gradient of potential energy graph / charge (since F=qE)
state one similarity and one difference between the electric field lines and gravitational field lines around an isolated positively charged metal sphere
similarity: lines are radial
diff: gravitational lines are directed towards the sphere, electric lines are directed away from the sphere
the definitions of electric potential and of gravitational potential at a point have some similarity
state one similarity between the 2 definitions
ratio of work done to either mass or charge
OR
work done per unit mass or charge in moving either small test mass or charge from infinity
OR
both have zero potential at infinity
explain why values of gravitational potential are always negative whereas values of electric potential may be positive or negative
gravitational forces are always attractive, electric forces can be attractive or repulsive
for gravitational, work got out as masses come together from infinity
for electric, work done on charges if same sign; work got out if opposite sign as charges come together from infinity
describe pattern of field lines (lines of force) between plates
straight lines AND from positive to negative plate
state what is meant by a field line (line of force) in an electric field
represents direction of electric force on positive charge
by reference to an atom in the air, suggest the mechanism by which the electric field causes the air to become conducting
electrons are stripped off the atoms
electrons and positive ions move in opposite directions
giving rise to a current
explain a situation where a small test charge is moved from a point to another in the field, the net work done is zero
both points are at equal electric potential
work done = qΔV
ΔV=0 so no work done
state the relationship between electric potential and electric field strength at a point
field strength = -ve potential gradient
explain why calculations involving motion of atomic particles in a uniform field between parallel plates do not need to include gravitational effects on the electron
electric force is much greater»_space; than gravitational force on electron
OR
acceleration due to electric field is much more greater»_space; than acceleration due to gravitational field
