6 Electrical fields

Question 1

fields

Answer 1

regions in which an object will experience a force at a distance

Question 2

electric field

Answer 2

created by charged objects

other charged objects in this electric field will experience force

Question 3

electric field strength

Answer 3

efs of an electric field at a point in space is defined as the force experienced per unit positive charge at that point
E=F/Q
efs= force/positive charge
NC-1

Question 4

efs direction

Answer 4

vector quantity- has direction, direction of the ef at a point is the direction in which a positive charge would move when placed at that point
electric fields point away from positive charges and towards negative charges

Question 5

electric field patterns

Answer 5

• arrow on an ef line shows direction of field
• ef lines are always at right angles to the surface of a conductor
• equally spaced, parallel ef lines represent a uniform field - one in which the efs is the same everywhere
• closer ef lines represent greater efs

Question 6

coulombs law

Answer 6

any two point charges exert an electrostatic (electrical) force on each other that is directly prop to the product of their charges and inversely prop to the square of the distance between them

Question 7

similarities between gravitational and electric fields

Answer 7

• point masses and point charges both produce radial fields

- similar equations for forces and field strengths

Question 8

differences between gravitational and electric fields

Answer 8

-masses always produce an attractive field, whereas charges can create both attractive and repulsive fields

Question 9

electric field between two parallel plates

Answer 9

produce uniform ef in region between plates
F=EQ
charge will gain energy as it moves from the positive plate to the negative plate
E=V/d
efs=pd/distance
Vm-1 (or NC-1)

Question 10

parallel plate capacitor

Answer 10

capacitance of a parallel plate capacitor depends on separation between plates, area of overlap between plates and insulator used between plates
C dir prop A/d
constant of proportionality in this relationship is the permittivity of free space

Question 11

uniform electric fields

Answer 11

A uniform field is a field which has no dependence upon position i.e. the field is constant in space.
A uniform electric field is produced between two parallel oppositely charged plates.
A particle between such plates is subject to a constant force no matter where it resides between the plates.

Question 12

electron acceleration between two charged plates

Answer 12

being neg charged, an electron between the plates will travel from the negative plate towards the pos plate, in the opposite direction of the ef.
the electron experiences a constant electrostatic force because of the uniform ef between the plates, so it has a constant acceleration

Question 13

electron travelling in direction of ef

Answer 13

from pos to neg plate

experiences deceleration

Question 14

charged particles moving at right angles to an ef

Answer 14

an object thrown horizontally on the surface of earth describes a parabolic path- its vertical motion is affected by the earth’s gravitational pull but its horizontal motion is unaffected.
this is the same when a charged particle enters a uniform electric field at a right angle

Question 15

electric potential

Answer 15

The electric potential at a single point can be defined as the work done per unit charge to bring a positive charge from infinity to that point.
The electric potential at infinity is often defined as 0.
V=E/q V=Q/4piE0r

Question 16

force-distance graphs for point and spherical charges

Answer 16

the force between two positive particles of charged Q and q varies with their separation
area under the graph is equal to work done
total work done is same as the electric potential energy E=Qq/4piE0r

Question 17

electric potential difference

Answer 17

epd between two points is just the difference between the potentials at these two points

Question 18

capacitance for an isolated sphere

Answer 18

a capacitor is a device that stores charge.
an isolated charged sphere of radius R also stores charge so must be a capacitor
the capacitance of a charged sphere is:
C=Q/V C=4piE0R

Question 19

equipotentials

Answer 19

an equipotential line is a line, or a surface, along which the electric potential is the same