Radial Electric Fields

Question 1

what do the field lines of a positively charged particle look like

Answer 1

• the lines are drawn perpendicular to the surface of the particle
• they would all be equidistant from each other
• with arrows pointing outwards

Question 2

what does the distance between the field lines represent

Answer 2

the strength (potential) of the field

Question 3

how do the field lines accurately represent the field strength of a particle

Answer 3

• the further you get away from the particle, the further the lines get from each other
• which correctly indicates a decrease in the field strength the further you get from the particle

Question 4

what does a decrease in field strength mean about the change in potential

Answer 4

the potential would change less quickly

Question 5

what do the field lines of a negatively charged particle look like

Answer 5

• the lines are drawn perpendicular to the surface of the particle
• they would all be equidistant from each other
• with arrows pointing inwards

Question 6

why do we know there is no electric field within a charged sphere

Answer 6

because the charged particle feels no resultant force when on its own

Question 7

why is there no resultant force within the sphere

Answer 7

the overall effect of the all the charges and their directions cancel out

Question 8

where should you start distance measurements on the sphere when carrying out calculations

Answer 8

from the centre

Question 9

what type of fields do spherical objects create

Answer 9

radial fields

Question 10

what is the equation for calculating the radial field strength at a distance r from a charge Q

Answer 10

E = Q / 4 pi e(0) r^2

Question 11

what is the constant e(o), which is actually the fancy sigma (backwards 3)

Answer 11

• the permittivity of space

- e(0) = 8.85x10-12 Fm-1

Question 12

why does this equation technically only apply to fields produced in a vacuum

Answer 12

• because of the constant e(0)
• it relates to the ability of the fabric of the universe to support electric fields
• but air is considered to be close enough

Question 13

how would we account for more extreme media like an electric field being produced in water

Answer 13

• we would use the relative permittivity of that medium

- given the symbol e(r)

Question 14

what does electric field strength tell us (relating back to potential)

Answer 14

how quickly the electric potential is changing

Question 15

what would a stronger field therefore have

Answer 15

equipotentials closer together

Question 16

what would you write an equation showing the electric field strength is equal to the rate of change of potential (V) with respects to the distance (x)

Answer 16

E = -dV / dx

Question 17

what is the equation for radial field potential at a distance r from a charge Q

Answer 17

V = Q / 4 pi e(0) r

Question 18

how would you calculate the electric potential at a distance of 1 angstrom (1x10-10 m) from a proton

Answer 18

• using the V = equation
• Q would be the charge of a proton
• which is equal to the charge of an electron
• so Q = 1.6x10-19, then you would just input the other values

Question 19

what kind of shape is most ideal for concentrating charge at one point

Answer 19

spikes

Question 20

why are spikes / pointed shapes ideal

Answer 20

• because they would have close field lines due to their low surface ares
• so the field around them would be strong

Question 21

how to lightning conductors shaped like this protect buildings

Answer 21

• the concentrated charge on the conductors attract opposite charges more strongly
• so lightning is more likely to hit them than the building
• the field can even be strong enough to cause a charge leakage through the conductor
• if this happens before charge builds up to the point of a lightning strike
• the chances of having one is reduced which further protects the building

Question 22

what would the field lines of a proton being attracted to an electron look like

Answer 22

• the lines would connect at the centre
• still being perpendicular to the surface of both particles
• the centre line would therefore be straight while the others would be curved
• the arrows would be pointing from the +ve to -ve
• with both particles having arrows pointed towards and into them from the back, still perpendicular

Question 23

what would the field lines of a proton being repelled by another proton look like

Answer 23

• all lines would be perpendicular from the surface
• but the lines would curve upwards or downwards to avoid each other
• the arrows would still be pointing outwards (as well as the lines at the back)

Question 24

what would the field lines of an electron being attracted to a positive sheet look like

Answer 24

• the field lines would connect them, still being perpendicular to both surfaces
• the lines at the back would be feeding into the electron
• with all arrows pointing towards the electron