Electric Fields Flashcards
How do charges interact in these situations?
- Like charges repel
- Opposite charges attract
Which direction will these charges move?
Electric field lines shows direction of Force on +ve charges
(-ve charges are opposite)
How are radial and uniform electric fields different?
- Radial fields have a varying field strength (weaker when further apart)
- Uniform fields have a constant field strength
For electric fields, how are are equipotentials related to the field lines?
Equipotentials always perpendicular to field lines
How can you change this situation to increase the force on the charge?
- Increase field strength
- Increase magnitude of charge
What field lines are produced by…
a) +ve charge
b) -ve charge
Field lines always act…
- Away from +ve
- Towards -ve
How do the field lines look for these two interacting oppositely charged particles?
How do the field lines look for these two interacting like charged particles?
NOTE: Field lines never cross
What is the electric field strength at the following points?
Field strength is constant between parallel plates (capacitor)
E1 = E2 = E3
What is the electric potential at the following points?
Electric potential linearly increases between parallel plates (capacitor)
Define Coulomb’s Law
Define electric field strength
Force per unit charge acting on a small positive charge
What force would act on a 5C charge placed at 6NC-1?
F=Eq → 5x6 = 30N
What is wrong here?
Electric field strength ≠ acceleration
How do you calculate electric field strength outside a conducting sphere?
Treat it as a point charge
How do you calculate electric field strength inside a conducting sphere?
E=0 everywhere!!!
Fres= 0 , change in Ep = 0 , change in V = 0
What is the graph of electric field strength for a conducting sphere?
How is electric field strength calculated here?
For parallel plates calculate E first if possible
How do you work out the resultant field strength between charges?
- Work out field strength from each
- Label vectors
- Add or subtract field strengths
Can you use SUVATs here?
Yes!
Field strength constant → Acceleration constant
Why is potential energy here +ve?
Ep = 0 at ∞
Increases as charge moves closer
Why is potential energy here +ve?
Ep = 0 at ∞
Increases as charge moves closer
Why is potential energy here -ve?
Ep = 0 at ∞
Decreases as charge moves closer
Why is potential energy here -ve?
Ep = 0 at ∞
Decreases as charge moves closer
Define electric potential and what is its equation?
Work done per coulomb moving positive charge from infinity to that point
(¼πε0) * (Q/r)
Why does the moving charge’s potential energy increase?
Equipotentials show the change in potential of a +ve charge
If +ve charge → decreases
If -ve charge → increases
How are these charges different?
Q is the charge creating the field
q is the charge moving in the field
What is wrong here?
Electric potential is scalar
But they are opposite → must be subtracted
How do you calculate the neutral electric field strength (or force) point between charges?
How do you calculate the neutral electric potential point between charges?
What is the graph of electric force for a conducting sphere?
Same as field strength graph
What is the graph of electric potential for a positively charged conducting sphere?
The gradient of the graph at a point = |E|.
The Ep - r graph for like charges is the same and the gradient at a point is |F|
What is the graph of electric potential for a negatively charged conducting sphere?
The gradient of the graph at a point = |E|.
The Ep - r graph for opposite charges is the same and the gradient at a point is |F|
What two situations produce a uniform electric field?
- Radial field over a short distance
- Field between 2 parallel plates
