3.7.3 Electric fields

Question 1

What kind of object experiences an electric field?

Answer 1

Static or moved charged particles

Question 2

What is Coulomb’s law?

Answer 2

The electrostatic force between two point charges is directly proportional to the product of the charges and inversely proportional to the distance squared between them

Question 3

What is Coulomb’s law as an equation?

Answer 3

F_E= Q_1Q_2/4πε_0r^2

Question 4

Approximations for Coulomb’s law:

Answer 4

Air is treated as a vacuum, so permittivity of free space is used.
A uniform spherical conductor is assumed to have evenly distributed charge.

Question 5

What is electric field strength?

Answer 5

The electrostatic force per unit positive charge acting on the charge at that point

Question 6

What is the formula for electric field strength for a uniform field?

Answer 6

E=F/Q=V/d(this one is not used for a point charge)

Question 7

How is the electric field strength between 2 plates equation derived?

Answer 7

E=F/Q
W=Fd
hence E=(W/d/Q)=V/d

Question 8

What affects the amount of deflection a charge in an electric field experiences?

Answer 8

Mass - greater mass= smaller deflection
Charge - greater charge = greater deflection
Speed - greater speed = smaller deflection

Question 9

What is a motion of a charged particle in an electric field?

Answer 9

Parabolic (if motion perpendicular to lines)

Question 10

What is the formula for the electric field of a point charge?

Answer 10

E=Q/4πε_0r^2

Question 11

What is electric potential?

Answer 11

The work done per unit positive charge in bringing a point test charge from infinity to a defined point. When a positive test charge is moved closer to a negative charge, its electric potential decreases. If its moved closer to a positive charge, it increases.

Question 12

What is the formula for the electric potential due to a point charge?

Answer 12

V=Q/4πε_0r

Question 13

What does the V-r graph look like?

Answer 13

1/(x^2) graph

Question 14

What is the electric field at a point from a graph?

Answer 14

gradient of V-d graph

Question 15

What is the potential gradient?

Answer 15

The rate of change of electric potential with respect to displacement in the direction of the field

Question 16

What is the formula for work done on a charge?

Answer 16

deltaW=qdeltaV

Question 17

What is the formula for change in work done on a charge?

Answer 17

delta EPE = Qq/(4πε_0r) (1/r_2 - 1/r_1)

Question 18

What are the properties of equipotential lines for electric fields?

Answer 18

They are dotted
For uniform field they are horizontal straight lines that are parallel and equally spaced.
For radial field they are concentric circles and become further away.
No work is done along a line of equipotential.