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Flashcards in Electricity Deck (30)
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1
Q

What happens in interactions among elementary particles?

A
  • equal quantities of positive and negative charge are produced or destroyed
  • the net charge of the universe is unchanged
  • i.e. electric charge is conserved
2
Q

What is the SI unit of electric charge?

A

the Coulomb

3
Q

Coulomb’s Law

A

F = (kq1q2)/r^2

F = magnitude of the electric force exerted by charge q1 on another charge q2 when the charges are separated by a distance r

4
Q

Coulomb’s Constant

A

k = 8.99 x 10^9 Nm^2/C^2 = 1/4pie0

5
Q

Two small spheres attract one another electrostatically. Which of the following statements is true?

a) at least one sphere must be charged
b) neither sphere needs to be charged
c) both charges must be charged and the charges must have the same sign
d) both spheres must be charged and the charges must have opposite signs

A

a) a single charge object can cause the other object to become charged, so that there is an electrostatic force between the two objects

6
Q

Electric Field

Equation

A

E = (k*q1)/r^2
Electric field, E, at a point P which is a distance from a point charge q1
Also, F=Eq -> E = F/q

7
Q

Electric Field Definition

A

E is the force on a charge divided by the magnitude of that charge, i.e. the force per unit charge E = F/q

8
Q

Finding Total Electric Field

A

Can be found by measuring the force on a small charge and dividing by q
E = lim(q->0) F / q
You have to take the limit of small q so that the test charge does not disturb the electric field of q with its own electric field

9
Q

Electric Potential Energy

Definition

A

the change in potential energy of a charge in an electric field when it is displaced a certain distance

10
Q

Electric Potential Energy

Equation

A

dU = -qEdl

11
Q

Potential Difference

Definition

A

Change in potential energy per unit charge

12
Q

Potential Difference

Equation

A

dV = dU/q = -Edl

13
Q

Change in Potential Difference

Equation

A

ΔV = Vb-Va = -∫Edl (between b and a)

14
Q

Potential at a distance R from a point charge q

A

ΔV = kq/R

using V = 0 at r = ∞ in the integral

15
Q

Electrostatic Energy of Two Point Charges, q1 and q2

A

U = (kq1q2)/r12

16
Q

Electrostatic Energy of Three Point Charges, q1, q2, q3

A

U = (kq1q2)/r12 + (kq1q3)/r13 + (kq2q3)/r23

17
Q

Electrostatic Energy - Continuous Charges

A

U = (Q,0)∫ V(q) dq

Eneryg , U, required to add a charge element dq in the presence of a potential V(q) generated by a charge distribution q

18
Q

Capacitance

Equation

A

C = Q / V = d / εA

19
Q

Capacitance

Definition

A

a measure of the capacity to store a charge, Q, for a given potential difference V

20
Q

Self Capacitance of a Spherical Conductor

A

C = 4πε0R

21
Q

Unit of Capacitance

A

1 Farad = 1 Coulomb / 1 Volt

22
Q

Permitivity of Free Space

A

ε0 = 8.85 x 10^(-12) F/m

23
Q

Surface Charge Density

A

σ = Q / A

24
Q

Electric Field Between Two Parallel Plates

A

E = V/d = σ/ε

25
Q

Electric Energy Stored in a Capacitor

Equation

A

U = (1/2)*Q²/C = (1/2)QV

= (1/2)CV²

26
Q

What is electrostatic field energy?

A

The energy required to charge a capacitor can also be thought of as the energy required to establish the electric field, the electrostatic field energy

27
Q

Electrostatic Field Energy

Equation

A

U = (1/2)εE²(Ad)

28
Q

Electric Field Energy Density

Definition

A

energy stored in the electric field per unit volume

29
Q

Electric Field Energy Density

Equation

A

u = (1/2)εE²

30
Q

Capacitance of a Cylindrical Capacitor

A

C = 2πεL / ln(R1/R2)