Electric Fields

Question 1

What do all charged particles produce around them?

Answer 1

An electric field that exerts a force on any other charged particle within range.

Question 2

What does Coulomb’s Law define?

Answer 2

The electrostatic force between two point charges.

Question 3

What is the form of Coulomb’s Law?

Answer 3

The electrostatic force is proportional to the product of the charges and inversely proportional to the square of their separation.

Question 4

State the Coulomb’s Law equation.

Answer 4

FE = (1 / (4πε0)) * (Q1Q2 / r²)

Question 5

Define FE in Coulomb’s Law and give its unit.

Answer 5

FE = electrostatic force between two charges (N)

Question 6

Define Q1 and Q2 in Coulomb’s Law and give their unit.

Answer 6

Q1 and Q2 = two point charges (Coulombs, C)

Question 7

Define r in Coulomb’s Law and give its unit.

Answer 7

r = distance between the centre of the charges (metres, m)

Question 8

Define ε0 and its significance.

Answer 8

ε0 = permittivity of free space; it shows the capability of a vacuum to permit electric fields.

Question 9

What is the inverse square law in Coulomb’s Law?

Answer 9

The force is inversely proportional to the square of the distance between charges.

Question 10

What does a negative electrostatic force imply?

Answer 10

It is an attractive force (between opposite charges).

Question 11

What does a positive electrostatic force imply?

Answer 11

It is a repulsive force (between like charges).

Question 12

When can uniformly charged spheres be treated as point charges?

Answer 12

When the separation is measured from the center of both spheres.

Question 13

What approximation is made about air in electrostatics calculations?

Answer 13

Air is treated as a vacuum, allowing the use of ε0.

Question 14

What is the nature of the electric field lines around a spherical conductor?

Answer 14

They are radial, identical to those of a point charge.

Question 15

What direction do electric field lines point for a positive spherical conductor?

Answer 15

Away from the center.

Question 16

What direction do electric field lines point for a negative spherical conductor?

Answer 16

Towards the center.

Question 17

Draw and explain the electric field lines between two point charges.

Answer 17

It is provided in the document.

Question 18

What is the direction of electric field lines in general?

Answer 18

From positive to negative charge.

Question 19

What does a radial field imply?

Answer 19

Field lines spread uniformly in all directions.

Question 20

What is a uniform electric field?

Answer 20

A field with the same electric field strength throughout, represented by equally spaced field lines.

Question 21

What does the spacing of electric field lines indicate?

Answer 21

Closer lines indicate a stronger field, wider lines indicate a weaker field.

Question 22

Define electric field strength and give its formula.

Answer 22

E = F / Q, where E is electric field strength (N/C), F is force (N), Q is charge (C)

Question 23

Why is a positive test charge used in defining electric field strength?

Answer 23

To determine the direction of the electric field.

Question 24

What is the direction of electric field strength vector?

Answer 24

Away from a positive charge, towards a negative charge.

Question 25

State the formula for electric field strength between parallel plates.

Answer 25

E = V / d

Question 26

Define V and d in the context of electric fields.

Answer 26

V = potential difference (volts), d = distance between plates (metres)

Question 27

What does the equation E = V/d show about electric fields?

Answer 27

Greater voltage means stronger field; greater separation means weaker field.

Question 28

When can E = V/d not be used?

Answer 28

It cannot be used for point charges; it is only valid for uniform fields.

Question 29

Define work done in moving a charge in an electric field.

Answer 29

W = Fd = ΔVQ

Question 30

Define the motion of a charged particle in a uniform electric field.

Answer 30

It moves in a parabolic trajectory if entering perpendicularly.

Question 31

What determines the direction of deflection of a charged particle in a field?

Answer 31

Its charge; positive goes to the negative plate and vice versa.

Question 32

How does mass affect deflection in an electric field?

Answer 32

Greater mass means less deflection.

Question 33

How does charge magnitude affect deflection in an electric field?

Answer 33

Greater charge means more deflection.

Question 34

How does particle speed affect deflection in an electric field?

Answer 34

Greater speed means less deflection.

Question 35

What is the electric field strength of a point charge?

Answer 35

E = (1 / (4πε0)) * (Q / r²)

Question 36

Define Q and r in the point charge field equation.

Answer 36

Q = point charge (C), r = distance from charge (m)

Question 37

What is the relationship between E and r in a radial field?

Answer 37

E ∝ 1 / r²

Question 38

What is the direction of electric field strength vector for positive charge?

Answer 38

Away from the charge.

Question 39

What is the direction of electric field strength vector for negative charge?

Answer 39

Towards the charge.

Question 40

List a key similarity between electric and gravitational fields.

Answer 40

Both follow inverse square laws.

Question 41

What is a unique feature of gravitational vs. electrostatic forces?

Answer 41

Gravitational forces are always attractive; electrostatic can be attractive or repulsive.

Question 42

How do gravitational and electric field lines compare?

Answer 42

Field lines around point mass and negative charge are identical.

Question 43

How do potentials compare between gravity and electrostatics?

Answer 43

Gravitational potential is always negative; electric potential can be positive or negative.

Question 44

What must be done to move a positive charge closer to another positive charge?

Answer 44

Work must be done to overcome the force of repulsion.

Question 45

What must be done to move a positive charge away from a negative charge?

Answer 45

Work must be done to overcome the force of attraction.

Question 46

What happens to the energy of a charge when it is pushed upon?

Answer 46

Energy is transferred to the charge, increasing its potential energy.

Question 47

What happens to the potential energy of a free positive charge near a repelling charge?

Answer 47

It decreases back to 0 as the charge moves away.

Question 48

What is electric potential defined as?

Answer 48

The work done per unit positive charge in bringing a point test charge from infinity to a defined point.

Question 49

Is electric potential a scalar or vector quantity?

Answer 49

It is a scalar quantity.

Question 50

Why can electric potential have a positive or negative sign?

Answer 50

Because it is positive around a positive charge and negative around a negative charge.

Question 51

What is the electric potential at infinity?

Answer 51

Zero.

Question 52

What happens to electric potential when a positive test charge moves closer to a negative charge?

Answer 52

The electric potential decreases.

Question 53

What happens to electric potential when a positive test charge moves closer to a positive charge?

Answer 53

The electric potential increases.

Question 54

How do you find the potential at a point caused by multiple charges?

Answer 54

By summing the potential from each charge.

Question 55

In which direction does electric potential V decrease?

Answer 55

In the direction the test charge would naturally move.

Question 56

What causes electric potential difference between two points?

Answer 56

Different distances from a charge cause different electric potentials.

Question 57

What is the equation for electric potential difference ΔV?

Answer 57

ΔV = Vf – Vi.

Question 58

What does a difference in electric potential cause?

Answer 58

A difference in electric potential energy.

Question 59

What is the equation for electric potential in a radial field?

Answer 59

V = Q / (4πε₀r)

Question 60

What does the electric potential do for a positive charge as r decreases?

Answer 60

It increases.

Question 61

What does the electric potential do for a negative charge as r decreases?

Answer 61

It decreases.

Question 62

How does electric potential change with distance?

Answer 62

It changes according to an inverse square law.

Question 63

What is the electric potential equation still valid for?

Answer 63

A conducting sphere, using point charge approximation.

Question 64

What should you do when asked to draw and explain electric potential graphs?

Answer 64

Draw and explain the graph. The answer is provided in the document.

Question 65

What is the relation between E, ΔV, and Δr?

Answer 65

E = ΔV / Δr.

Question 66

How is electric field related to electric potential on a graph?

Answer 66

The electric field is the gradient of the potential-distance graph.

Question 67

What happens to electric potential around a positive charge?

Answer 67

It decreases with distance.

Question 68

What happens to electric potential around a negative charge?

Answer 68

It increases with distance.

Question 69

What relation does V vs r follow for positive charge?

Answer 69

1/r.

Question 70

What relation does V vs r follow for negative charge?

Answer 70

-1/r.

Question 71

What relation does E vs r follow?

Answer 71

1/r² (inverse square law).

Question 72

What does the area under an E vs r graph represent?

Answer 72

Change in electric potential ΔV.

Question 73

What is the equation for work done on a charge?

Answer 73

ΔW = qΔV.

Question 74

What is the equation for change in EPE when moving a charge in a radial field?

Answer 74

ΔW = Qq(1/r1 - 1/r2) / (4πε₀)

Question 75

When is work done on a charge?

Answer 75

When moving it away from another charge.

Question 76

What are equipotential lines?

Answer 76

Lines joining points with the same electric potential.

Question 77

What is the orientation of equipotential lines with respect to electric field lines?

Answer 77

They are always perpendicular.

Question 78

What is ΔV when moving along an equipotential line?

Answer 78

ΔV = 0.

Question 79

What is the energy change when moving along an equipotential?

Answer 79

There is no energy change.