Electric Fields Flashcards
What do all charged particles produce around them?
An electric field that exerts a force on any other charged particle within range.
What does Coulomb’s Law define?
The electrostatic force between two point charges.
What is the form of Coulomb’s Law?
The electrostatic force is proportional to the product of the charges and inversely proportional to the square of their separation.
State the Coulomb’s Law equation.
FE = (1 / (4πε0)) * (Q1Q2 / r²)
Define FE in Coulomb’s Law and give its unit.
FE = electrostatic force between two charges (N)
Define Q1 and Q2 in Coulomb’s Law and give their unit.
Q1 and Q2 = two point charges (Coulombs, C)
Define r in Coulomb’s Law and give its unit.
r = distance between the centre of the charges (metres, m)
Define ε0 and its significance.
ε0 = permittivity of free space; it shows the capability of a vacuum to permit electric fields.
What is the inverse square law in Coulomb’s Law?
The force is inversely proportional to the square of the distance between charges.
What does a negative electrostatic force imply?
It is an attractive force (between opposite charges).
What does a positive electrostatic force imply?
It is a repulsive force (between like charges).
When can uniformly charged spheres be treated as point charges?
When the separation is measured from the center of both spheres.
What approximation is made about air in electrostatics calculations?
Air is treated as a vacuum, allowing the use of ε0.
What is the nature of the electric field lines around a spherical conductor?
They are radial, identical to those of a point charge.
What direction do electric field lines point for a positive spherical conductor?
Away from the center.
What direction do electric field lines point for a negative spherical conductor?
Towards the center.
Draw and explain the electric field lines between two point charges.
It is provided in the document.
What is the direction of electric field lines in general?
From positive to negative charge.
What does a radial field imply?
Field lines spread uniformly in all directions.
What is a uniform electric field?
A field with the same electric field strength throughout, represented by equally spaced field lines.
What does the spacing of electric field lines indicate?
Closer lines indicate a stronger field, wider lines indicate a weaker field.
Define electric field strength and give its formula.
E = F / Q, where E is electric field strength (N/C), F is force (N), Q is charge (C)
Why is a positive test charge used in defining electric field strength?
To determine the direction of the electric field.
What is the direction of electric field strength vector?
Away from a positive charge, towards a negative charge.
State the formula for electric field strength between parallel plates.
E = V / d
Define V and d in the context of electric fields.
V = potential difference (volts), d = distance between plates (metres)
What does the equation E = V/d show about electric fields?
Greater voltage means stronger field; greater separation means weaker field.
When can E = V/d not be used?
It cannot be used for point charges; it is only valid for uniform fields.
Define work done in moving a charge in an electric field.
W = Fd = ΔVQ
Define the motion of a charged particle in a uniform electric field.
It moves in a parabolic trajectory if entering perpendicularly.
What determines the direction of deflection of a charged particle in a field?
Its charge; positive goes to the negative plate and vice versa.
How does mass affect deflection in an electric field?
Greater mass means less deflection.
How does charge magnitude affect deflection in an electric field?
Greater charge means more deflection.
How does particle speed affect deflection in an electric field?
Greater speed means less deflection.
What is the electric field strength of a point charge?
E = (1 / (4πε0)) * (Q / r²)
Define Q and r in the point charge field equation.
Q = point charge (C), r = distance from charge (m)
What is the relationship between E and r in a radial field?
E ∝ 1 / r²
What is the direction of electric field strength vector for positive charge?
Away from the charge.
What is the direction of electric field strength vector for negative charge?
Towards the charge.
List a key similarity between electric and gravitational fields.
Both follow inverse square laws.
What is a unique feature of gravitational vs. electrostatic forces?
Gravitational forces are always attractive; electrostatic can be attractive or repulsive.
How do gravitational and electric field lines compare?
Field lines around point mass and negative charge are identical.
How do potentials compare between gravity and electrostatics?
Gravitational potential is always negative; electric potential can be positive or negative.
What must be done to move a positive charge closer to another positive charge?
Work must be done to overcome the force of repulsion.
What must be done to move a positive charge away from a negative charge?
Work must be done to overcome the force of attraction.
What happens to the energy of a charge when it is pushed upon?
Energy is transferred to the charge, increasing its potential energy.
What happens to the potential energy of a free positive charge near a repelling charge?
It decreases back to 0 as the charge moves away.
What is electric potential defined as?
The work done per unit positive charge in bringing a point test charge from infinity to a defined point.
Is electric potential a scalar or vector quantity?
It is a scalar quantity.
Why can electric potential have a positive or negative sign?
Because it is positive around a positive charge and negative around a negative charge.
What is the electric potential at infinity?
Zero.
What happens to electric potential when a positive test charge moves closer to a negative charge?
The electric potential decreases.
What happens to electric potential when a positive test charge moves closer to a positive charge?
The electric potential increases.
How do you find the potential at a point caused by multiple charges?
By summing the potential from each charge.
In which direction does electric potential V decrease?
In the direction the test charge would naturally move.
What causes electric potential difference between two points?
Different distances from a charge cause different electric potentials.
What is the equation for electric potential difference ΔV?
ΔV = Vf – Vi.
What does a difference in electric potential cause?
A difference in electric potential energy.
What is the equation for electric potential in a radial field?
V = Q / (4πε₀r)
What does the electric potential do for a positive charge as r decreases?
It increases.
What does the electric potential do for a negative charge as r decreases?
It decreases.
How does electric potential change with distance?
It changes according to an inverse square law.
What is the electric potential equation still valid for?
A conducting sphere, using point charge approximation.
What should you do when asked to draw and explain electric potential graphs?
Draw and explain the graph. The answer is provided in the document.
What is the relation between E, ΔV, and Δr?
E = ΔV / Δr.
How is electric field related to electric potential on a graph?
The electric field is the gradient of the potential-distance graph.
What happens to electric potential around a positive charge?
It decreases with distance.
What happens to electric potential around a negative charge?
It increases with distance.
What relation does V vs r follow for positive charge?
1/r.
What relation does V vs r follow for negative charge?
-1/r.
What relation does E vs r follow?
1/r² (inverse square law).
What does the area under an E vs r graph represent?
Change in electric potential ΔV.
What is the equation for work done on a charge?
ΔW = qΔV.
What is the equation for change in EPE when moving a charge in a radial field?
ΔW = Qq(1/r1 - 1/r2) / (4πε₀)
When is work done on a charge?
When moving it away from another charge.
What are equipotential lines?
Lines joining points with the same electric potential.
What is the orientation of equipotential lines with respect to electric field lines?
They are always perpendicular.
What is ΔV when moving along an equipotential line?
ΔV = 0.
What is the energy change when moving along an equipotential?
There is no energy change.
