Topic 7: Electric and Magnetic Fields Flashcards
(27 cards)
What is a force field?
A region of space in which objects will experience a non-contact force.
What causes the generation of fields?
Objects with mass or charge
Fill in the blanks:
Any object experiencing a force in a field will enact an ________________________ on the body generating the field.
Any object experiencing a force in a field will enact an equal and opposite force on the body generating the field.
Define:
Radial Field.
A field directed radially towards or away from the body generating it.
How does the strength of the field affect the square of the distance from the centre in a radial field?
The strength of the field is inversely proportional to the sqaure of the distance from its centre.
Define:
Uniform Field.
A field of strength in a single, uniform direction.
State the use of vector arrows in field lines.
To represent the direction and strength of a force field.
What direction do vector arrows point towards?
They point in the direction of the force that a body would experience at that point in the field.
What does the relative distance between field lines indicate?
The strength of the field.
Closer field lines means a stronger field.
Fill in the blanks:
Field lines for a uniform field are ____________ and ____________ while those for a radial are ____________________________.
Field lines for a uniform field are parallel and equidistant while those for a radial are all directed at a central point.
Define:
Electric Field, E.
A force field generated due due to charge, which will enact an attractve or repulsive force on other charges that enter it.
What unit measures charge, and what signs can be given to it?
The Coulomb, C, is the SI unit of charge and can have values that are positive (for current or protons) or negative (for electrons).
What are the rules for attraction of charges?
Opposite charges (+,-) are attracted towards each other.
The force of attraction varies proportionally with magnitude of charges.
What are the rules for repulsion of charges?
Like charges (+,+ or -,-) are repulsed away from each other.
The force of repulsion varies proportionally with magnitude of charges.
What do electric field lines show?
The direction a small positive charge would move.
What type of electric field to point charges generate?
Point charges generate radial electrric fields.
A spherical charge can be treated as an equivalent point charge at its centre.
What law determines the magnitude of the electric force between two charges?
Coulomb’s Law
Define:
Coulomb’s Law.
The magnitude of the electrostatic force between two point charges is proportionl to the product of those charges and inversely proportional to the square of the distance between them.
Give Coulomb’s law in equation form.
Coulomb’s Law, defined as:
F = (Q₁Q₂)/(4πε₀r²)
Where;
⦁Q₁Q₂ = charges of the two point charges in Coulombs (C)
⦁ F = Electrostatic force between the two point charges in Newtons (N)
⦁ ε₀ = Permittivity of free space = 8.85 × 10⁻¹² Fm⁻¹
⦁ r = distance between the charges in m
What does permittivity depend on?
The medium the fied is in.
State the assumption about permittivity of air.
The permittivity of air can be assumed to be same as that of a vacuum,ε₀.
Give Coulomb’s law in equation form involving Coulomb’s Constant.
F = (kQ₁Q₂)/(r²)
When;
k = 1/(4πε₀)
=8.99 × 10⁹ Nm²/C²
Where;
⦁Q₁Q₂ = charges of the two point charges in Coulombs (C)
⦁ F = Electrostatic force between the two point charges in Newtons (N)
⦁ ε₀ = Permittivity of free space = 8.85 × 10⁻¹² Fm⁻¹
⦁ r = distance between the charges in m
Better to use the constant version because it’s less time consuming.
Fill in the blanks:
Attractive forces will be ____________ while repulsive forces will be ____________.
Attractive forces will be negative while repulsive forces will be positive.
What will be the change in force, if two positive charges separated by a distance r are now moved to a distance 2r apart?
The charges will now experience 1/4 original force.
From: F = kQ₁Q₂/r² the force is inversely proportional to the square of distance. Doubling distance will reduce magnitude of force to ¼ its original value.
