electric fields Flashcards
what does any object with charge have, and what does this charge allow them to do?
EF
any object with charge has an electric field around it - a region where it can attract or repel other charges
what is electric charge (Q) measured in?
EF
electric charge (Q) is measured in Coulombs (C)
can electric charges be positive or negative?
EF
yes
what do oppositely charged particles do to each other?
EF
oppositely charge particles attract each other
what do like charged particles do to each other?
EF
like charges repel each other
what does a charged object experience if placed in an electric field?
EF
if a charged object is placed in an electric field, the charged object will experience a force
how does a charged object act, if it is a sphere with evenly distributed charge? and what does this mean?
EF
⋅ if a charged object is a sphere, with evenly distributed charge (spherically symmetrical), it will act as if all of its charge is at its centre
⋅ so you can model it as a point charge (at distances larger than its radius)
how large does a distance have to be, to model a charged object as a point charge?
EF
you can model a charged object as a point charge, as long as the distances are larger than the charged object’s radius
how are electric fields represented on a field diagram?
EF
just like with gravitational fields, electric fields can be represented by field lines
what do you use coulomb’s law to work out?
EF
you need coulomb’s law to work out F electric
what is F electric?
EF
F electric is the force of attraction or repulsion between two point charges (or two objects that behave as point charges)
what does it mean if F electric is negative?
EF
⋅ if F electric is negative, this means that the force is attractive
⋅ this is bc the charges (Q and q) must be opposite for F electric to be negative
[⋅ bc F = kQq/(r^2)
⋅ when there are opposite charges (eg, a proton and an electron) that attract each other, one will be positive (the proton or positively charged ion) and one will be negative (the electron or negatively charged ion)
⋅ so when you multiply Q by q, you will be multiplying a positive with a negative
⋅ so you will end up with a negative force]
what does it mean if F electric is positive?
EF
⋅ if F electric is positive, the force between the charges is repulsive
⋅ this is bc charges (Q and q) must be like for F electric to be positive
[⋅ bc F = kQq/(r^2)
⋅ when there are like charges (eg, a proton and a proton) that repel each other, one will be one charge (eg, a proton or positively charged ion) and the other will be the same charge (another proton or positively charged ion)
⋅ so when you multiply Q by q, you will be multiplying a positive with another positive (or a negative with another negative)
⋅ so you will always end up with a positive force]
what is coulomb’s law?
EF
coulomb’s law is:
what is the relationship between the forces on Q and q?
EF
the force on q is always equal and opposite to the force on Q
what kind of law is coulomb’s law an example of, and why?
EF
⋅ coulomb’s law is an example of the inverse square law
⋅ bc the further apart the charges are, the weaker the force between the charges
what does k stand for in coulomb’s law?
EF
⋅ k is the electric force constant (or Coulomb’s law’s constant of proportionality)
⋅ k is equal to about 9.0 x10^9 N m^2 C^-2
⋅ you’ll be given k’s value in the exam, either in the data and the formula booklet, or in the question
what is electric field strength?
EF
electric field strength is defined as the force exerted[/acting] per unit positive charge
what is another way of describing electric field strength?
EF
electric field strength is the force that a charge of +1 C would experience if it was placed in an electric field
what is the equation to work out the electric field strength (E electric) (using F and q)?
EF
what does E electric also represent?
EF
E electric is also a vector pointing in the direction that a positive charge would move
what are the units for electric field strength?
EF
the units for electric field strength are N C^-1
what does the electric field strength depend on?
EF
the electric field strength often depends on where you are in the electric field
what type of field does a point charge have?
EF
a point charge (or any body that behaves as if all of its charge is concentrated at its centre) has a radial field