Electric Fields exam prep & answers
How does an object become charged? - correct answersWhen one uncharged material is rubbed against
another. The friction between them strips electrons off one material and onto the other. The material
that has gained electrons is now negatively charged; the other is now positively charged.
What two types of charge are there? - correct answersPositive and negative.
What do opposite charges do? - correct answersAttract.
What do like charges do? - correct answersRepel.
How can a charged object attract an uncharged object? - correct answersVia electrostatic induction.
How can matter be modelled? - correct answersMatter can be modelled as consisting of negatively
charged electrons, positively charged protons, and neutral neutrons.
What does the magnitude of charge in a proton equal? - correct answersThat of an electron.
What does the magnitude of charge in an electron equal? - correct answersThat of a proton.
What is special about the number of protons and electrons in an uncharged object? - correct
answersThey are the same.
Why is it that the electrons are involved in moving in attraction and repulsion? - correct
answersElectrons, being on the outside of atoms, are less strongly held within a material than the
protons.
What do charged objects create? - correct answersElectric fields around them.
How can we detect an electric field? - correct answersWe need to put something in it that will respond
to the field.
What are two ways of detecting an electric field? - correct answers1) Use a charged strip of gold foil
placed between charged metal plates. The foil will be attracted to the opposite charge.
2) Use grains of a material such as semolina - the material lines up in the electric field.
How can we represent electric field patterns? - correct answersBy using electric field lines.
What two things do the field lines indicate? - correct answers1) The direction of the field.
2) How strong the field is.
In which way does the electric field travel? - correct answersFrom positive to negative.
What do closely bunched lines in an electric field indicate? - correct answersA strong electric field.
, How does the strength of a uniform field act? - correct answersIt is the same at all points.
In which direction do radial fields act? - correct answersThey spread outwards in all directions.
Define electric field strength at a point. - correct answersThe electric field strength at a point is the force
per unit charge exerted on a positive charge placed at that point.
What is the equation using force and charge that describes electric field strength? - correct answersE =
F/Q
What are the units of electric field strength? - correct answersNC-1 and Vm-1.
How can you set up a uniform electric field? - correct answersYou can set up a uniform field between
two parallel metal plates by connecting them to the terminals of a power supply.
Between two parallel metal plates, what does the strength E between the plates depend upon? - correct
answersThe p.d. V between the plates and the separation d of the plates.
As EαV, and Eα1/d, what is the equation encompassing this? - correct answersE = - V/d
Why is E = - V/d negative? - correct answersV increases in the opposite direction that F acts.
As work done = energy transformed, how can we express this in terms of formulae? - correct answersFd
= VQ
How can we calculate the force F on a charge Q in a uniform field between two parallel plates? - correct
answersWe must combine the general equation for field strength E=F/Q with the equation for the
magnitude of the electric field, E=V/d.
Doing this, we get F = QE = QV/d.
If the magnitude of charge on an electron is e, what is the force experienced by the electron between
charged parallel plates? - correct answersF= eV/d.
What is the motion of an electron in a uniform electric field? - correct answersThe motion of an electron
in a uniform electric field is equivalent to a ball being thrown horizontally in the Earth's gravitational
field - a parabolic shape.
Why is the motion of an electron in a uniform electric field that of a parabolic shape? - correct
answersThe electron is repelled by the negatively charged plate and attracted by the positively charged
plate. The force on the electron is the same at all points.
Define Coulomb's law. - correct answersAny two point charges exert an electrical force on each other
that is proportional to the product of their charges and inversely proportional to the square of the
distance between them.
How does an object become charged? - correct answersWhen one uncharged material is rubbed against
another. The friction between them strips electrons off one material and onto the other. The material
that has gained electrons is now negatively charged; the other is now positively charged.
What two types of charge are there? - correct answersPositive and negative.
What do opposite charges do? - correct answersAttract.
What do like charges do? - correct answersRepel.
How can a charged object attract an uncharged object? - correct answersVia electrostatic induction.
How can matter be modelled? - correct answersMatter can be modelled as consisting of negatively
charged electrons, positively charged protons, and neutral neutrons.
What does the magnitude of charge in a proton equal? - correct answersThat of an electron.
What does the magnitude of charge in an electron equal? - correct answersThat of a proton.
What is special about the number of protons and electrons in an uncharged object? - correct
answersThey are the same.
Why is it that the electrons are involved in moving in attraction and repulsion? - correct
answersElectrons, being on the outside of atoms, are less strongly held within a material than the
protons.
What do charged objects create? - correct answersElectric fields around them.
How can we detect an electric field? - correct answersWe need to put something in it that will respond
to the field.
What are two ways of detecting an electric field? - correct answers1) Use a charged strip of gold foil
placed between charged metal plates. The foil will be attracted to the opposite charge.
2) Use grains of a material such as semolina - the material lines up in the electric field.
How can we represent electric field patterns? - correct answersBy using electric field lines.
What two things do the field lines indicate? - correct answers1) The direction of the field.
2) How strong the field is.
In which way does the electric field travel? - correct answersFrom positive to negative.
What do closely bunched lines in an electric field indicate? - correct answersA strong electric field.
, How does the strength of a uniform field act? - correct answersIt is the same at all points.
In which direction do radial fields act? - correct answersThey spread outwards in all directions.
Define electric field strength at a point. - correct answersThe electric field strength at a point is the force
per unit charge exerted on a positive charge placed at that point.
What is the equation using force and charge that describes electric field strength? - correct answersE =
F/Q
What are the units of electric field strength? - correct answersNC-1 and Vm-1.
How can you set up a uniform electric field? - correct answersYou can set up a uniform field between
two parallel metal plates by connecting them to the terminals of a power supply.
Between two parallel metal plates, what does the strength E between the plates depend upon? - correct
answersThe p.d. V between the plates and the separation d of the plates.
As EαV, and Eα1/d, what is the equation encompassing this? - correct answersE = - V/d
Why is E = - V/d negative? - correct answersV increases in the opposite direction that F acts.
As work done = energy transformed, how can we express this in terms of formulae? - correct answersFd
= VQ
How can we calculate the force F on a charge Q in a uniform field between two parallel plates? - correct
answersWe must combine the general equation for field strength E=F/Q with the equation for the
magnitude of the electric field, E=V/d.
Doing this, we get F = QE = QV/d.
If the magnitude of charge on an electron is e, what is the force experienced by the electron between
charged parallel plates? - correct answersF= eV/d.
What is the motion of an electron in a uniform electric field? - correct answersThe motion of an electron
in a uniform electric field is equivalent to a ball being thrown horizontally in the Earth's gravitational
field - a parabolic shape.
Why is the motion of an electron in a uniform electric field that of a parabolic shape? - correct
answersThe electron is repelled by the negatively charged plate and attracted by the positively charged
plate. The force on the electron is the same at all points.
Define Coulomb's law. - correct answersAny two point charges exert an electrical force on each other
that is proportional to the product of their charges and inversely proportional to the square of the
distance between them.
