A2 - Electric Fields Flashcards
Define electric field strength
The force per unit charge on a small positive test charge at a point in a field
What is the equation for electric field strength?
E=F/Q
What happens to field lines between a flat and a pointed plate?
The lines bend towards the point, this is the most concentrated point in the field.
Is electric field strength a vector or scalar measurement?
Vector
Is electric potential a vector or scalar measurement?
Scalar
What happens to the kinetic and potential energy as a positively charged object moves away from a negatively charged one?
Its potential increases, but its kinetic decreases.
What happens to the kinetic and potential energy as a positively charged object moves away from an other positively charged one?
The potential decreases, and kinetic increases.
Where is the charge on a VdG generator/
positive charge on the belt, caused by felt removing electrons, this is transferred to the dome by a metal contact. These charges repel each other.
What happens to the potential of the VdG generator as the +ve charge moves onto the dome? Why
The potential increases as the energy per unit charge to move a +ve test charge to that point is increasing as the field is becoming stronger since the dome is more positively charged.
What is an equipotential?
A line of constant potential energy for a test charge. This runs perpendicular to the field lines.
What is the potential gradient?
Negative of the change of potential for a positive test charge ?(per unit distance)?
How is field strength calculated from potential gradient?
It is the negative of it.
What is coulomb’s law?
The force between 2 charges = Qq/4(pi)E0 * 1/r^2
Unlike gravity, what can we have when we are considering potential?
Potential hills and wells as charges can attract or repel.
What is a point charge?
A small FUCKING POSITIVE test charge that has no effect on the field in which it is placed. Theoretically useful for calculating potential etc.
When considering a charge placed in a field, what can we assume about the charge?
It is always positive
What is the ratio of distance vs total distance for two particles of charge C and 4C where the electric field strength is zero?
Use ratios to calculate:
1/3
How do you calculate the force vectors and the resultant force at a point due to two charges?
Consider the charge to be positive. Draw proportionally sized arrows attracted to negative and repelled from positive.
Use tip to tail notation to show resultant force.
What happens to the electric field lines between a plate and a pointed plate?
The field lines concentrate on the pointed plate.
What is the potential gradient?
the change in potential for a test charge per meter. Curve for a radial field, straight line for a uniform field.
What is the relationship between field strength and potential gradient?
Field strength is the negative of potential gradient.
What happens when a VdG generator is switched on?
Positive charge builds up on the belt, as electrons are removed onto the pad. Electrons transferred from the dome leave an increasing positive charge on the dome.
What is the expression for the work done moving a test charge Q from potential v1 to potential v2
w=Q(V2-V1)
In a lightening conductor, where is the field strength greatest?
Where the curve is greatest i.e. at the top. The field strength is such that it can ionise air and cause the lightning to discharge through the conductor.
What kind of motion do charged particles move in and why?
Parabolic motion as the force is always acting in one particular direction.
What is the relationship between electric potential and distance?
1/r
Is electric potential vector or scalar?
Scalar
How do you find the total electric potential for a point charge between two positive charges?
Add the electric potential due to each
What happens when an electron is moved from +ve plate to negative plate in terms of direction of force and change in electric potential?
Force towards +ve plate, EP increasing as Ek decreasing
How do you calculate work done moving an object towards a planet?
Area under field strength-distance graph
What is the shape of potential/distance graph?
-1/r
What is the shape of field strength/distance graph?
1/r^2
What direction to electric field lines point in?
Away from positive charge
