Electric fields (Year 13) Flashcards
What is electric field strength?
The electric field strength (E) at a point in a field is defined as the force per unit charge on a positive test charge placed at that point
What 2 things does an object need in order to be used as a test charge?
It should have a sufficiently small mass and charge in order for it to test the strength of a field at a given point. Any charged object placed in a field has a force exerted on it.
What is the unit of E?
N/C^-1 AKA Newton per coulomb
What is the formula for electric field strength and what can it be used to tell.?
E=F/Q.The formula can tell the magnitude of the force exerted due to the electric field on a positive test charge placed at a given point in the field.
What type of quantity is Electric field strength and what is its direction?
It is a vector quantity and the direction of the field is the same as the direction of the force on a positive test charge (field lines). If the charge is negative the force on it is in the opposite direction to the electric field.
How much charge ideally should a test mass have and why?
It should have a charge of less than 1C so that it does not interfere with the charges generating the field. It can change the electric field strength if it is greater than 1C.
Describe the field pattern between two oppositely charged conducting plates.
The field lines run from the positive plate to the negative plate, the field lines are parallel to each other and they are at right angles to the plates. The field is uniform because the lines are of equal length and are in the same direction
How do you calculate the electric field strength between two oppositely charged plates?
E=V/d Voltage provides the field/the distance between the two plates. E can be written as volt per metre.
In a uniform Electric field what is the same everywhere?
E-Electric field strength is the same everywhere.
What influences the strength of a field?
The greater the charge of the object the stronger the field, the more concentrated charge is on a surface the greater the field strength above the surface. In a metal conductor charge spreads across the surface.
Where are the field lines of a v-shaped conductor concentrated and why?
They are concentrated at the tip of the V and this is because most of the charge is concentrated there.
What does the electric field between two [plates depend on? Also what is proportional to?
It depends on the concentration of charge on the surface of the plates facing each other. The charge is spread out evenly across the surface of the plates. The electric field strength between two plates is proportional to the charge per unit area on the surface of the plates.
What is the formula for electric field strength due to charge on a plate
E*(epsilon 0)=Q/A we can add epsilon into the equation. value is 8.85x10^-12. farads per metre.Farad=1C/1V
What is Epsilon Nought?
It is the permittivity of free space, it represents the charge per unit area on a surface in a vacuum that produces an electric field of strength 1 volt per metre between the plates. Permittivity is the ability to store electrical energy in an electrical field.
What needs to be done in order to bring two objects with the same charge together? What’s the electrical potential at infinity?
Work must be done in order to bring two objects of the same charge together. As the objects are brought closer together their electric potential energies increase. At infinity, the electric potential is zero. The object has to overcome the force of repulsion from the other objects electric field in order to come close together.
What is the definition of electric potential? What is its unit?
The electric potential at a point in an electric field is defined as the work done per unit positive charge on a positive test charge to move an object from infinity to that position. Its unit is the volt. It can also be referred to as the difference in potential energy per unit charge between two positions.
What is the formula for electric potential?
This applies for a positive charge V=Ep/Q, where Ep is the electrical potential energy of a charge in that position and Q, is the charge of the object. Ep also represents work done.Ep=Q(v2-v1).
What is electrical potential energy and how is it stored?
Electrical potential energy is the work done required to move from a position of given potential to another. It is stored in the object when it moves to that position.
What are equipotentials?
They are surfaces of constant potential.No work is done on an object here so their electric potential energy remains constant. This is because the force due to the electric field lines is at 90 degrees to the surface of the equipotentials. The electric field lines meet the equipotentials at 90*.
What is the potential gradient? How does it vary in a non-uniform field?
At any position is the change in potential per unit change of distance in a given direction. In a non-unifrom field it varies with position and distance.
What is the potential gradient when a charge is moved away from a negative plate (uniform field)? What is E equal to.
When a charge is moved away from a negative plate the gradient is a positive straight line. This means that potential increases in the opposite direction to the electric field.The potential is proportional to the perpendicular distance moved. The gradient is equal to V/d for a negative charge. The gradient is constant. The electric field strength is equal to the negative of the potential gradient.
How do you calculate the potential gradient for a non-uniform field?
The gradient is equal to change in V/change in X. Where V is the difference in potential between the two points and x is the distance between them.E=-deltaV/delta x. The potential gradient is in the opposite direction to the field lines. The closer the equipotentials are the greater the potential gradient is at right angles to the equipotentials.
How are the equipotentials in a uniform field?
They are equally spaced lines parallel to the plates.
What does the force between two charged objects depend on? What is coulombs law?
The distance between them.F=1/4piE0*Q1Q2/R^2.F=force between the two charged objects. Force is proportional to the charge on each ball and 1/r^2.
