Electric Fields COPY Flashcards
Define Coulombs Law
The force acting between two charged bodies is inversely proportional to the square of the distance between them and is directly proportional to the product of the two charges.
If the distance between the charge doubles, what happens to the magnitude of the force?
X 1/4
If the distance between the charge triples, what happens to the magnitude of the force?
X 1/9
If the distance between the charge halves, what happens to the magnitude of the force?
X 4
Define electric field
The region of space where a charged particle feels a force
What is the equation for the strength of an electric field?
E = F/Q
What is the units for electric field strength?
N/C, V/m
Define electric field strength
The force per unit positive charge
What is the direction of an electric field at a point equal to?
The direction of the force at that point
Is electric field strength a scalar or vector quantity?
Vector
How does the density of an electric field line relate to its strength?
The density of the field lines is a measure of the strength of an electric field
Where does charge appear to act on a charged sphere?
Charge is considered to act from the centre
Which way do the arrows face on a field lines diagram depicting an positive charge in the centre?
Away from the positive centre
Which way do the arrows face on a field lines diagram depicting an negative charge in the centre?
Towards the negative centre
Explain what will happen to a positive particle if it is moving in the same direction as the field
The particle will get a force on it in the same direction and will accelerate. EQ= ma
Explain what will happen to a positive particle if it is moving in the opposite direction as the field
Force is in the opposite direction to its motion. There is a negative acceleration so the particle will slow down
Explain what will happen to an electron if it is moving at right angles to the field
- An e- will feel a force on it in the opposite direction to the E field because it is -ve
- The horizontal component of the e- velocity will be constant
- The force on it causes it to accelerate in the vertical direction
What can be used to determine the acceleration in the vertical direction of an e- in an E field at right angle to its direction of motion
SUVAT equations
What is meant by a uniform field?
The force on a charge will be the same wherever the charge is between the plates
How do you calculate field strength between parallel plates?
E = V/d
Define electric potential
The electric potential at a point is defined as the work done taking a unit positive charge from infinity to that point
Is electric potential a scalar or vector quantity
Scalar
What is the potential around a positive charge?
Positive as work needs to be done. This is due the repulsive force
What is the potential around a negative charge?
Negative since the charge itself will do work to pull the charge from infinity towards itself
What is an equipotential?
Points of equal potential at right angles to the electric field lines
What work is done moving alone an equipotential?
No work is done
What is done moving from one potential to the other?
Work is done. The +ve or -ve sign relates to the direction of energy transfer
Is work done moving along an equipotential?
No
Is work done moving along field lines?
Yes
The work done taking a charge through a potential difference /\V is defined as:
W = Q /\V
Define electrical potential energy
The work done in taking the charge from infinity to that point
What does the force act on in a gravitational field?
Mass
What does the force act on in a electric field?
A charged particle
What is the direction of the force in a gravitational field?
Attractive
What is the direction of force in an electric field?
Attractive/ Repulsive
How do you calculate the field strength for a gravitational field?
g = F/m
How do you calculate the field strength for an electric field?
E = F/q
What is the direction of the gravitational field around an isolated object?
Towards object
What is the direction of the electric field around an isolated object?
Towards -ve Away from +ve
What is the definition of electrical potential?
The work done in taking unit positive charge from infinity to that point.
Describe Milikan’s oil drop experiment
- A charged oil drop was suspended using an electric field which opposes the weight - The charge (q) varied but was always a multiple of e
What is the formula for Coulombs Law?
Draw a diagram for the fields between two positive charges.
Draw a diagram for the fields between a positive and negitive charge.
Draw the path of an electron moving at right angles to the electric field.
Draw the field lines for a uniform field inbetween positive and negitive plates.
The electric field strength between a pair of plates 4.0cm in length in a cathode ray tube has a value of 23000N/C. An electron enters the field at right angles at a velocity of 3.7x10^7 m/s from left to right. What is the velocity and direction of the electron as it leaves the field?
What is the equation that defines field strength?
What does the E against r graph for a point charge in a radial field look like?
What does the E against r graph for a hollow sphere of charge in a radial field look like?
What does the graph of V against r graph for a radial field look like?
What is the forlula for the potential, V, at a distance r form a charge Q given by?
What is the equation for the potential gradient?
There are two plates with a 9V potential difference. Draw in the 3V and 6V equipotential.
What graph can be used to find the change in potential?
Graph of field strength against r
Draw the graph of E against r for a uniform field.
How do you work out the change in potential for a uniform field using an E against r graph?
Area under the graph
How do you work out the change in potential for a radial field using an E against r graph?
Area under the graph
What does the graph of E against r look like for a radial field?
What is the derivation for E=V/d from WD moving between parallel plates?
What is the formula for electric potential energy?
Suppose Q1 had a charge of +5C and Q2 has a charge of -3.0C, if they are 0.200m apart what is the field strength in the middle of them?
Suppose Q1 had a charge of +2 microC and Q2 had a charge of +3 microC, if they are 5mm apart what is the potential difference 2mm from the 2 microC charge?
Suppose Q1 had a charge of -30 microC and Q2 had a charge of +50 microC, if they are 10mm apart what is the potential difference 2mm from the -30 microC charge?
What is the graph for Coulombs Law (including values for R, 2R, 3R & 4R) when the initial force is 12. What is the area under the graph equal to?
What is the graph for Electric field strength (including values for R, 2R, 3R & 4R) when the initial E value is 12. What is the area under the graph equal to?
What is the graph for potential (including values for R, 2R, 3R & 4R) when the initial potential is 12. What is the gradient equal to?
Compare the equations for the force law between two objects for gravitational and electric fields.
Compare the equations for the potential a distance r from an object if field is radial for gravitational and electric fields.
Compare the equations that show how the field strength and potential are related for gravitational and electric fields.
Compare the equations for the potential energy of mass/charged particle a distance r from an object if the field is radial for gravitational and electric fields.
Compare the equations for the change in potential evergy of mass/charge for gravitational and electric fields.
