Term
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Definition
The electric field strength - E - at a point in the field is defined as the force per unit charge on a test charge placed at that point |
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Term
UNIT OF ELECTRIC FIELD STRENGTH |
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Definition
Newton per coulomb so NC-1 |
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Term
POSITIVE TEST CHARGES AT A CERTAIN POIN IN THE ELECTRIC FIELD |
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Definition
It will be acted by a force - F - due to the electric field. The electric field strength is then given the equation
electric field strength = force / charge
E = F / Q |
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Term
ELECTRIC FIELD STRENGTH NOTES |
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Definition
Electric field strength is a vector, it is in the direction of the force on a positive test charge. So the direction of field lines at any point is the same as the direction of the electrical field strength at that point.
Force = Same direction as electric field if positive charge
Opposite direction to field if negative charge
The test charge must be less than 1 coulomb so it doesn't alter the electric field strength |
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Term
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Definition
Metal rod at the top of a tall building. It's connected to the ground by a metal conductor which is very thick. When a charged cloud is overheated, a strong electric field is created near the conductor which ionises the air molecules. These ionised air molecules discharge the cloud which reduces the risk of lightning.
*Air is an insulator and is ionised by strong electric fields which pull elctrons out othe air molecules. |
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Term
ELECTRIC FIELD BETWEEN TWO PARALLEL PLATES* |
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Definition
Field lines between two oppositley charged flat plates are parallel to each other and at right angles to the plates. The lines go from the positive plate to the negative plate. This means the field is uniform not radial because the electric field strenght has the same magnitude and direction at all points |
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Term
ELECTRIC FIELD STRENGTH USING VOLTAGE |
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Definition
Electric field strength can be calculated using potential difference;
electric field strength = voltage / distance(seperation) between the two plates
E = V / d
This unit is Vm-1 |
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Term
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Definition
The force - F - on a test charge - Q -
Force = Charge x Electric field strength
F = QE
If charge - Q - is moved from positive plate to negative; work is done to move it. The field does this work on Q.
Work done = force x distance moved
W = Fd |
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Term
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Definition
The definition of potential difference - V - is the work done per unit charge when a small charge is moved through it.
Voltage = Work done / Charge
V = W / Q
Work done = Charge x Electric field strength x distance
W = QEd |
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Term
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Definition
This means that:
Voltage = (Charge x Electric field strength x distance) / Charge
V = QEd / Q
The charges appear on both sides of the divide sign so they cancel out
V = Ed so E = V / d |
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Term
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Definition
Electric fields are near any charged object or body. The greater the charge, the stronger the electric field.
- Charged metal conductors have thier charge spread across the surface, the more conecntrated the charge is, the greater the strength of the electric field |
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Term
ELECTRIC FIELD PATTERN BETWEEN A V-SHAPED CONDUCTOR AND FLAT PLATE: * |
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Definition
When a constant pd is applied, The field lines are more contcentrated (closer together) at the tip of the V plate, becasue this is where most of the charge is |
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Term
ELECTRIC FIELD BETWEEN TWO OPPOSITELY CHARGED PARALLEL PLATES |
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Definition
This depends on the concentration of charge on the surface of the plates. The charge on each plate is spread evenly across the surface of the plate facing the other plate
The elctrical field strength is proportional to the charge per unit area
E ≈ Q / A |
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Term
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Definition
Like charges repel and unlike charges attract |
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Term
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Definition
Electrons charge in most situations. Uncharged atoms contain equal numbers of protons and electrons. ADDING electrons, negatively charges the atom, REMOVING electrons positively charges the atom.
e.g when a perspex rod is rubbed with a dry cloth, the electrons from the rod transfer to the cloth. This removes electrons from the rod making it positive and adds electrons to the cloth making it negative |
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Term
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Definition
Metals contain lots of free electrons. These move about inside a metal and are not attatched to any one atom. They are the charge carriers. To charge a metal is must be isolated from the earth otherwise the charge will be neutralised by electrons transferring between the earth and metal. |
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Term
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Definition
If the conductor is charged postively, electrons from the earth transfer to the conductor to neutralise the charge. If negatively, the electrons from the conductor will transfer to the earth, discharging the conductor. |
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Term
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Definition
Don't contain free electrons, so all the electrons are attatched to individual atoms. Some insulators are easy to charge because thier surface atoms lose or gain electrons easily |
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Term
THE SHUTTLING BALL EXPERIMENT |
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Definition
Shows elecric current is a flow of charge
Conducting ball is hung by insulating thread between two vertical plates of opposite charge
When high voltage is applied, the ball bounces back and forth between the two plates
Everytime it touches the negative plates, electrons are transferred to the ball (so it's negatively charged) and repelled by the negative plate yet attracted by the positive plate. Here electrons transfer to the positive plate and the ball becomes positive and repelled again |
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Term
CURRENT CHARGE AND FREQUENCY |
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Definition
Current = Charge x Frequency
I = Qf
Frequency = 1 / time
Therefore current = charge / time for one cycle
I = Q/Time for one cycle
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Term
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Definition
Used to detect charge
If charged obejct is in contact with metal cap of electroscope, some charge transfers to electroscope which then flows to the gold leaf and metal stem causing them both to have the same charge so they repel each other. The leaf is light so as being repelled by the metal stem, it rises. If another object with the same charge is bought close too, this will cause the leaf to rise further as more charge is forced to transfer to the leaf and stem |
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Term
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Definition
The small amount of charge on pins of a microchip is enough to destroy the circuits inside a chip.
If the pins are touched by a charged near a charged object, they will be earthed. This means the electrons will transfer from the pins to the earth.
Microchips are stored in antistatic packets which allow charges to flow across the surface |
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Term
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Definition
Any two objects exert equal and opposite forces;
Electric fields surround each charge
If a small positive test charge is placed near an object with a much bigger charge that is also positive, the test charge will follow a path AWAY from the big charge. The path is called field lines |
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Term
FIELD LINES OF 2 OPPOSITELY CHARGED POINTS* |
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Definition
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Term
FIELD LINES OF A POINT NEAR A PLATE* |
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Definition
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Term
FIELD LINES OF TWO OPPOSITELY CHARGED PLATES* |
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Definition
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Term
OPPOSTIELY CHARGED POINTS |
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Definition
Create field lines which are concentrated at each point. Positive test charges would follow a curved path to the negative point charge |
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Term
POINT OBJECT NEAR AN OPPOSITELY CHARGED FLAT PLATE |
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Definition
Field lines concentrated at point object but at right angles to the plate; field is strongest where the field lines are most concentrated |
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Term
TWO OPPOSITELY CHARGED PLATES |
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Definition
Field lines run parallel from one plate to the other at right angles to the plates. This is a uniform field because the field lines are parallel |
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Term
THE VAN DE GRAAF GENERATOR |
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Definition
Produces sparks in the air
Charge created when a rubber belt rubs against a metal pad and is carried up the belt to the metal dome. As charge increases on the ome, the pd between the dome and earth increases until sparking occurs.
Sparks transfer energy from the dome. Work is done to charge the dome because a force is needed to move the charge on the belt up to the dome. Electric potential energy of the dome increases as it charges up. Some of this energy is transferred from the dome when a spark is created |
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Term
TWO OBJECTS OF THE SAME CHARGE |
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Definition
Work must be done to move a charged object towards another charged object of the same charge. Thier electric potential energies increases as they move toward each other |
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Term
CONSIDERING TWO CHARGED OBJECTS OF THE SAME CHARGE |
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Definition
The electrical potential of object 1 increases from zero at infinity, as it moves towards object 2. The electrical field of object 2 causes a repulsive force which acts on object 1 . Object 1 must overcome this force to move closer to object 2 |
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Term
ELECTRIC POTENTIAL AT A CERTAIN POSITION IN ANY ELECTRIC FIELD |
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Definition
The work done per unit positive charge on a positive test charge when it is moved from infinity to that position. |
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Term
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Definition
By definition, the position of zero potential energy is infinity |
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Term
UNIT OF ELECTRICAL POTENTIAL |
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Definition
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Term
THE RELATIONSHIP BETWEEN ELECTRIC POTENTIAL ENERGY (Ep) AND ELECTRIC POTENTIAL (V) |
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Definition
Electric potential = electric potential energy / charge
V = EP/Q
So
EP = QV |
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Term
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Definition
Lines of constant potential
Test charges moving along an equipotential has constant potential energy.
No work is done by the electric field because the force due to the field is at right angles to the equipotential -- lines of force of the electric field cross the equipotential lines at right angles |
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Term
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Definition
The potential gradient at any position in an electric field is the change of potential per unit charge of distance in a given direction |
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Term
POTENTIAL GRADIENT OF A NON - UNIFORM FIELD |
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Definition
Potential gradients vary with position and direction. The closer the equipotentials are, the greater the potential gradient is at right angles to the equipotentials |
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Term
POTENTIAL GRADIENTS IN A UNIFORM FIELD |
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Definition
If the field is uniform e.g two parallel plates that are oppositely charged, the equipotentials between the plates are equally spaced lines parallel to the plates. |
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Term
ELECTRIC POTENTIAL GRADIENT FACTS |
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Definition
The potential(negative) is proportional to the distance
The potential gradient is constant
The potential gradient increase in the opposite direction to the electric field
The potential gradient = electric potential / distance
= V / d |
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Term
ELECTRIC FIELD STRENGTH AND POTENTIAL GRADIENT |
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Definition
The electric field strength is equal to the negative of the potential gradient |
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Term
COULOMB'S LAW - LINK OF F AND r |
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Definition
The force is proportional to 1 / radius squared
From here Coulomb law states that:
Force = Constant of proportionality x Charge of one object x charge of second object / distance between them squared
Constant of proportionality = 1 / 4πεο
F = Q1Q2 / r2
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Term
SALT CRYSTALS DISSOLVING IN WATER |
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Definition
Salt crystals are ionic
Sodium ions and chlorine ions are oppositely charged
Electrostatic forces between them hold them together
Water weakens the electrostatic forces between the ions at the surface so they break free from the surface of the crystals, so they dissolve
The force in water is 80 x weaker than if the crystals were in air
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Term
COULOMBS LAW APPLIED TO THE FORCE ON A TEST CHARGE (q) |
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Definition
Force = Constant of proportionality x point charge x test charge / distance sqaured
F = kQq / r2
Electric field strength at distance (r) = Force / test charge = constant of proportionality x point charge / distance squared
E = F / Q = kQ / r2 |
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Term
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Definition
A charged obejct which effects distances much greater than it's own diameter |
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Term
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Definition
A test charge in an electric field is a point charge that doesn't alter the electric field in which it is placed - if the object has a charge that is greater than one coulomb, it would change the distribution of charge which creates the field |
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Term
POSITIVE POINT CHARGE AND POSITIVE TEST CHARGE |
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Definition
Field lines radiate away from point charge because the test charge in the field experiences a force directly away from the point charge wherever it's placed.
Coulombs law states that force = (one / four x pi x epsilon) x (point charge x test charge / distance squared)
F = (1/4πεο) Qq/r2
Electric field strength = force / test charge
so electric field strength = point charge / 4,pi,epsilon x distance2
E = Q / 4πεο x r2
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Term
WHAT IF THE POINT CHARGE IS NEGATIVE |
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Definition
If the point charge is negative using the formula; E = 4πεο x r2, the value of E will be negative so the field lines will
point towards the point charge |
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Term
ELECTRIC FIELD STRENGTH AS A VECTOR |
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Definition
If a test charge is in an electric field with 2 or more point charges, each charge exerts a force on the test charge.
The resultant force on the test charge gives the resultant electric field strength at the test charge |
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Term
FORCES IN THE SAME DIRECTION |
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Definition
For example a positive test charge between a negative point charge and positive point charge have forces in the same direction because the positive point charge repels the test charge and the negative point charge attracts the point charge
This means the resultant force is equal to the sum of both forces
F = F1 + F2 |
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Term
RESULTANT ELECTRIC FIELD STRENGTH FOR FORCES IN THE SAME DIRECTION |
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Definition
Force = electric field strength x charge
F = qE
Rearranging this gives electric field strength = force / charge
E= F/q
Resultant force = force from negative + force from positive
F = F1 + F2
So resultant electrical field strength is equal to (charge x electric field strength1 + charge x electric field strength 2) / charge
E = (qE1 + qE2) / q
Charge,q, cancels out to leave E = E1 + E2
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Term
FORCES IN OPPOSITE DIRECTIONS |
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Definition
A test charge between two positive point charges. The forces will be in opposite direction because the forces repel each other so the resultant force =
F = F1 - F2
Electrical field strength
E = E1 - E2 |
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Term
FORCES AT RIGHT ANGLES TO EACH OTHER |
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Definition
Pythagoras theorum
F2 = F12 + F22
Electric field strength
E2 = E12 + E22 |
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Term
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Definition
Electric field lines of force surrounding a point charge are radial - the equipotentials are circles around the point charge
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Term
THE ELECTRIC FIELD STRENGTH EQUATION |
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Definition
E = Q/4πεο r2
Shows that the electric field strength is inversely proportional
to the square of the distance. This is an inverse square law,
so shows a curve on a graph because
Electric field strength is proportional to1/r2 |
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Term
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Definition
Negative electric field strength means that the field is acting towards a negative charge
Negative electric potential means a value below zero
*E varies more sharply with distance than V |
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Term
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Definition
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Term
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Definition
CHARGE (Usually for point charges) |
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Term
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Definition
CHARGE OF ELECTRON
1.6 X 10-19 |
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Term
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Definition
FREQUENCY (1/time taken) therefore
1/f = time taken |
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Term
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Definition
ELECTRIC FIELD STRENGTH
E = F / Q (With test charges)
E = V / d (For two parallel plates) |
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Term
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Definition
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Term
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Definition
Force due to electric field strength
F = QE
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Term
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Definition
Work done
W = QEd
W = QV(Volts) |
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Term
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Definition
Epsilon nought
8.85 x 10-12 Fm-1 (Farads per metre) |
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Term
CONSTANT OF PROPORTIONALITY
COULOMB'S LAW |
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Definition
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Term
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Definition
F = K x Q1Q2 / r2
Force = constant x charge 1 x charge 2 / distance sqaured |
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Term
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Definition
Inversely proportional to the square of distance r
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Term
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Definition
Inversely proportional to distance r it's not an inverse square alw becasue v is proportional to 1/r.
V curve is always LESS steep than E curve |
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Term
NEGATIVE E AND NEGATIVE V |
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Definition
Negative E = field acts towards negative charge
Negative V = value less than 0
E varies with distance more sharply than V |
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