Physics unti 5 - Electric and Magnetic fields.
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- Created by: Phil
- Created on: 12-04-13 16:17
Electric field strength at a point
is the force per unit positive charge at the point.
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What is an elecrtic field?
A region in which there are forces on charges.
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What is the equation for electric field strength and what is the unit it is measured in ?
E = F/Q unit is NC^-1
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In a uniform field,How is the electric field strength found, what is it measured in?
E = V/d, measured in Vm^-1
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In a radial field, how is the force between two point charges found and what is this equation known as?
F = Qq/ 4πϵ0r^2, this equation is known as Coulomb's Law.
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What does Coulomb's Law state?
Any two charged particles exert a force on each other that is proportional to each of their charges and inversely proportional to the square of the distance between them.
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In electric fields, what do the lines represent and where do they go to/from?
Electric field lines show the direction of the force and the strength (represented by how close together the arrows are, the closer they are, the stronger the force.) They go from positive to negative.
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How is the kinetic energy of a particle in an electric field found?
The EF does work on the particle which is equal to qV. As a result of the work done, the particle gains Ke, so we can write 1/2mv^2 = qV.
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In an electric radial field, how is the EFS found?
E = 1/4πϵ0 Q/r^2, where r is the distance the point charge Q is at.
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What are the two units for electric field strength?
VM^-1 or NC^-1
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Differences between gravitational fields and electric fields? (3)
Gravi always attractive, ef can be attractive or repulsive. gravi = relatively weak, ef=relatively large. In gravitational, mass induces a force, in ef it is the charge that induces.
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Similarities between gravitation fields and electric fields? (2)
Both are proportional to 1/r^2. Both are Vectors.
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Define magnetic field.
A region where a force is exerted on a current-carrying conductor or a moving charge
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Where do magnetic field lines go to and from?
From the north to south.
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What two types of magnets can induce a magnetic field?
Permanent magnets and electromagnets.
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What is a permanent magnet?
A magnet that had a north and a south pole and has magnetic fields around it that cannot be turned off.
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What is an electromagnet?
A Temporary magnet that produce magnetic field by the flow of current. If the current is stopped then the magnetic field is turned off.
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Describe the right hand grip rule.
Thumb points in the direction of the current. The fingers curl to dhow the direction of the field.
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What is a solenoid?
Many coils, close together. Each coil produces a field that combine together.
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What causes force on a current carrying conductor.
The interaction between the two magnetic fields.
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How is the direction of the force on a current-carrying conductor found?
Use of fleming's left hand rule, field first finger, current second and force thumb.
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Define magnetic flux density.
is the force acting per unit current in a wire of unit legnth, where force, current and flux density are mutually perpendicular.
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What is the unit of flux density, define this unit.
A Tesla.! Tesla exerts a force of 1 unit force on a conductor of unit legnth carry a unit current at right angles to the field.
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What happens when a current flows so as to cut across lines of magnetic flux, and how is the force exerted found?
A force is exerted on the current carrying wire. F = BILsin(pheta) Where pheta is the angle between the current carry conductor and the magnetic flux that it is cutting.
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How is the force on a moving charged particle found, how is this equation found?
F=BQv, The equation is found from F=BIL by the use of I=Q/t and V=L/t and subbing these equations in.
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How is total flux found, what is it measured in?
By multiplying the flux density by the area. (total flux) = BAcos(pheta) where pheta is the angle the coil makes with the direction. It is measured in Webers WB
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Define the Weber.
1 weber is the flux produced when a magnetic flux density of 1T passes at right angles through are 1m^2. 1wb = 1tm^2
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Define magnetic flux linkage.
The product of the total flux and the number of turns in the coil.
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How can we find the emf induced from the magnetic flux linkage, what law is this?
Dividing the magnetic flux linkage by time, gives the emf induced. This is Faraday's Law.
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State Faraday's Law.
The magnitude of induced emf = -rate of change of magnetic flux linkage.
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State Lenz's Law.
An induced emf will be established so as to oppose the change that is producing it.
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How do ac generators provide an alternating current?
It is created by a taut coil being rotated around a uniform magnetic field. When the coil is perpendic to the field max emf is produced to oppose the motion (Lenz), when parallel no emf is produced. When reversed perp max (reversed) emf is produced.
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Why are AC generators efficient to run?
Resistance can be reduced by transforming electricity.
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What two ways do transformers change the resistance of the a.c ?
Step up - number of turns on the secondary coil is greater than the primary. Increasing Voltage and decreasing current. Step down - number of coils on the primary > no. of coils on the secondary. Decreasing voltage and increasing current.
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How do transformers work?
The input a.c voltage produces a varying magnetic field in the core. This induces an emf on the secondary coil due to the flux linking the together. Transforming the electricity is done through changing the turns-ratio.
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What is the transformer equation?
Vp/Vs = Np/Ns = Is/Ip Where V is voltage, I is current, N is number of turns on the coil, p is primary and s is secondary.
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Other cards in this set
Card 2
Front
What is an elecrtic field?
Back
A region in which there are forces on charges.
Card 3
Front
What is the equation for electric field strength and what is the unit it is measured in ?
Back
Card 4
Front
In a uniform field,How is the electric field strength found, what is it measured in?
Back
Card 5
Front
In a radial field, how is the force between two point charges found and what is this equation known as?
Back
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