# Physics Topic 4 TAKE TWO

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• FIIELDS
• Electric fields
• A region of space which causes charged particles to experience a force
• Uniiform elecric field
• Strength = how rapidly the potential changes
• Equipotentials = connections between places of equal potential
• Coulomb'sLaw
• An attraction between a proton and electron can be imagined as proton creating an electric field and the  eltron experiancing this force
• Eo = permativity of free space
• Capacitors
• Charging capacitor- when power supply is connected the electric field created in conducting wires causes electrons to move towards positive terminus and since they cannot follow across the gap they build up in positive terminus thus making it negatively charged
• the attraction between opposte charges on the two plates causes an electric field between plates which eventually = the pd of power supply
• Store of charge - amount of charge stored is its capacitance
• stores electrical potenialenergy
• Discharging- at first the  flow of electrons high  (attraction repulsion is high) pd between gap reduces
• Generating Electricity
• Electromagnetic induction- if we move a magnetic near a wire  the electrons will feel a force making them move through the wire - creating a emf
• by coiling up a wire the magnetic field will have more effect - magnetic flux linkage
• Faradays law - emf is proportional to the rate  of change of flux linkage
• Lenz Law - the direction of inducedemf is such to oppose the charge creating it
• thumb - motion first finger field second finger included emf (RIGHT HAND)
• Magnetic Fields
• Force on wire = strength of magnetic field x current x length i=of wire x sin angle between current and magnetic field
• F = BIL
• motor more powerful if I increases, length of wire increases or magnetic field increases
• Flemmings left hand rule thumb: direction of motor effect first finger field and second finger current
• The quantity of flux (weber) through any given area indicates the strength of the effect of the field there
• Magnetic field strength - number of lines - magnetic flux density
• A region of space which causes a magnetic pole to experience a force
• Motor effect happens because charged particles move at right angles to force, magnetic field and if the electron is constrained in a wire then force is transferred to wire
• Force on a charged particle moving across magnetic field = charge of particles velocity of particle x sin angle between velocity and magnetic field
• F = BEV
• Generating Electricity
• Electromagnetic induction- if we move a magnetic near a wire  the electrons will feel a force making them move through the wire - creating a emf
• by coiling up a wire the magnetic field will have more effect - magnetic flux linkage
• Faradays law - emf is proportional to the rate  of change of flux linkage
• Lenz Law - the direction of inducedemf is such to oppose the charge creating it
• thumb - motion first finger field second finger included emf (RIGHT HAND)
• Magnetic Fields
• Force on wire = strength of magnetic field x current x length i=of wire x sin angle between current and magnetic field
• F = BIL
• motor more powerful if I increases, length of wire increases or magnetic field increases
• Flemmings left hand rule thumb: direction of motor effect first finger field and second finger current
• The quantity of flux (weber) through any given area indicates the strength of the effect of the field there
• Magnetic field strength - number of lines - magnetic flux density
• A region of space which causes a magnetic pole to experience a force
• Motor effect happens because charged particles move at right angles to force, magnetic field and if the electron is constrained in a wire then force is transferred to wire
• Force on a charged particle moving across magnetic field = charge of particles velocity of particle x sin angle between velocity and magnetic field
• F = BEV