physics topic 4 - starec.enschool.org
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Physics Topic 4
Electricity and Magnetism
Electrostatics
Charged Objects
• Charges come about from electrons moving
Conservation of Charge
• Total charge of a system remains constant
Coulomb’s Law
• Unit for charge = Coulomb (C) = 6.25 x 1018
• Charge of an electron = -1.6 x 10-19 C• Charge must be a whole number multiple of
the charge of an electron!!!
Electric Fields
• Electric field line – imaginary line along whicha positive test charge would move in anelectric field.
Potential Difference• If a charged particle’s motion opposes the
direction of an electric field, work must bedone to move it.
• Amount of work to move an elementarycharge against an electric field with a potentialdifference of 1V
= 1 electronvolt (eV) = 1.60 x 10-19 J
Electric Current• Current – the rate at which charges pass a
given point in a circuit• Circuit – closed path along which charges
move• Switch – device tomake, break, orchange connectionsin a circuit
Current (I)
• Measured by ammeter• Units are Amperes, A
Conductivity• Conductors – material in which electrons
move readily• Insulator – material in which electrons do not
move readily
Ohm’s Law
• Resistance (R) – opposition that a device offersto the flow of electrons.
• Measured in ohms (Ω)
Resistance• Resistivity, ρ, depends on electronic structure
and temperature.• Resistance is directly proportional to resistivity
and length of wire• Resistance is inversely proportional to the
cross-sectional area
Resistors
• Resistor – device with a definite amount ofresistance. Used to limit current.
• Variable Resistor – amount of resistance canbe changed
Electric Circuits
Series Circuits
• All parts are connected end to end to providea single path for the current
Parallel Circuits
• Elements are connected between two points,with one of the two ends of each componentconnected to each point
More Equations
Magnetism• Magnets have 2 Poles (North and South)• Magnetism – force of attraction between
magnetic poles• FUN FACT – Earth’s South Magnetic Pole is the
Geographic North Pole and vice-versa
• Strength of field = density of field lines
Electromagnetic Induction
• Induced Potential Difference – a voltagecreated in a conductor due to its motion in amagnetic field.
• An electromagnetic wave is formed when oscillating oraccelerating electric charges produce changing electricand magnetic field