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Class notes Applied Physics (PSYCS1)
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Applied Physics Magnetic Laws and Motion Notes.
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Chapter 34: Electric Current• Electric current is simply the flow of electric
charge.
• Electric current is measured in amperes.
• An ampere is the flow of 1 coulomb of charge per
second.
• Charges will flow from one end of a conductor to
the other when its ends are at different electric
potentials. In other words, a potential difference
exists. Note: The wire itself has no net charge.
• The flow will stop when the potential difference
is zero.
, Voltage Sources
• Voltage sources provide a potential difference. It is this
potential energy per unit charge (sometimes called an
electromotive force or emf) that provides the “electric
pressure” to create a steady flow of electrons.
• In electrochemical sources such as dry & wet cells,
energy is released in a chemical reaction and converted
to electric energy.
• In generators mechanical energy is converted to electric.
• In photoelectric devices such as solar cells, light is
converted to electric energy.
• Other sources include piezoelectric (pressure to electric)
and thermoelectric (heat to electric) devices.
, Electric Resistance
• Electrical resistance is the resistance that a
material has to the flow of electric current.
• Electrical resistance is measured in ohms
(named after Georg Simon Ohm).
• Conductivity is the property of a material that
determines how well it transports electricity.
• Thin wires have more resistance than thick
wires; longer wires have more resistance than
shorter wires; and increases in temperature
generally increases resistance.
, Ohm’s Law
• Ohm’s Law states that current is directly
proportional to voltage and inversely
proportional to resistance.
• I = V/R or V = IR
• Thus, 1 ampere = 1volt/ohm
• Resistors are devices used in circuits that
regulate the current.
• Examples: A lamp cord is much less than 1
ohm, a light bulb has a resistance of about 100
ohms, toasters about 20 ohms. The greater the
resistance the smaller the current flow.
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