Electric Current and Ohm’s Law
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Conductors
• Electric conductor is a material through which
charge flows easily.
• What types of things would be good
conductors?
• Ex. Copper and silver
Superconductor
= a material that has almost no resistance when
it is cooled to low temperatures
Uses: MRI, Maglev trains (levitate train above
magnetic rails)
http://www.superconductors.org/tc_graph.gif
Insulators
• Electrical insulators are materials through
which charge does not flow easily.
• What are types of materials that would be
good insulators?
• Ex. Wood, plastic, rubber, air
Resistance
• When electrons flow, they collide with ions
and other electrons, so lose some energy
• Less energy = less current
• Resistance - “R”= opposition to the flow of
electrons in a material
• Measured in Ohms - “Ω” = symbol
What affects resistance?
• Thickness – higher thickness = less resistance
lower thickness = more resistance
• Length – shorter wire = less resistance
longer wire = more resistance
• Temperature – as temperature increase,
resistance increases due to more collisions
Ohm’s Law
• 1826 – Georg Simon Ohm
• Discovered relationship between voltage,
current and resistance
• the amount of current is directly proportional
to the voltage and inversely proportional to
the resistance of a circuit.
V=IxR
where
V = voltage (volts)
I = current
(amps)
R = resistance (ohms)
So:
- if you double the voltage, then
you will double the current
- If you double the resistance, the
current will be half of what it
was
What is the voltage of a circuit that has a
current of 12 amps and a resistance of 10
ohms?
What is the current of a circuit that has a
voltage of 9 volts and a resistance of 5
ohms?
What is the resistance of a circuit that has a
voltage of 12 volts and a current of 3 amps?