Download 5.1 Electric potential difference, current and resistance

Electric Currents
Topic 5.1 Electric potential difference,
current and resistance
Simple Circuit
• What does a simple circuit
include?
• Circuit implies a flow. What is
flowing?
• How do you know there’s a
transfer of energy?
• Can we see any of this?
Analogy
Advanced Analogy
Energy
Added to
the
System
Energy
Removed
from the
System
Definitions
• What are charges?
• How do we use charges to
produce potential
movement?
• What happens when there
is a charge in the middle?
Energy between metal plates
• What needs to be done to move a
negative charge from the red to
blue plate?
• What happens to the charge when
it’s at the blue plate?
• What happens when it’s released?
Potential Difference
• Energy needed to move a charge from A to B
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cell
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energy
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electron
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lamp
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Current
• What is current?
• How would we measure current?
Conventional
Current
Electron Flow
Resistance
• What is electrical resistance?
Ohm’s Law
Ohmic vs Non-Ohmic Resistors
Back to the Electric Circuit
• Where does the energy come
from in an electric circuit?
• Where does the energy go?
• What determines the amount
of energy that is ‘taken’?
• What is carrying the energy?
Definitions
• Charge, Q
• Current, I
• Potential Difference, V (Voltage)
• Resistance, R
• If units of charge are
coulombs [C], derive
the units for I, V, and R
Definitions
• 1 coulomb = 6 x 1018 electrons of charge
• Current, I
• Potential Difference, V (Voltage)
• Resistance, R
• If units of charge are
coulombs [C], derive
the units for I, V, and R
Definitions
• 1 coulomb = 6 x 1018 electrons of charge
• Current = Charge / Time
• Potential Difference, V (Voltage)
• Resistance, R
• If units of charge are
coulombs [C], derive
the units for I, V, and R
Definitions
• 1 coulomb = 6 x 1018 electrons of charge
• Current = Charge / Time
• Potential Difference = Energy / Charge
• Resistance, R
• If units of charge are
coulombs [C], derive
the units for I, V, and R
Definitions
• 1 coulomb = 6 x 1018 electrons of charge
• Current = Charge / Time
• Potential Difference = Energy / Charge
• Resistance = Voltage / Current
or
Units
𝑄 [𝐶]
𝐼= =
= 𝑎𝑚𝑝𝑒𝑟𝑒 = 𝐴
𝑡
[𝑠]
𝐸 [𝐽]
𝑉= =
= 𝑣𝑜𝑙𝑡 = 𝑉
𝑄 [𝐶]
𝑉 [𝑉]
𝑅= =
= 𝑜ℎ𝑚 = [Ω]
𝐼 [𝐴]
The electron volt (eV)
• One electron volt (1 eV) is defined as the
energy acquired by an electron as a result
of moving through a potential difference
of one volt
• 1 eV = ? J
The electron volt (eV)
• One electron volt (1 eV) is defined as the
energy acquired by an electron as a result
of moving through a potential difference
of one volt
• 1 eV = 1.6 x 10-19 J
Inside the wire
Wire = Resistor
• What happens when the electrons collide
with the atoms?
• What happens to the atoms when the wire
is at a higher temperature?
• How does this affect the resistance of the
wire?
Power Dissipation
•𝑃 =
•𝑃 =
•𝑉 =
•𝐼 =
𝑊
𝑡
𝐸
;
𝑄
𝑄
;
𝑡
=
𝐸
𝑡
𝐸 = 𝑉𝑄
𝑡=
𝑄
𝐼
𝑉𝑄
𝑄 𝐼
= 𝐼𝑉
• 𝑉 = 𝐼𝑅;
𝑃 = 𝐼 𝐼𝑅 = 𝐼2 𝑅
•𝐼 =
𝑉
;
𝑅
𝑃=
𝑉
𝑅
𝑉=
𝑉2
𝑅
In summary