Volt (The amount of push) and the nature of pathway (conductivity) determine the amount of current flow.
Opposition of flow – Resistance means the pathways of the circuit are more difficult to flow.
Equation: R(Ω) = V(V)/I(A)
R: Resistance, measured in ohm (Ω)
V: Voltage, measured in volt (V)
I: Current, measured in amperes (A)
The ratio of V/I is called Ohm’s law (George Simon Ohm), and it is constant.
Conductor’s Resistance depends on:
| Length | Longer: More resistance | R1/R2=L1/L2 |
| Cross-sectional area | Larger Cross sectional area: Less resistance | R1/R2=A2/A1 |
| Type of Material | Higher Ressistivity (Ω*m): More resistance | R1/R2=p1/p2 |
| Temperature | Higher Temperature: More resistance | Not for all substances |
Example of calculating resistance:
R1/R2=L1/L2
R2=R1(L2/L1)
R2=1.7 Ω(50m/200m)=0.42 Ω
Superconductivity: Ability of a conductor conducting electricity without heat loss due to resistance.
Highest temperature superconducting materials, HTS, can reach the temperature of 140K (-133°C)
Series and Parallel Circuit
Kirchhoff’s current law: The total amount o f current into a junction point of a circuit equals the toal current that flows out of that same junction
Kirchhoff’s voltage law: The total of all electrical potential decreases in any complete circuit loop is equal to any potential increases in that circuit loop.
Kirchhoff’s laws prove that in any circuit, there is no net gain or loss of energy.
(Because of conservation of electric charge and the conservation of energy)
Resistances in a Series Circuit
· A single path way
· Current through each resistor is the same
· Sum of all potential energy loss through each resistor is equal to the total voltage
From Kirchhoff’s law, We know that
From Ohm’s law R=V/I, We get
Resistances in a Parallel Circuit
· More than 1 pathway
· Voltage is the same through each resistor
· Sum of the currents flowing into a junction point is equal to the amount of currents flowing out of the same junction.
From Kirchhoff’s law, we know that
From Ohm’s law R=V/I, We get
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