Electricity 2: Resistance and Electric Circuits

What you need to know already

Charge, Q = ne, where e = 1.6x10^-19

​Current, I = Q/t where t is time

Voltage, V = W/Q where W is work @ energy​

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Resistance slows current movement

Resistance is inversely proportional to current, directly to voltage

The higher R, the lower the I @ the higher the V

Resistance can be related to Voltage and Current

R = V / I and its unit is Ohm @ Ω​

​This is called Ohm's Law

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Graph will not be straight, meaning that gradient which represent R is different at different I and V

Example: Filamen bulb​

Non Ohmic Conduc..

Follows Ohm's law R=V/I

If V is y axis, I is x axis, R will be gradient, and R will be 1 value (straight line)​

Example: Ohmic resistor​

Ohmic Conductor

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Each component is on different line

Have junction​

Parallel Circuits

Component connected one by one on a single line

No junction​

Series Circuits

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Ammeter is connected like this

​Voltage is different across each component

V_T = V₁ + V₂ + V₃

Current is equal everywhere for one line.

I_T = I₁ = I₂ = I_3​

Resistance is added directly

R​_T = R₁ + R₂ + R₃

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Voltmeter is connected like this

​Voltage is same across each component

V_T = V₁ = V₂ = V₃

Current is equal everywhere for one line.

I_T = I₁ + I₂ + I_3​

Resistance is added inversely

1/R​_T = 1/R₁ + 1/R₂ + 1/R₃

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Wire properties will affect its resistance

Longer wire = Higher resistance (Directly proportional)

Thinner wire = Higher resistance (Inversely proportional)

Less conductive material = High resistance​ (Directly proportional)

R = (ρ​ x l ) / A

where ρ = resistivity, l = length, A = cross section area

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