Electricity 2: Resistance and Electric Circuits

Resistance and Electric Circuits

By Akram Varqid

Revision

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: The river stones

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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Multiple Choice

If voltage is 5 V, and current is 2 A, what is the resistance?

• 10 Ω

• 2.5 Ω

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

Ohmic or non Ohmic?

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Ohmic vs non ohmic graph

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Multiple Choice

This graph is for

• Ohmic wire

• Tungsten lamp

Each component is on different line

Have junction​

Parallel Circuits

Component connected one by one on a single line

No junction​

Series Circuits

Type of electric circuits

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Diagram of series and parallel

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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

Series Circuit

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Multiple Choice

(5min) 24V will go through 1Ω, 2Ω and 3Ω. As the voltage is different through each resistance, more resistance more voltage. Using ratio, 24 V going through 6Ω, 4V for each Ω. How much V going to 2Ω resistor?

• 4V

• 8V

• 12V

Multiple Choice

Which is series circuit?

• C

• D

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

Parallel Circuit

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Multiple Choice

(5min) Calculate the total resistance

• 32/3 Ω​

• 3/32 Ω​

• 48Ω​

Multiple Choice

Given total resistance is 10.7Ω​. Using V=IR, What is the total current?

• 128.4 A

• 1.12 A

• 0.891 A

Multiple Choice

Given total current 1.12 A, going through resistance R1 and R2. As this is parallel, current different through each line. R2 is double from R1. We can ratio as 3. If 1.12A divide by 3 get 0.37A, what is current flowing to R2?

• 0.37 A

• 0.74 A

Multiple Choice

Given total current 1.12 A, if current flowing R2 is 0.74A, what is current flowing to R1?

• 0.37 A

• 0.74 A

Resistance of a wire

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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Multiple Choice

From formula R = (ρ​ x l ) / A

What happen to resistance if the crossection area is doubled?

• Doubled

• Halved

Multiple Choice

From formula R = (ρ​ x l ) / A

What happen to resistance if the resistivity is doubled?

• Doubled

• Halved

Multiple Choice

From formula R = (ρ​ x l ) / A

What happen to resistance if the length is halved?

• Doubled

• Halved

Open Ended

Give your ID Number (AB123456)