PHYS - Series vs. Parallel Electric Circuits

For IGCSE Physics, you should be able to compare series and parallel electrical circuits 😁

Series Circuit

When a circuit is connected in series, electrical components are connected next to each other in a single loop.

Two lamps connected in series looks like this 👇

• In a series connection, the same amount of current flows through the electric components. 
• The potential difference supplied by the cell is equal to the sum of the potential difference across different components.
• The total resistance of the circuit is the sum of the resistance of each component.

• _Itotal = I₁ = I₂ 
• _Vtotal = V₁ + V₂ 
• _Rtotal = R₁ + R₂ 

Parallel Circuit

When a circuit is connected in parallel, electrical components are connected to each other, forming another loop.

Two lamps connected in parallel looks like this 👇

• When a flowing current meets the branched loop, the current will split into the two branches. Therefore, the sum of the current in each component is equal to the total current following in the circuit.
• The potential difference supplied by the cell is equal to the potential difference of each component.
• The total resistance of the circuit is less than the resistance of each component.

Example I

20 lamps are connected in series with a 9 V supply. 

(a) What is the voltage across each lamp in the series circuit?

Since 9 V is shared across the 20 lamps, voltage across each lamp is equal to 9 / 20 = 0.45 V.

(b) Each lamp has a power of 1.5 W. Show that the current in the circuit is about 3 A.

P = VI

The current through each lamp is: 

I = P / V

= 1.5 / 0.45

= 3.3 A

Since the same current flows through each lamp in a series circuit, the current in the circuit is about 3 A.

Frequently asked in IGCSE Physics 👉

Example II

What are some advantages and disadvantages of connecting lamps in parallel rather than in series?

Advantage of parallel circuit: 

• By connecting a switch next to each lamp on each branch, the lamps can be turned on and off separately. If the lamps were connected in series, you would have to turn on and off all of the lamps together.
• Even when there is a fault in one of the lamps, all the other lamps can function normally. In a series connection, a fault in one of the lamps will break the circuit affect all other lamps in the circuit as well.

Disadvantage of parallel circuit:

• Parallel circuits use more wiring than series circuits.

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