What are series and parallel circuits

Let’s understand how electricity works.

At your Primary school level, you need to know batteries provide a source of electrical energy.

When a circuit is closed, electricity flows in the circuit.

 

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What is a closed circuit?

Two conditions MUST be fulfilled

  • Wires are connected properly in the circuit (that means wires are connected to the light bulb properly. There is no breakage in any parts of the wires).
  • The wire is connected from the positive end of the battery to the negative end of the battery.

 

When ALL the conditions are met, the circuit is closed and electricity flows.

An example of a closed circuit.

*wires are properly connected to the bulb.

* Wires are connected from positive end to negative end of the battery.

In a closed circuit, what happens to the circuit components?

 

Take note of the proper explanations:

When the circuit is closed, the electricity flows across the bulb, the bulb lights up.

When the circuit is closed, the electricity flows across the buzzer, the buzzer sounds.

When the circuit is closed, the electricity flows across the heating strip, the heating strip heats up.

 

The diagram showing a closed circuit.

* Finding hard to visualise how electricity flows in a closed circuit? Use a pencil to draw the flow of electricity in the circuit. You can follow me and draw using arrows.

 

Proper explanation

The circuit is closed, the electricity flows across the bulb, the bulb lights up.

Note:

A) In Primary school syllabus, we learnt electricity flows from positive to the negative end of the battery.

In lower secondary syllabus and beyond, the actual flow of electricity is from the negative end to the positive end of the battery.

B) If you want the electricity to flow from the negative end of the battery, you can do so. It will give you the same results of which bulb lights up or don’t light up.

 

You can choose either option A or option B. Once you decided on that, be consistent and stick to that particular option. Both options give the same results.

Let’s check your understanding

 

A student uses a pencil to draw the flow of electricity (represented as the arrows) in the circuit. Is the student’s drawing correct?

The answer is wrong.

 

Why?

Remember this condition:

  • Wires MUST BE connected from positive to the negative end of the battery

Since the switch is open, there is a break in the wire (as shown in the diagram below). Wires are not connected from the positive to the negative end of the battery.

When that happens, no electricity flows across the bulb.

*switch is open indicating a break in the connection.

How about this circuit? Which bulb(s) light up?

Study the electrical circuit shown below. You can see this is still a closed circuit.

Some parts of the circuit are closed. Why is that so?

Recall the two criteria for closed circuit

  • Wires are connected properly in the circuit.
  • The wire is connected from the positive end of the battery to the negative end of the battery.

Since the wires connected to bulb A fulfilled both criteria, only bulb A lights up.

* Hard to visualise how electricity flows in a complex circuit? Use a pencil to draw the flow of electricity in the circuit. You can follow me and draw using arrows.

 

Proper explanation

The circuit is closed, the electricity flows across bulb A. Bulb A lights up.

As the switch is open, no electricity flows across bulb B. Bulb B does not light up.

Let’s compare the series and parallel circuits

What happens when we add or remove electrical components?

 

This is where it gets interesting.

Like a detective spotting for clues, spot the situations and remember the effects on the brightness of the bulbs.

There’s the bulbs arranged in series or parallel.

There’s the batteries arranged in series or parallel.

Do remember the proper explanation of every situation

What happens when we rearrange the batteries and bulbs?

Bingo!

That is the hallmark of a curious science student.

Always give yourself examples to test the concepts.

Let’s see what happens.

 

  • Rearrange the bulbs from series to parallel. What happens to the brightness?

The bulbs shine brighter when the bulbs are rearranged to be parallel to each other.

Explanation:
In parallel arrangement, more electricity flows across each bulb than the bulbs in series arrangement. Hence, the bulb shines brighter.

 

  • Rearrange the batteries from series to parallel. What happens to the brightness of each bulb?

Each bulb shines dimmer.

Explanation:
In parallel arrangement, the batteries provide less electricity across the bulbs compared to the batteries arranged in series. Hence, the bulb shines dimmer.

Application of science concepts

 

Mary set up a bicycle as shown below. She connected wires to the lamps on her bicycle. This is represented by a circuit diagram drawing.

She noticed the lamps are dimly lit.

Without making any changes to the lamps or the wires, suggest a way for her to make the bulbs shine brighter?

 

Analysis:

We cannot change the lamp nor the wires. We can only change the batteries.

Which situation is that?

Situation 3(A)

Hence, you can either add more batteries or change to a brand new battery.

 

Let’s look at the wrong answer.

Wrong answer

Add more batteries

 

Huh?

What’s wrong with that answer?

 

Teachers’ comments:

The answers lack details. Are you adding batteries in series or parallel?

Failure to write “series” or “parallel” has serious consequences to the brightness fo the bulb.

Hence, you need to tell the teacher what is the correct arrangement.

 

Correct answer

Add more batteries in series.

What can we take away from this revision notes?

Remember all the situations. They are crucial to determining the brightness of the bulbs.

When you add or remove batteries / bulbs in the parallel arrangement, there is no change to the brightness of the bulbs.

Take note of the proper answering technique to explain why a bulb lights or does not light up.

Take note of adding bulbs or batteries. The series or parallel arrangement must be stated clearly.


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