# Primary Science

## Primary/ PSLE Science: What affects the brightness of a bulb?

Have you ever wondered what makes a light bulb shine brightly and what affects its brightness? Recently, a curious Primary 5 student approached our teacher at Bluetree Education with this intriguing question.

In this article, we aim to shed light on this fascinating topic for Upper primary/PSLE students. Understanding the factors that influence bulb brightness not only satisfies our curiosity but also opens up a world of scientific exploration and discovery

Together, let’s uncover the magic behind bulb brightness and ignite a spark of wonder in your child’s mind. Get ready to explore the captivating science behind every glow and discover the fascinating world of light bulbs. Let’s shine a light on the captivating science behind bulb brightness

## This is the question on Bulb Brightness:

Jess has an electric circuit with two batteries and one bulb, bulb X. She decided to add in another bulb, bulb Y (shown in Figure 1) and her mother gave her another bulb, bulb Z, to form the electric circuit in Figure 2.

a) What happens to the brightness of bulb X after adding bulb Y? Explain why?

b) What happens to the brightness of bulbs X and Y after adding bulb Z? Explain your answer.

## Must-Know Electricity Concept for Upper Primary/PSLE students: Factors affecting Bulb Brightness

Understand that a light bulb is a circuit component that produces light using electricity. It is represented in a circuit diagram with this symbol:

### Factor #1: Number of batteries/ power source

An electrical system needs a power source to work. In this simple electrical system or circuit, it has wires which connect a bulb to a power source (e.g. battery). The bulb lights up when the electric current flows through the wire and the bulb and back to the power source.

Without a power source, there would not be (electrical) energy for the system to do work (i.e. to light up the bulb in the above electrical circuit). On the other hand, the more batteries an electrical system has, the brighter the bulb becomes because more batteries provide more electrical power to the circuit and the bulbs.

Note that too many batteries will overheat and make the bulb fuse instead.

Other than the presence of a power source or the number of batteries, let’s look at what are the other factors affecting the brightness of a light bulb.

### Factor #2: The arrangement of bulbs in an electric circuit

There are two arrangements in which bulbs can be arranged in, either in series or in parallel.

• When two or more bulbs are arranged in series, the electric current from the power source can flow through the bulbs in a single pathway (see the yellow highlight in SERIES).
• Whereas, when two or more bulbs are arranged in parallel, the electric current from the power source can flow through the bulbs in multiple (two or more) pathways (see the blue and red highlight in PARALLEL).

Considering two electrical systems with the same number of batteries. The bulbs arranged in parallel arrangement will be brighter than bulbs in series arrangement.

### Factor #3: The number of bulbs in an electric circuit

The number of bulbs added to an electric circuit will determine how bright the bulbs will light up. For bulbs that are added in series, the additional bulb(s) will share the electric current flowing through the circuit hence the bulbs will become dimmer.

For bulbs that are added in parallel, the additional bulb(s) will have the same amount of electric current flowing through and each bulb does not share the electric current. Hence, the brightness of bulb remains the same.

## Let’s go back to the questions:

Jess has an electric circuit with two batteries and one bulb, bulb X. She decided to add in another bulb, bulb Y (shown in Figure 1) and her mother gave her another bulb, bulb Z, to form the electric circuit in Figure 2.

### a) What happens to the brightness of bulb X after adding bulb Y? Explain why?

Bulb X will become dimmer. As bulbs X and Y are arranged in series hence them electric current is shared among the two bulbs and less electric current will flow through bulb X.

Explanation questions can be answered using the A.B.C. answering technique. First, “Answer with a choice” on whether bulb X will be brighter, dimmer or remain the same after adding bulb Y in series. Even though the options are not stated, students should know the possible changes in the brightness of a bulb.

Second, “Back with evidence”, which is writing the relevant information taken from the diagram. It is observed that bulb Y is added in series to bulb X.

Third, Confirm with concept”, to reason why bulb X is dimmer, as there is less electric current flowing through bulb X. Comparison words such as “dimmer” and “less” are important to show the difference between the two electrical circuits, with and without bulb Y.

### b) What happens to the brightness of bulbs X and Y after adding bulb Z? Explain your answer?

The brightness of bulbs X and Y will remain the same. Since bulb Z is added parallel to bulbs X and Y, the amount of electric current flowing through bulbs X and Y remains the same.

Similar to part (a), this explanation question can be answered using the A.B.C. answering technique. First, Answer with a choice” on whether bulbs X and Y will be brighter, dimmer or remain the same after adding bulb Z in parallel.

Second, Back with evidence”, to state the observed information from the diagram that bulb Z is added in parallel to bulbs X and Y.

Third, Confirm with concept”, to reason why the brightness of bulbs X and Y remain the same, as the amount of electric current flowing through bulbs X and Y is still the same.

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