Circuits – Bulbs Arranged in Series

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Observe the effect of arranging bulbs in series on the brightness of the bulbs in a simple electric circuit. Head to ngscience.com for a range of related resources.

Series Circuits
There are two main types of electric circuits – series circuits and parallel circuits. The circuits are different in the arrangement of the circuit components.

In a series circuit, the components are assembled in a way that there is only a single path along which electric current can flow.

In the series circuit below, the bulbs have been arranged in series. When output devices are arranged in series, the electric current is equally distributed among the output devices. When two bulbs are arranged in series, the bulbs will be less bright than if there was only one bulb.

In the series circuit below, two batteries are arranged in series. When batteries are arranged in series, more electric current flows through the circuit and the output devices. In the case of a bulb, arranging two batteries in series will result in the bulb glowing brighter compared to a bulb in a circuit with a single battery.

A bulb produces light and heat when electric current flows through a coiled wire inside the bulb called the filament. If too much current flows through the filament, it can overheat and break. If one of the output devices arranged in series breaks, the circuit is open and none of the output devices will function.

Simple Circuits
Use insulated copper wires to connect a light bulb, battery and switch in a closed loop. Close the switch and the light bulb lights up. Open the switch and the light bulb turns off. What causes these changes to occur?

Assembling the circuit components in a closed loop creates an electric circuit. An electric circuit is a path around which electricity flows. In an electric circuit, electrical energy flows from an energy source, through conducting wires, to an output device that changes the electrical energy into other forms of energy. A light bulb, for example, changes electrical energy into light energy and heat energy. A fan can change the electrical energy into kinetic energy, sound energy and heat energy.

For electric current to flow through a circuit, there must be a complete path along which the electrical energy can flow. A switch is often used to control the flow of electrical energy by opening and closing the path.

When a switch is in the ‘on’ position, there is a complete path for electrical energy to flow. The circuit is closed. When the switch is in the ‘off’ position, the circuit is open and electric current cannot flow. An electric circuit may also be open if the circuit components are not connected properly or are broken in some way.

Parallel Circuits
In a parallel circuit, the components are assembled in a way that there is more than one path along which electric current can flow.

In the parallel circuit below, the bulbs are arranged in parallel. Use your finger to trace along the wires and you will see that there are two paths along which the electric current can flow. Two bulbs arranged in parallel will glow brighter than if they were arranged in series.

An advantage of arranging output devices in parallel is that if one device was to break, there still remains a complete path for electric current to flow. As such, the output devices along the complete path will continue to function. In the parallel circuit above, if one bulb was to break, the other bulb will continue to light up.

Multiple batteries can also be connected in parallel. When batteries are arranged in parallel, such as those in the circuit below, the current flowing through the circuit and output devices is the same as if there was just a singe battery. Therefore, a bulb in a circuit with two batteries arranged in parallel is equally as bright as when connected to one battery.

An advantage of arranging batteries in parallel is that they will last proportionally longer. This means two batteries in parallel will last twice as long as a single battery.