# Basic Lighting Circuit

In this project, you will learn how to construct a basic circuit to light an LED with a battery.

## Basic Circuit Components

An electrical circuit consists of three components:

1. A power source such as a battery.

Batteries are just one example of a power source. In future activities you will learn about different sources of electrical power. For now, think of batteries as storage containers for electrical power. The photo above shows an example of a battery found in electric circuits.

What do you notice that is similar in all the batteries?

2. An electrical component powered by the source such as a light.
An electrical component is anything to is powered by electricity, like the device you will use to do this activity. Electrical components are the things that we are interested in using to accomplish some other task. For example, electric motors are found in electric cars, which we use to get around from place to place.
Can you think of other electrical components?

3. Wires that connect the power source to the load. Electrical wires conduct electricity (electrical current) from the battery to the electrical component. Think of wires as the roads in which electrons travel on. The above photo shows a common electrical wire made out of copper. Wires can be made out of anything that conducts electricity.

## Open and Closed Circuits

When the wires are all connected, the circuit is complete, and power is delivered to the electrical component. When one of the wires is disconnected, the circuit is incomplete, and the component does not receive any power.

An electric switch is a device that can stop or allow electricity to flow through an electrical circuit:

(1) open (incomplete circuit)

(2) closed (complete circuit)

When the switch is closed, it completes the circuit, allowing electrical current to flow. An alligator clip (wire) can be used to complete the circuit, serving as a rudimentary switch. Below is a diagram of a closed circuit used to light up an LED.

Figure 1. A circuit with LED, battery, and wires.

## Resistance, Current, and Voltage

The flow of electricity in a wire is like the flow of water in a hose. There are three major factors that affect the flow of water in a hose. Each of these elements has an electrical counterpart.

1. Water pressure is the amount of water in a bucket. The amount of water or water pressure affects the rate at which the water flows through the hose.

2. Resistance to the flow of water is increased or decreased by adjusting the valve in the water faucet. The rate at which the water flows through the hose is adjusted by opening the valve (decreasing resistance) or closing the valve (increasing resistance).

3. The amount of water that flows through the hose is increased by increasing the water pressure and decreased by increasing resistance.

The amount of water is adjusted to meet specific needs. The water valve can be opened completely in order to quickly fill a bucket. It can be partially opened to produce a more moderate flow to water plants.

Figure 2. Decreasing resistance by opening a valve increases water pressure

When the valve is closed, the water pressure on the right-hand side of the valve is zero. When the valve is opened, the water pressure on the right-hand side of the valve increases. As the valve is opened, (1) the resistance to the flow of water decreases, and (2) the flow of water current increases. (Note: The height of the water affects the water pressure.)

 Table 1. Water and Electrical Analogy Water Electricity Units Water Pressure Electrical Force Volts Resistance Electrical Resistance Ohms Amount Electrical Current Amps

The electrical counterparts of water pressure, resistance, and amount of water flowing through a hose are summarized in the table above. Electrical force, measured in volts, is the equivalent of water pressure. Electrical resistance, measured in ohms, is the electrical counterpart of resistance to the flow of water in a hose. Electrical current, measured in amps, is the electrical counterpart to the amount of water flowing through a hose.

For a more indepth explanation of this analogy, check out: Crash Course: Electric Charge

1.

## Electric Light

### Incandescent Lights and Light Emitting Diodes

Edison’s incandescent bulb created light by transmitting an electrical current through a filament. As the filament heated up, it glowed, producing light. Today, incandescent lights are being replaced by light emitting diodes (LEDs). LEDs do not heat up in the same way that incandescent lights do, and they are more energy efficient. However, they serve the same purpose in an electrical circuit – to create light.

 PHOTO OF INCANDESCENT LIGHT AND LED LIGHT

An LED has a positive lead and a negative lead. The positive lead is connected to the positive terminal of the battery. The negative lead is connected to the negative terminal of the battery. The positive lead is longer than the negative lead. The rim of the LED is flat on the side with the short lead. This arrangement provides a way to determine the orientation of the LED when the leads are not visible because they have been inserted into a breadboard or socket.

Figure 3. An LED has a positive and a negative lead

## Activity: Light up an LED

For this activity, you will need:

 PHOTO OF BATTERY PHOTO OF WIRE PHOTO OF LED

Using these three components, see if you can make the LED light up with a battery.

### Need help getting it to work?

Place two AA batteries in a battery case similar to the one shown in the illustration below.

Use an alligator clip and connecting wire to connect positive lead of the LED to the positive terminal of the battery. Then connect the negative lead of the LED to the negative lead of the battery. When the circuit is complete, the LED should light up.

Figure 6. A circuit with AA batteries and an LED

Caution. Excessive current can damage an LED. When this occurs the LED can become hot or even explode. Take appropriate safety precautions before proceeding. These can include: (1) wearing safety glasses, (2) placing the LED under a Pyrex container, and (3) allowing the LED to cool off before handling it if it becomes overheated. This is more likely to occur with higher voltages (for example, if using a nine volt battery rather than two AA batteries).

### Diagnosing Problems

Diagnosing and fixing problems is an important part of engineering. If the LED does not light up, you will need to develop a strategy to identify the problem and fix it.

What do you think some of the reasons that an LED might not light up?

Develop a list of some of the causes of the light failing to work. List the potential problems in the order that you believe they are most likely to occur. Then develop a method for determining how to fix the problem.

## Worksheet

### Potential Problems with a Defective Circuit

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1. ________________________________________________

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### Questions

Were you able to light up the LED successfully on your first try? Do you think that inventors like Edison were successful on their first try? Why or why not?

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What did you have to do to make the LED light up?

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What did you learn about circuits in this activity?

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What personal characteristics do successful engineers have to have?

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