Understanding how a light bulb functions - Studyladder Interactive ... - Free Printable

Let's go through each part of the worksheet and solve it step by step, explaining the concepts clearly.

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1. Draw a simple circuit that will light a low voltage light bulb (lamp).

Answer:
To draw a simple circuit, you need to use the symbols provided:

- Cell (battery): `| |`
- Wire: straight line
- Switch: zigzag line (open or closed)
- Lamp: circle with an "X" inside

Here’s how the circuit should look:

```
[Cell] ———— [Wire] ———— [Switch] ———— [Lamp] ———— [Wire] ———— back to cell
```

In diagram form:

```
+———| |———|———|———○———|———+
| | | | | |
| | | | | |
+———————+———————+———————+
```

But using standard symbols:

```
┌─────┐ ┌──────┐ ┌────────┐
│ │ │ │ │ │
│ + │──────│ S │──────│ L │
│ - │ │ │ │ │
└─────┘ └──────┘ └────────┘
│ │ │
└───────────────┴─────────────┘
```

Where:
- `+` and `-` = battery (cell)
- `S` = switch
- `L` = lamp (light bulb)

✔ Explanation: A complete circuit must have a power source (cell), wires to carry current, a switch to control the flow, and a load (the lamp). When the switch is closed, current flows and lights the bulb.

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2. Which parts of the light bulb need to connect to the wires to complete a simple circuit?

Answer:
The metal base and the side contact (screw thread) of the bulb must connect to the wires.

- The bottom metal tip connects to one wire.
- The metal screw thread (side) connects to the other wire.

These two points are connected internally to the filament, completing the path for electricity.

✔ Why? The filament is the thin wire inside the bulb that heats up and glows when current passes through it. The circuit must be continuous from the battery, through the wires, into the bulb via both contacts, through the filament, and back.

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3. What do you think these parts are made of?

Answer:
- Filament: Made of tungsten – a metal that can withstand very high temperatures without melting.
- Glass bulb: Made of glass – to protect the filament from air (prevents oxidation).
- Metal base and screw thread: Made of copper or brass – good conductors of electricity.
- Support wires: Usually molybdenum or tungsten – strong metals that resist heat.
- Gas inside: Inert gases like argon or nitrogen – prevent the filament from burning out.

✔ Why? These materials are chosen for their electrical conductivity, heat resistance, and ability to keep the filament intact during operation.

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4. What happens to the filament in an incandescent lamp when the switch is turned on?

Answer:
When the switch is turned on, electric current flows through the filament. Because the filament has high resistance, it heats up rapidly to about 2,500°C. At this temperature, it glows white-hot, producing visible light.

✔ This process is called incandescence – light produced by heat.

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5. How does a compact fluorescent lamp produce light?

Answer:
A compact fluorescent lamp (CFL) produces light differently:

1. Electricity flows through a gas (usually mercury vapor) inside the tube.
2. This causes the gas to emit ultraviolet (UV) light.
3. The UV light hits a phosphor coating on the inside of the glass tube.
4. The phosphor converts UV light into visible light.

✔ This is more efficient than incandescent bulbs because less energy is wasted as heat.

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6. Incandescent bulbs are not as efficient as compact fluorescent lights. Why?

Answer:
Incandescent bulbs waste a lot of energy as heat. Only about 10% of the energy goes into making light; the rest is lost as heat.

Compact fluorescent lamps (CFLs) are more efficient because:
- They produce light using fluorescence, not heat.
- They convert more electricity into visible light.
- They use less power to produce the same amount of light.

✔ So, CFLs save energy and last longer than incandescent bulbs.

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✔ Final Summary of Answers:

| Question | Answer |
|--------|--------|
| Draw a circuit | Use cell → wire → switch → lamp → wire → back to cell. |
| Which parts of bulb connect? | Bottom tip and side screw thread. |
| What are the parts made of? | Filament: tungsten; Base: copper/brass; Bulb: glass; Gas: argon/nitrogen. |
| What happens to filament? | Heats up and glows due to electrical resistance. |
| How does CFL work? | UV light from gas excites phosphor coating → emits visible light. |
| Why less efficient? | Incandescent bulbs waste energy as heat; CFLs convert more energy into light. |

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