Energy Transfers in Light Bulbs: More Than Just a Glow
GCSE & A-Level Physics with Hemel Private Tuition
#GCSEPhysics #ALevelPhysics #EnergyTransfers #PracticalPhysics #HemelPrivateTuition
When students think of energy transfers in a light bulb, they usually stop at, “It gets hot and makes light.”
But at Hemel Private Tuition, we like to dig a little deeper—because behind every glowing filament or LED lies a brilliant mix of physics concepts just waiting to be explored.
This week’s focus in the lab? Energy transfers in electric lighting—and how we can observe, measure, and make sense of them.
⚡ What Happens in a Light Bulb?
Let’s take a classic filament bulb:
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Electrical energy flows into the bulb.
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The thin tungsten filament resists the current.
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This resistance causes it to heat up (thermal energy).
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The hot filament emits visible light and infrared radiation.
So, the energy transfer chain is:
Electrical → Thermal → Light (and heat loss)
With a modern LED, it's a little different:
Electrical → Light (with much less thermal loss)
Why Does the Filament Glow in a Light Bulb?
The filament in a traditional incandescent light bulb glows because of a process called incandescence—which is just a fancy word for “glowing due to heat.”
Here’s what happens:
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Electric current flows through the filament (usually made of tungsten). This current is made up of electrons moving through the metal.
Now, tungsten has a high resistance, which means it doesn’t let electrons flow through it easily.
As the electrons move, they collide with the atoms in the tungsten over and over again. These collisions transfer energy from the moving electrons to the tungsten atoms.
As a result, the tungsten atoms vibrate more and more, and this increase in atomic motion is what we experience as heat (thermal energy).
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The filament heats up to around 2,500 to 3,000°C.
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At these temperatures, the tungsten emits visible light—starting with red, then orange, yellow, and eventually white as the temperature increases.
This is the same principle as heating a piece of metal in a fire—it starts to glow as it gets hotter.
🔬 Why Tungsten?
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Very high melting point (~3,422°C), so it can withstand the heat without melting.
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Durable and strong, even when very thin.
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Emits a broad spectrum of light that’s quite similar to natural sunlight.
💭 Bonus Thought:
Only about 5–10% of the energy used in a filament bulb becomes visible light. The rest is lost as infrared radiation (heat)—which is why they’re being phased out in favour of LEDs, which are much more efficient.
🧪 Experiments We Use to Explore This
🔍 1. Thermal Imaging of Bulbs
Using a thermal camera or IR thermometer, we compare the surface temperatures of:
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A filament bulb
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A compact fluorescent lamp (CFL)
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A modern LED
Observation: Filament bulbs waste a lot of energy as heat. LEDs stay cooler = more efficient.
⚖️ 2. Using a Joulemeter or Energy Logger
We connect bulbs to an energy logger or a smart plug with a power monitor and measure:
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Input energy (in joules or watt-hours)
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Brightness output (subjectively or using a light sensor)
Extension: Compare energy usage for the same light output.
💡 3. Luminance vs. Power Graphs
We use a light sensor and variable resistor to test how changing the input voltage affects brightness. A great experiment for A-Level students to connect circuits with energy transfer efficiency.
🌡️ 4. Heat Transfer from a Bulb
Place a bulb near a container of water or a temperature sensor. Turn on for a set time and observe the temperature rise.
Link: Conservation of energy – energy isn’t lost, just transferred to surroundings.
🎓 Teaching Points
For GCSE:
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Energy transfers: Sankey diagrams
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Wasted energy vs. useful energy
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Efficiency calculations
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Comparison of different bulb types
For A-Level:
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Internal resistance
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Power = IV = I²R
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Energy efficiency and rate of transfer
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Thermodynamics and blackbody radiation
💬 Why It Matters
In an age of energy-conscious design, understanding how devices use and lose energy is essential. From sustainability to electronics, it’s not just about making things work—it’s about making them work better.
And what better place to start than the humble light bulb?
At Hemel Private Tuition, we turn everyday objects into powerful physics lessons.
With live demonstrations, thermal cameras, and data loggers, our students don’t just learn the equations—they see them in action.
📍 Book a 1:1 session online or in our fully equipped classroom and lab.
#GCSEPhysics #ALevelPhysics #PhysicsExperiments #EnergyTransfers #LightBulbsExplained #PracticalPhysics #HemelPrivateTuition #STEMLearning #PhysicsIsEverywhere
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