Experiment 9
We explored the difference between incandescent mini bulbs and LED bulbs. The incandescent types use up a great deal more energy. In this experiment we will determine how much of that energy is lost to heat.
What would you predict? 10%, 20 %, 50% of the energy lost to heat? Let's find out.
STEP 1. We will need a small container of water. It would be best to do this in a styrofoam cup. (Yes, awful, but the only really good use of an insulated cup!). A regular small glass that is surrounded by some sort of insulation would also work. The idea is that we will be generating some heat and we don't want any to be lost!
STEP 2. Carefully measure 1/4 cup of room temperature water into the cup. If you have a graduated cylinder, then measure out 59 milliliters. (1/4 cup is about equal to 59 ml)
Allow the water to stand in the insulated cup until it has reached room temperature. Place thermometer in the water and carefully record the starting temperature.
STARTING TEMPERATURE____20 Degrees C______
WATER VOLUME 59 Milliliters
STEP 3. While you are waiting for the water and thermometer to stabilize (equilibrate), arrange a bulb and a cell so that it has long wires attached. If you have a multimeter, you can measure the exact voltage and the current in the circuit. Otherwise you can assume your bulb is like most mini bulbs and the following would be true:
The voltmeter is placed The ammeter is placed in the circuit so it can
across the mini bulb. measure rate of flow.
VOLTAGE APPLIED: 2.32 Volts
CURRENT FLOW (RATE): .210 Amperes
STEP 4. Place the bulb in the water so that just the glass is submerged. There are no shock hazards here, so if you do get the wires wet it will not harm anything.
NOTE THE STARTING TIME: __2:04_________
STEP 5. Allow the lit bulb to stay in the water. Place some insulation on top. I put a piece of packing foam on top to keep all the heat in. The excess heat from the bulb will heat the water. Have you ever noticed how mini bulbs melt the snow around them in winter?
Every minute gently swirl the water so it mixes the warmed area with all of the liquid.
STEP 6. Allow this to heat for 30 minutes.
NOTE THE ENDING TIME: ___2:34________
Carefully read the thermometer and record the final temperature.
FINAL TEMPERATURE:___22.5 degrees C___________
STEP 7. Now let's do some calculations. Let's first compute how much electricity our system used.
Watt Hours = watts X hours
= Amperes X Voltage X minutes/60
=0.21 X 2.32 X 30/60
= .24 Watt hours
STEP 8. How much heat did the water absorb?
Initial Temperature: 20 degrees C
Final Temperature: 22.5 degrees C
Change in temperature 2.5 degrees C
The number of calories in heat that the water absorbed = Change in Temperature C X Number of milliliters of water
Calories = 2.5 degrees X 59 ml
Calories = 147.5 calories
STEP 9. Energy in >>. Energy out. So, in my example we used up .24 Watts of electrical power
The water absorbed 147 Calories. So how much is that in watts? A watt is equal to 860 calories.
Therefore, our 147.5 Calories is 147.5/860 watts. That is .18 Watts. This would mean the .18 out watts /.24 in watts showed that 75% of the energy went into heat. We can presume that the rest was lost or created light.
Discussion: Incandescent bulbs transfer more electrical energy into heat than light! Reference sources say that an incandescent bulb produces 90% in heat. (That is more than our experiment found!) If you have ever tried to remove a regular light bulb after it has been on a while, you will notice it is hot! Remember that the way incandescent lamps function is by heating the filament. It must get hot to "burn" electrons out of their orbits. One thing you can do with different kinds of lamps is create a heat source. Many incubators and some small ovens use lamps to generate heat.
