From the Blog Manager

Dear readers,

It has certainly been a while since I updated a new science experiment.

I came back to Woodbury, Minnesota for my senior year in highschool.

Ever since I came back to the United States, I have not been able to care for my blog for a while because of school work, extracurricular activies, and college applications.

To concentrate more on school and college applications, I have decided to take a break on running the blog.

I will actively update more experiments and articles after I enter College.

I am terribly sorry for notifying you readers about the delay with such a late notice.

Thank you so much for giving care and support.

I will return as soon as possible with more interesting and fun homemade experiments.

Thank you

Predicting the Working Temperature of the Light Bulb's Filament

What is the temperature of light bulb?
(by Daniel Lee and Shin Lee)

There is a relationship between the resistance of the material and its temperature.
We call this Temperature-resistance relation of the material.
For metal, the resistance increases when its temperature rises.
It can be indicated as follows;

R=R0(1+αT)

It says if we know the resistance, we can calculate the temperature of the wire.
Similarly, if we know the (temperature of the wire), we can calculate the (resistence) of the material.

Alpha=temperature resistance coefficient
0.0039 for most metal

1)What is the room resistance of the bulb (4.2)ohm
2)What is the room temperature? (25)oC
3)Then, what is the Ro from the above equation? (4.057 )

Turn on the cold small lightbulb using the batteries and aligator clips for about a couple of minutes.
Then read the current using the DMM(Digital Multi-Meter) as shown below:

From the previous lab journal, The DMM(Digital Multi-Meter) is a Stethoscope for Electric Circuit, we can get the values below.

1)resistance of the hot bulb? (108.47ohm)
2)the temperature of the hot bulb?
108.47=4.057(1+0.0039T)
0.0039T=108.47-4.057=104.413
Therefore, T=104.413/0.0039=26772.5641 Degrees Celcius=27045 Kelvin.

It is well known that the sun's temperature is 5777 Kelvin.
The sun, obviously, is the hottest thing that exists in our solar system.

Is this calculation right?

Reading Resistance with Color Codes.

Tools: Digital Multi-Meter, Registers with Color Code.

Measuring Resistance

How to read the resistance from the DMM.

If you wish to measure the registance accurately, make sure to hold the register tightly with the probe.

How to read the resistence by the color code on the surface of registers.

Colors' Values
Brown 1
Red 2
Orange 3
Yellow 4
Green 5
Blue 6
Purple 7
Gray 8
White 9
Black 0
Gold 5% error
Silver 10% error

For example:

A register that has color codes of brown, black, red, gold can be measured as follows:

1) (brown, black, red, gold)=102(5%)=10*102(5%)=1000 ohm
(5%) error indicates that the resistance is greater than 950ohm but less than 1050ohm.

Second Example which was shown in the photo above can be calculated through:

(orange, orange, brown, gold)=330(5%)=33*101(5%)=330 ohm
(5%) error indicates that the resistance is greater than 313.5ohm but less than 346.5ohm.

The value from the DMM, 333.7ohm, satisfies the range shown above on the 2nd example.

The DMM (Digital Multi-Meter) is a Stethoscope for Electric Circuit.

Caution: Be careful for the safety! Electricity is very dangerous and very hot sometimes, so you may burn your finger!

Tools: Digital Multi-Meter, Battery, Battery Holder, Socket, Light Bulb, Aligator Clip, LED

It can be used in different ways.

Here are typical examples of how to use DMM.

(1) Measuring dc voltage

I made two 3.2V DC with four 1.6V DC battery with two holders.
I only thought that batteries were only 1.5V. However, when measured, the instrument shows 1.6V.
The series connection of the two 1.6V batteries creates 3.2V.

(2) Measuring ac voltage

AC indoor power line in Korea has 225.3V
Koreans normally call the power line’s voltage 220V. However, it is actually 5.3V higher.
Compared to the American power line, Korean power line is more lethal.

(3) Measuring dc current

The indicator shows that the current flowing through the small light bulb is 29.5mA.
The supplying voltage is 3.2V.
The (working) resistance can be calculated with Ohm’s law.
V=iR.; 3.2V=29.5mA*R
R=3.2V/29.5mA=3.2V/0.0295A=108.47
The room resistance was 4.2ohm at 25oC.

(4) Measuring temperature

Digital Multi-Meter can be also used as a Thermometer.
I positioned the temperature probe between my armpits.
It says that my body temperature is 37oC.
There could have been an error because a cloth blocking my body and the probe.

My profile

It seems that I have not introduced myself fully.

I am currently a foreign student who is studying in Minnesota in New Life Academy.

I had many influence in science from my father who is a Professor in Mechanical Engineering.

After I learned interesting concepts of physics and basic scientific knowledge, I decided to share several of experiences on a blog.

I wanted to create a blog that anyone could use and perform.

Therefore, I mainly did experiments that can be done with typical things that can be found at home.

I sure hope that people would be able to step closer to the world of science!

P.S. After reading the reports that I have uploaded, you might have a confusion because of complicated physics theory or my english.

You can ask questions or parts needing clarification to my e-mail.

My email is chungjae12@yahoo.com

I will respond to your e-mail ASAP.

What is the difference between the heat transfer in the air and in the water?

I am terribly sorry for the late update.

It was my father's birthday.
We went the Baskin' Robbins 31 to order a bucket of ice cream.
Inside the bag, we found some solid carbon dioxide.
Such material sparked our curiosity.
We began our experiment right away.
Tools: Solid Carbon Dioxide, Cup, Water, Spoon

Procedure:
1. Get a cup of water and a spoon.
2. Add a block of solid carbon dioxide into the water.
3. Observe the evaporation.

Discussion:
What is the difference between the sublimation with water and the sublimation with air?
The sublimation in the water is very vigorous or strong compared to the sublimation in the air.
The sublimation in the air can be regarded as a heat transfer from the solid to gas.
However, the evaporation in the water can be regarded as a heat transfer from the solid to liquid.

The molecular density of in the air is less dense than that of the molecular density in the water. Here, the molecules can be regarded as a media for heat transfer.

I heard that the above heat transfer called as a convection heat transfer among 3 modes of heat transfer, conduction, convection and radiation.

Can you imagine yourself in a public bathtub?
If you see the thermometer in the Sauna room, it would be 80 deg Celsius or 170F.
However, you can endure the heat of the water.
This time, imagine yourself in a tub of water with temperature of 80 deg Celsius or 170F, (This condition is really dangerous, really dangerous so that you may be killed or hurt. It is really dangerous)

What is the difference between the two phenomena above?
The first one is similar with the situation the dry ice in the air and the second one is similar with the dry ice in the water.

Extra Experiment:
Can you make Sprite at home?

Tools: Previous Mixture, Sugar

Procedure:
1. Add a proper amount of sugar to the previously created mixture of solid carbon dioxide with water. 2. Take a little sip to the chemical. (The origin and the usage of the solid carbon dioxide was unknown. There are possibilities of it being poisonous.)

It did not taste as good as commercial Sprite at Wal-mart!

Acceleration of the Elevator Box

People tend to call me overweight.

To change the stereotype, I decided to change my weight in a short time.

Realizing that healthy diet and daily excercise takes several month, I searched for quicker way of changing my weight.

Tools: Bodyweight Scale, Elevator

Introduction:

Weight in scientifical definition is a force exerted on an object by gravity.

I decided to see the variation of weight through difference in gravity.

Procedure:

1. Find a nearby elevator.

2. Go to the highest level.

3. Go on the bodyweight scale and measure the actual weight.

4. As the elevator goes down, observe the change of weight.

Observation:

My weight is 80kg. (80kg-g is more correct or accurate expression instead of 80kg. 80kg is the mass of my body, however 80kg-g is the weight of my body, that is the force that the gravity makes.)

When the eleator went down it pointed at 75kg.

When I pushed the first floor button at the twentieth floor, the scale indicated at 75kg for the first three floors.

The reason for the sequence is stabilization.

During the first three floors, acceleration of the elevator occured from zero to 5m/s.

However, after the first three floors, the elevator moved at a constant speed at 5m/s.

(Constant velocity means no acceleration or addition of force. However, acceleration indicates that there was an additional force affecting our body.)

Conclusion:

We can apply the Newton's Second Law to this experiment.

Summation of the external forces is equivalent to inertia force: F=ma.

(g=gravity, a=acceleration, 75g=measured value of weight during down of elevator, 80g=weight of my body at initial state, 80a=inertia force of my body)

75g-80g=80a

-5g=80a

therefore, a=-0.613m/s^2

a is the acceleration of the elevator.