Friday 30 Jan:

Key Concept's) Today: Simple machines & forces/stress/strain/compression

Pd 2:

Mini- Lab (no written procedures or material)

just Hypothesis, Data, & Conclusion

Finish structures

Think of ways to gather Data for

Testing on Monday (All Structures):

On Monday, be ready to talk about:

• What type of data can we measure/observe during testing

• Think of how to write a Hypothesis on this activity using the entire class a lab team.

• What would a conclusion look like

W/S: Simple Machines

Lab:  Buoyancy (Monday)  Pd 1

Lab:  Tower (Monday)  Pd 2

   L#38: 1,2, 5-6, 9, 13, 15, 18 (Due Tuesday 1st)

****L #37:   1-4, 7-9, 11-13          (due Wed 3 Feb)

Lab:  Electrical Circuits (Thurs 4 Feb)

L#39: 1- 6, 9, 10, 12, 14, 17, 18 - 20   (due Mon 8 Feb)

L#40: 1-7, 9, 11, 15, 16, 18, 19 (due Wed 10 Feb)

Volt: Potential  (like height & steepness of a hill)

Amp: Current  (like amount of water in a stream or river)

 Resistance (ohms - Ω ):   (like friction - stops the flow of electricity)

Lab:   Circuits     Thurs    4 Feb

Notes: L#39

CHANGING STATES OF MATTER All matter can move from one state to another. It may require very low temperatures or very high pressures, but it can be done. Phase changes happen when certain points are reached. Sometimes a liquid wants to become a solid. Scientists use something called a freezing point to measure when that liquid turns into a solid. There are physical effects that can change the freezing point. Pressure is one of those effects. When the pressure surrounding a substance goes up, the freezing point also goes up. That means it's easier to freeze the substance at higher pressures. When it gets colder, most solids shrink in size. There are a few which expand but most shrink. Now you're a solid. You're a cube of ice sitting on a counter. You dream of becoming liquid water. You need some energy. Atoms in a liquid have more energy than the atoms in a solid. The easiest energy around is probably heat. There is a magic temperature for every substance called the melting point. When a solid reaches the temperature of its melting point it can become a liquid. For water the temperature has to be a little over zero degrees Celsius. If you were salt, sugar, or wood your melting point would be higher than water. The reverse is true if you are a gas. You need to lose some energy from your very excited gas atoms. The easy answer is to lower the surrounding temperature. When the temperature drops, energy will be sucked out of your gas atoms. When you reach the temperature of the condensation point, you become a liquid. If you were the steam of a boiling pot of water and you hit the wall, the wall would be so cool that you would quickly become a liquid. Finally, you're a gas. You say, "Hmmmm. I'd like to become a plasma. They are too cool!" You're already halfway there being a gas. You still need to tear off a bunch of electrons from your atoms. Eventually you'll have bunches of positively and negatively charged particles in almost equal concentrations. When the ions are in equal amounts, the charge of the entire plasma is close to neutral. (A whole bunch of positive particles will cancel out the charge of an equal bunch of negatively charged particles.) A plasma can be made from a gas if a lot of energy is pushed inside. All of this extra energy makes the neutral atoms break apart into positively and negatively charged ions and free electrons. They wind up in a big gaseous ball.

http://www.miamisci.org/af/sln/phases/waterempty.html

Water’s temperature does not change during phase transitions as heat flows into or out of it.

 

Q_s (energy to heat a solid):          (m)(c_s)(DT)

Q_s-L (energy for phase change S-->L):  (m)(H_{Heat of Fusion})

Q_L (energy to heat a liquid):        (m)(c_L)(DT)

Q_s (energy for phase change L-->V):  (m)(H_{Heat of Vaporization})

Q_V(energy to heat a vapor):         (m)(c_V)(DT)

 

Example: How much energy does it take to change 2-kg of Cu from 983⁰C to 1587⁰C   (H_F = 135x10³; H_V = 5,070x10³, c_S = 400, c_L = 500, c_V = 200)

Q_s (energy to heat a solid):          (m)(c_s)(DT)

                                                    (2)(400)(100)  =                          80,000J

Q_s (energy for phase change S-->L):  (m)(H_{Heat of Fusion})

                                                           (2)(135x10³)  =                   270,000J

Q_L (energy to heat a liquid):        (m)(c_L)(DT)

                                                      (2)(500)(104)  =                       104,000J

Q_s (energy for phase change L-->V):  (m)(H_{Heat of Vaporization})

                                                       (2)(5,070x10³)  =               10,140,000J

Q_V(energy to heat a vapor):         (m)(c_V)(DT)

                                                                                   (2)(200)(400)  =                     160,000J

                                                     10,754,000

Lab: Ohm's Law

The fundamental relationship among the three important electrical quantities current, voltage, and resistance was discovered by Georg Simon Ohm.. In this experiment you will see if Ohm’s law is applicable to several different circuits using a Current Probe and a Voltage Probe.

Current and voltage cannot be observed directly. To clarify these terms, some people make the comparison between electrical circuits and water flowing in pipes. Here is a chart of the three electrical units we will study in this experiment.

Figure 1

                                                Black wire                       

Red wire                         +                  - 

                                                                                                         (Red side)             (Black side)

                                                                                                                Amps Probe (in line)

                                      (on both sides of resistor)

Questions

·   What is the mathematical relationship between current, potential difference, and resistance in a simple circuit?

MATERIALS

Hypothesis:

1. If the electrical potential is increased, then the current through normal 10 W resistor

(decreases, remains constant, or increases) proportionally  because ….

2. If the electrical potential is increased, then the current through light bulb (decreases, remains constant, or increases) proportionally because…

Pre-Lab & PRELIMINARY Questions:

1. Using just one wire, one 6.3 V light bulb  and one 6.0 V battery draw the four different ways that you can light a bulb.

2. Make a diagram of how the electricity flows from one end of the battery through the battery, through the wire, through the bulb and back to the starting point.

3. Does it matter in which direction the current flows to make the bulb light? Explain why or why not.

PRELIMINARY SEtup:

1.   Connect the Current Probe to Channel 1 and the Differential Voltage Probe to Channel 2 of the computer interface.

2.   Open the file “25 Ohms Law” in the Physics with Computers folder. A graph of potential vs. current will be displayed.

3.   With the power supply turned off, connect the power supply, 10 W resistor, wires, and clips as shown in Figure 1. Take care that the positive lead from the power supply and the red terminal from the Current & Voltage Probe are connected as shown in Figure 1. Note: Attach the red connectors electrically closer to the positive side of the power supply.

4.   Click . A dialog box will appear. Click  to zero both sensors. This sets the zero for both probes with no current flowing and with no voltage applied.

5. IMPORTANT! Turn the control on the DC power supply to 0 Volt. However, turn the “Current” Knob (AMP) slightly to the right (about 1/10 of a turn), so that the “red light” (“Limited Current”) is off. 

6.   Have your teacher check the set-up arrangement before proceeding.

PROCEDURE

1.   Record the value of the resistor in the data table.

Condition #1 (10 W resistor):

2.   Turn on the power supply. Click  to begin data collection, then slowly increase the voltage and amperage to 1 Volts and 1 AMPs. When the readings are stable click .

3. Read Carefully: Now slowly increase the voltage (and amperage as needed) to 2.0V,  2.5V 3.0V,  4.0V, and finally to 5.0 V.  Monitor the voltage and current and click  at each assigned interval (2V, 2.5V, 3V etc.).

4..  Click  and set the power supply back to 0 V.

5.  Print a copy of the graph. Are the voltage and current proportional? Click the Linear Fit button, . Record the best fit line & the Y-intercept of regression line (V)

Condition #2 (51 W resistor):

6.   Reconnect the power supply, 51W resistor, wires, and clips as shown in Figure 1

7. Repeat Steps 1 – 5 using the 51 W resistor.

Condition #3 (6.3 V light bulb - round one):

8.   Reconnect the power supply, 6.3 V light bulb - round one, wires, and clips as shown in Figure 1, replacing the 51 W resistor in the circuit with a 6.3 V light bulb (round one).

9. a. Now slowly increase the voltage (and amperage as needed) from 0.0V to  0.5 V,  1.0V, 1.5V,  2.0V, 2.5V, 3.0V, 3.5V, 4.0V, 4.5V and finally to 5.0 V.  Note: do not exceed 5.0 V. otherwise the bulb may burn out.

      b. Note the brightness of the bulb in relationship with voltage and current.

10. Click  and set the power supply back to 0 V.

11. For Condition #3: Compare slopes of data at different parts of the curve, first click and drag the mouse over the first 3 data points. Click the Linear Fit button, , and record the slope of the regression line in the data table.

12.   Click and drag the mouse over the last 7 points on the graph. Click the Linear Fit button, , and record the slope of the regression line in the data table.

Condition #4 (2.5 V light bulb - thin one):

13. Reconnect the power supply, 2.5 V light bulb (thin one), wires, and clips as shown in Fig 1, replacing the 6.3 V light bulb in the circuit with a 2.5 V light bulb (thin one).

14. Now slowly increase the voltage (and amperage as needed) to 0.0V, 0.5 V,  1.0V, 1.5V,  2.0V, 2.5V and finally to 3.0 V.  (ONLY GO TO 3.0V). Note: do not exceed 3.0 V, otherwise the bulb may burn out.

15. Monitor the voltage and current and click  at each assigned interval (0.5V, 1.0V, 1.5V etc.).

16. Click  and set the power supply back to 0 V.

17. For Condition #4: Compare slopes of data at different parts of the curve, first click and drag the mouse over the first 3 data points. Click the Linear Fit button, , and record the slope of the regression line in the data table.

18.   Click and drag the mouse over the last 4 points on the graph. Click the Linear Fit button, , and record the slope of the regression line in the data table.

DATA TABLE

Conclusion:  (your own)

ANALYSIS:

1. a. If the voltage doubles, what happens to the current?

b. As the potential (Volts) across the resistor increased, the current (Amps) through the resistor increased. If the change in current is proportional to the voltage, the data should be in a straight line and it should go through zero. In these two examples how close is the y-intercept to zero? Is there a proportional relationship between voltage and current when the resistance is constant?

2. Compare the slopes in each of the above equations to the resistance of each resistor. How does the amount of resistance (Ohms) effect the slope? What does this mean?

3. Do your resistors follow Ohm’s law? (Base your answer on your experimental data.)

4. a. By observing the light bulb directly, how do you know the relative amount of current (Amps) that is going through the bulb?

b. The slope of the linear regression line is a measure of resistance. Was the change (slope) linear? Describe what happened to the amount of current (Amps) that passes through the light bulb as the potential (voltage) increased.

c. Describe what happened to the amount of resistance of a light bulb as the voltage increased.

d. Why do you think causes this change in resistance to the amount of current passing through a light bulb?

5. a. Does your resistors follow Ohm’s law? Explain.

    b. Does your light bulb follow Ohm’s law? Explain.