hw for Friday

Hi everyone, and thanks for getting your labs done!

For Friday, investigate these things:

electromagnet

the right-hand rule (for magnetic fields around current-carrying wires) - this may be tricky to understand.  It is a rule which helps you remember what the magnetic field looks like around a wire (with current in it).

motor (the basics) - if time permits

circuit stuff

HW

Try the combination circuit problem on the hand-out.  Hints:

1.  Figure out the total resistance first, which you'll do by finding out what is in series and what is in parallel.  Then find the total resistance.

2.  Next, find the total/battery current.

3.  Then, make a chart and do your best to fill it in, figuring out which (if any) currents equal the total/battery current.


Also, lab draft due next class.  The final lab report will be due 2 classes after that.


Additional circuit problem, if you would like to try it:

You have three resistors:  30, 40 and 60 ohms.  Find the total resistance, all currents and all voltages if they are:
a.  in series
b.  in parallel

Lab questions

Lab Questions for Ohm's Law lab

So far, you've done 2 graphs: I vs. R, V vs. R. They will be included in your lab. Don't forget titles, units, etc.

Lab questions

1. Examine the 2 graphs. Do they make sense? Why? What's going on in them? Do they appear to obey any mathematical relationship/equation?   Is one graph stranger (or more unexpected) than the other?  Discuss.

2.  Calculate experimental resistances for each pair of V and I - use the equation R = V/I

3. You've just determined experimental resistances for each trial. Are they within 10% of the expected/theoretical values (the ones on the box)? Should they be? If not, why are they not so good?  Don't forget sources of error, in general.

4. What does it mean exactly if something follows Ohm's Law? Do all electrical devices follow this law? Are there substances that definitely are not "ohm-ic"?

5. Other than the batteries "dying," what might happen as the batteries are connected to the resistors? Would the V and I values change?

6. What is meant by "internal resistance" of the battery, and how does it affect this experiment (your results)?

7. In part 2 of the experiment, you experimented with resistors in series and in parallel.  What can you generally summarize from resistors in series versus being in parallel?

8. Anything else you want to conclude or talk about.

9.  Hooray!

FYI

Just some football madness:  I have not fact-checked this.

Jacoby jones ran 108 yards in 11 seconds.

That's an average ground velocity of 9.81+ yards/sec.

This is equivalent to running a 40 yard dash in 4.08s. The fastest 40 time ever recorded in the NFL combine was 4.24.

Jacoby Jones was, in fact, only 1.4s slower down the field than Usain Bolt's world record in the 100m, (110y = 100m). This is before you add in the extra length due to Jacoby not running a straight line.

THAT'S NUTS!!!

HW

Next class, we will begin the formal lab on basic circuits.  To prepare:

1.  Draw a circuit containing the following:  a 3-V battery/source, wire and a resistor.

2.  Learn the difference between electrical devices "in series" and "in parallel."

3.  Try to find out a little about how to use a "multimeter".  How does one measure voltage?  How does one measure current?

In general, the structure of the lab is thus:  you will have a 3-V battery in series with a changing resistor.  You will change the value of the resistor many times.  For each trial, after changing the resistance, you will measure voltage and current.  What do you suppose will happen to:

a.  the voltage
b.  the current

Since you will graph data, what do you suppose the graphs will resemble.

In a pre-lab hypothesis, suggest what you believe will happen to voltage and current as resistance is changed.

You may also wish to set up data tables with headings for resistance, voltage and current.  Don't forget units.

Hooray!

Circuit intro homework

Answer these questions before next Tuesday's class:

1.  What exactly is an electrical circuit.

2. What is voltage (and its units)?

3.  What is current (and its units)?

4.  What is resistance (and its units)?

5.  Draw some electrical symbols (battery, resistor, wire, and others of interest).

6.  How does a battery work (basically)?