Lab update

Draft due Friday (A) and Monday (F).


Lab calculations

You've (ideally) finished the calculations for the series part of the experiment:

total resistance
percent difference from the theoretical (65 ohms)

If you haven't yet done the parallel calculations, do them:

- total experimental resistance (battery voltage divided by battery current)
- total theoretical resistance - use this formula:
   1/Rp = 1/R1 + 1/R2

The easiest way to proceed is to use the x^-1 key on your calculator.  Don't forget to take the inverse of the sum of the inverses.

- percent difference between theoretical resistance and experimental resistance

Keep working on lab.  You'll still need the usual things:

title
purpose
data table(s)
calculations
conclusion (use the lab questions as a 'jumping off' point - make sure you answer the questions in bold)
sources of error, ways to improve, etc.

HW

In addition to working on the lab, here are circuit questions to think about (A block - Wednesday; F-block - Thursday):

1.  Consider 3 resistors in series with a 12-V battery, with resistances equal to 1, 2 and 3 ohms.  Find the following:

a.  total resistance
b.  current from battery
c.  current through each resistor
d.  voltage over each resistor

2.  Consider 3 resistors in parallel with a 12-V battery, with resistances equal to 1, 2 and 3 ohms.  Find the following:

a.  total resistance
b.  current from battery
c.  current through each resistor
d.  voltage over each resistor

3.  Imagine if you had a circuit with a 12-V battery in series with a 4-ohm resistor - and this is in series with a parallel combination of resistors (3 and 6 ohms).  How would you treat this circuit, if you wanted to determine the total resistance, and all currents and voltages?  Give this a shot, if you have time.

Lab writeup questions

Folks,

You have some data for a series circuit and a parallel circuit.  I will give you some "leading questions" to help you frame your formulation of Kirchoff's Rules.  The questions in bold are to be answered in your lab report.

I.  Series Circuit

Think about these things: 

- What do you find to be true about the voltages?  

- What do you find to be true about the currents?  

- How do the individual voltages compare to the battery voltage?

- How do the individual currents compare to the battery current?

Write a general rule about voltages in a series circuit.

Write a general rule about currents in a series circuit.

Calculations (you may have to wait until next class for these):

What is the total resistance of this circuit (according to the values of the resistors given in class from the stripes)?

What is the total resistance of this circuit according to calculation?  (R = battery voltage divided by battery current)

II.  Parallel Circuit

- What do you find to be true about the voltages?

- What do you find to be true about the currents?  

- How do the individual voltages compare to the battery voltage?

- How do the individual currents compare to the battery current?

Write a general rule about voltages in a parallel circuit.

Write a general rule about currents in a parallel circuit.

Calculations (you may have to wait until next class for these):

What is the total resistance of this circuit (according to the values of the resistors given in class from the stripes)?

What is the total resistance of this circuit according to calculation?  (R = battery voltage divided by battery current)

Other general questions to answer:

Did you notice if resistors got hot?  Why might this be?

What exactly is Ohm's Law?  Does it apply to all electrical components?

What do you think "tolerance" is, as applied to resistors.  For example, if a resistor is said to have a 10% tolerance, what can that mean?

Give sources of error in this experiment.

A block HW

Graph your lab data:

I vs. R

That is, I (on the y-axis) vs. R (on the x-axis).

What do you make of this relationship?  Does it make sense in light of the definition of resistance?

Also, draw an electrical schematic for your circuit, using the symbols for battery, resistance and wire.  You may have to look up the symbols online.

Also, try the F-block problems posted earlier, if you have time.

HW for F-block

Please review definitions of voltage, current, and resistance (along with their units).

1.  How long would it take a circuit carrying 4 amps to pass 50 coulombs of charge?

2.  A 9-V battery is attached to a resistor.  As a result, 0.1-A of current passes through it.  What is the resistance of the resistor?

3.  Look up the schematic symbols for battery, wire and resistor.  Draw a basic circuit which depicts the bulb and battery arrangement we made in class.

For next class (Friday and Monday)

Find definitions for:

- current 

- resistance

Thank you.

HW

Come to class with a definition of energy that is better than my "blocks" analogy.