Download Using an ammeter

IPS: Unit 2.3 “Using meters”
Name: _________________________
WHAT DO YOU THINK?

What tools do you use to measure distance? ______________________________________________

What information do these tools give you? _______________________________________________

If you have more electricity going into a light bulb what will happen to the light bulb? ____________
_________________________________________________________________________________

What tools could you use to measure how much electricity is going into the bulb? ________________
__________________________________________________________________________________

What do you think these tools are measuring about the electricity? ____________________________
___________________________________________________________________________________
FOR YOU TO DO.
1) Answer the following questions from your Conceptual Physics book or from previous knowledge.
a) Briefly explain the 5 characteristic of a series circuit from section 35.5 in your text.
i) _________________________________________________________________________
ii) _________________________________________________________________________
iii) _________________________________________________________________________
iv) _________________________________________________________________________
v) _________________________________________________________________________
b) What is current? _______________________________________________________________
c) What is the unit for current ,section 34.2? ___________________________________________
d) When current is being measured, what is it actually measuring? Put this in your own words, section
34.2. __________________________________________________________________________
__________________________________________________________________________________
e) What device, tool, do we use to measure current? ___________________
f) What is the symbol for current? ____________________
g) What is the symbol for ampere? ____________________
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Using an ammeter
An ammeter is an electrical device used to measure the amount of current that flows through a wire. An
ammeter is wired in series with the rest of the circuit. To measure the current going through a given wire
you have to break the circuit and insert the ammeter so that all current goes through the ammeter and then
the rest of the circuit. The ammeter has two terminals, one black and one red. The black terminal is placed
in the circuit so that the wire connected to it is closest to the negative terminal of the battery. Closest is
decided by following the wire directly from the black terminal through any other devices like light bulbs to
the negative terminal of the battery. The red terminal is wired closest (along the wires) to the positive
terminal of the battery.
1. Go to http://phet.colorado.edu/
OR:
2. Google: phet circuits dc only
3. Click on the first site.
2) Set up the above circuit in your simulation. As you see the ammeter is located before the light bulb.
Measure the current flowing through the circuit before the current flows through the bulb.
I = ______amps
3) Now the current is measured after it flows through the light bulb. I = ________amps.
4) What does this mean about the current before and after the bulb? ____________________________.
5) If we added more light bulbs to the circuit do you think the current will be the same everywhere or will
it change after each bulb? _______. Why? _________________________________________________
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6) Lets try it. Make the following circuit and measure the current at the four locations. You can use the
non-contact ammeter for this part.
7) What did you notice about the current at each spot? ___________________________
8) Complete the following statement. “ In a series circuit the current ______________________________
________________________________________________ no mater where the current is measured.”
9) Now lets look at the current in a different way. Does the current flowing through the circuit change when
we add more bulbs?
i) What was the current when there was one bulb? ________________
ii) What is it if there are two bulbs? ___________
iii) What is it when there are 3 bulbs? ______________
10) What happens to the current when we add more bulbs? ______________________
11) Why do you think this happens, (think resistance)? __________________________________________
______________________________________________________________________________________
12) Complete the following statement: “As more bulbs are added to a series circuit ___________________
_____________________________________________________________________________________.
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Using a voltmeter
1) Read sections 33.4, 33.5, 34.3, 34.10 (PLEASE read thoroughly) in your conceptual physics text book
then answer the following questions from your Conceptual Physics book or from previous knowledge.
i) What is electric potential energy? _________________________________________________
_______________________________________________________________________________
ii) What is electric potential? _______________________________________________________
iii) What is another name for electric potential? ________________
iv) What is the unit for voltage? ______________
v) What is the symbol for voltage? ____________
vi) A voltmeter doesn’t measure voltage (electric potential), it measures electric potential
difference, also called voltage gain or voltage drop. What is meant electric potential difference?
_____________________________________________________________________________
vii) How does a voltmeter calculate the electric potential difference across a load or source? ______
_____________________________________________________________________________
For you to do, again:
Go to the circuit simulation web site
1. Go to http://phet.colorado.edu/
OR:
2. Google: phet circuits dc only
3. Click on the first site.
We are now going to add a voltmeter to the circuit, leaving the ammeter in place. A voltmeter is an
electrical device used to measure the potential difference (potential drop or gain) between any two points in
a circuit. A voltmeter is wired in parallel with the device that you want to measure the voltage across. To
measure the voltage between any two points in the circuit you touch one terminal of the voltmeter to one
point and the other terminal to the other point. The voltmeter has two terminals, one black and one or more
red. The black terminal is placed in the circuit so that the wire connected to it is closest to the negative
terminal of the battery. The red terminal is wired closest to the positive terminal of the battery. This is
done as illustrated at the right.
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Measure the current passing through the circuit (I) Measure the voltage loss across the light bulb and the
voltage gain across the battery. You do not need 2 voltmeters. You will measure the voltage from one, the
measure the other after that.
a. Current I = ________
b. Voltage gain of the battery V = ________
c. Voltage loss of the light bulb V = ________
d. How do these two values compare, are they relatively close in value or way off? ______________
Two bulbs in series
Wire the circuit shown below with two light bulbs in series.
a. Voltage gain of the battery V= _________
b. Voltage loss of the light bulb #1 V = __________
c. Voltage loss of the light bulb #2 V = ________
d. How does the voltage gain from the battery compare to
the sum of the voltage losses across the bulbs? ___________
e. Explain why you think they are the same. _____________
________________________________________________
f. As compared to the circuit with only one bulb are the
bulbs brighter or dimmer? _________
g. Why do you think the number of bulbs affects the
brightness? ______________________________________
________________________________________________
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Two bulbs wired in series and two batteries in series.
Wire the circuit shown below with two light bulbs in series and two batteries in series.
a. Voltage gain of the battery V= _________
b. Voltage loss of the light bulb #1 V = __________
c. Voltage loss of the light bulb #2 V = ________
d. How does the voltage gain from the battery compare to
the sum of the voltage losses across the bulbs? ___________
e. Explain why you think they are the same. _____________
________________________________________________
f. As compared to the circuit with only one battery and 2
bulbs are the bulbs brighter or dimmer? _________
g. Why do you think the number of batteries bulbs affects
the brightness? ___________________________________
________________________________________________
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