Resistance of a Wire - GCSE Science Required Practical
Summary
TLDRThis script outlines an experiment to study how resistance in a wire varies with its length using a high-resistance nichrome wire. The setup involves a series circuit with a battery, ammeter, and voltmeter. Measurements are taken from 100 cm to 30 cm, calculating resistance using Ohm's law. The goal is to plot resistance against length and observe the relationship, ensuring the circuit is disconnected between readings to prevent wire heating that could alter resistance.
Takeaways
- 🔬 The experiment investigates the relationship between the resistance of a wire and its length, using a nichrome wire due to its higher resistance compared to copper.
- 📏 A meter-long nichrome wire is used, measured against a ruler for precise length determination during the experiment.
- 🔌 The setup includes a series circuit with a battery, ammeter, and the resistance wire, ensuring both current and potential difference can be measured.
- 🔋 The voltmeter is connected in parallel to the resistance wire to measure potential difference across it.
- ⚡ The experiment starts with the wire at its full length of 100 centimeters and progressively measures at shorter lengths down to 30 centimeters.
- 💡 Shorter wire lengths can cause the wire to heat up due to increased current, which can alter resistance and affect the experiment's accuracy.
- 📊 Data collected includes voltage and current readings at various wire lengths, which are used to calculate resistance using Ohm's law (V = IR).
- ✅ It's crucial to disconnect the circuit between measurements to prevent the wire from overheating and to maintain accurate resistance readings.
- 📈 The results are plotted as a graph with resistance on the y-axis and length on the x-axis, expected to show a straight line with a positive gradient.
- 🔌 Proper circuit connection and disconnection are emphasized for safety and to ensure the wire's resistance is not altered by continuous current flow.
Q & A
What is the purpose of the experiment described in the script?
-The purpose of the experiment is to investigate how the resistance of a wire changes with its length.
Why is nichrome wire used instead of copper wire in this experiment?
-Nichrome wire is used because it has a higher resistance, which is easier to measure compared to the low resistance of copper wire.
What is the initial length of the nichrome wire used in the experiment?
-The initial length of the nichrome wire used is one meter.
What is the role of the ammeter and voltmeter in the circuit?
-The ammeter is used to measure the current flowing through the wire, while the voltmeter measures the potential difference across the wire.
Why is a double length cable used to connect the ammeter and voltmeter?
-A double length cable is used to ensure there is enough reach to make the connections without struggling, especially when measuring longer lengths of wire.
What is the significance of keeping the wire taut on the meter ruler during the experiment?
-Keeping the wire taut ensures accurate measurement of the wire's length and prevents any slack that could introduce errors into the results.
Why does the experiment stop at 30 centimeters?
-The experiment stops at 30 centimeters because at shorter lengths, the resistance is too small, leading to a large current that causes the wire to heat up, which in turn changes its resistance and affects the experiment's results.
How is the resistance of the wire calculated for each length?
-The resistance for each length is calculated by dividing the potential difference (voltage) by the current, following Ohm's law.
What is the importance of disconnecting the circuit between each reading?
-Disconnecting the circuit between each reading prevents the wire from overheating due to continuous current flow, which could change its resistance and affect the accuracy of the experiment.
What is the expected outcome when plotting resistance against length on a graph?
-The expected outcome is a straight line of best fit with a positive gradient, ideally passing through the origin (0,0), indicating a direct proportionality between resistance and length.
Outlines
🔬 Experiment Setup: Measuring Wire Resistance
The first paragraph describes the setup for an experiment to measure the resistance of a wire, specifically a high-resistance nichrome wire. The experiment involves a series circuit with a battery, an ammeter, and the resistance wire. The wire is stretched along a meter ruler to measure its length accurately. A voltmeter is connected to measure the potential difference across the wire. The experiment starts with a 100-centimeter length and works down to 30 centimeters, as shorter lengths can cause the wire to heat up and alter its resistance, affecting the experiment's accuracy.
📊 Data Collection and Analysis: Resistance vs. Length
The second paragraph details the data collection process and the subsequent analysis. Voltage and current readings are taken at various wire lengths, starting from 100 centimeters down to 30 centimeters. The resistance is calculated using Ohm's law (voltage divided by current) for each length. After all measurements are taken, the power supply is disconnected to prevent overheating. The data is then used to plot a graph of resistance against length, with the expectation that the graph will show a straight line with a positive gradient, ideally passing through the origin, indicating a direct proportionality between resistance and length.
Mindmap
Keywords
💡Resistance
💡Nichrome
💡Meter Ruler
💡Series Circuit
💡Ammeter
💡Voltmeter
💡Ohm's Law
💡Potential Difference
💡Crocodile Clip
💡Graph
💡Overheating
Highlights
Investigating the resistance of a wire, specifically using nichrome due to its high resistance.
Using a meter length of nichrome wire for accurate measurement.
Setting up a series circuit with a battery, ammeter, and resistance wire.
Using a double length cable for connections to ensure reach and avoid measurement errors.
Connecting the voltmeter to measure potential difference across the wire.
Starting measurements at the 100-centimeter mark and working towards shorter lengths.
Avoiding measurements below 30 centimeters to prevent wire heating and resistance change.
Recording a voltage of 4.71 volts and a current of 0.08 amp at 100 centimeters.
Observing a drop in voltage and an increase in current as wire length decreases.
Calculating resistance using Ohm's law by dividing voltage by current.
Disconnecting the circuit between readings to prevent wire heating and ensure accurate resistance measurements.
Plotting a graph of resistance against length to analyze the relationship.
Ideally, the graph should show a straight line with a positive gradient through the origin.
Ensuring the circuit is connected for the shortest time possible to minimize heat-induced resistance changes.
The importance of proper circuit setup and measurement techniques for accurate experimental results.
Transcripts
in this investigation we will be looking
at the resistance of a wire and how that
resistance changes with the length of
the wire now for this experiment we're
not going to be looking at copper wire
because its resistance is too small to
measure easily but a particular high
resistance wire called nichrome so
you'll need a meter length of this wire
take down onto a meter ruler so we can
easily easily measure how long the
length of wire that we're testing is so
first thing to do is to set up the
circuit now we need to be able to
measure both the current and the
potential difference across the wire so
first off I'm going to put the voltmeter
to one side and just build a series
circuit with the battery the ammeter and
the resistance wire we want to test
so first connection battery to ammeter
and then I'm going to connect the
ammeter to one end of the resistance
wire now to do this I'm going to use a
double length cable so that I've got
plenty of reach I'm not struggling at
all to make sure that the whole circuit
is connected when I'm trying to take the
measurements of the longer lengths of
wire and I'm going to just clip on the
crocodile clip at the end on the zero of
the meter and that crocodile clip will
stay there then for the entire
experiment next up at the other end
take the second crocodile clip and I'm
going to clip this on to the 1 meter end
of the meter ruler to start with but
this crocodile clip is going to move
during the course of the experiment so
that we can test different lengths of
wire now I'm going to bend to finish off
by connecting that up to the other
terminal of the battery again using a
double length cable so that I've got
plenty of leeway I'm not struggling for
reach on the Y's at all and I've now got
a series loop from the battery to the
ammeter through the resistance wire and
back to the battery
last thing to do then so that I can get
my measurements of potential difference
is to connect the voltmeter up last two
wires into one terminal of voltmeter and
then I'm just going to connect that into
this junction here and with the last
wire connect to the other terminal of
the voltmeter up to this junction and
that completes the circuit for this
experiment now I'm going to start taking
measurements I'm going to take
measurements starting with the meter end
or 100 centimeter end and work my way in
towards my shorter range I'm going to
stop at 30 centimeters because if you
are testing a short piece of wire the
resistance of such a short piece of wire
is too small the current gets too large
and this means that the wire heats up
and once the wire starts heating up it's
resistance changes and that throws out
the results and ruins the quality of the
experiment okay so starting at the 100
centimeter end first reading I have a
potential difference a voltage of four
point seven one volts and a current of
0.08 amp then all I need to do to test
the next length is unclip red wire here
leave the other one in place and just
clip it on at the 90 centimeter mark on
the ruler do make sure that the piece of
wire again is taut on the meter
otherwise you're going to end up with
more than 90 centimeters of wire and
that would introduce an error to the
quality of your results throw out all of
your readings at 90 centimeters now I
have a a meter reading still of naught
point naught 8 amps but the voltage has
dropped so my current is still 0.08 my
voltage has now dropped to 4
four point six three volts as the
resistance of a short piece of wire slow
really simple now just sliding the
crocodile clip along to 80 centimeters
the voltage reading now drops again to
four point five one volt and the a meter
reading has risen to 0.09 amps
slide the crocodile clip along again to
70 centimeters the volt meter reading
now has dropped again to four point four
one volts the a meter reading has risen
to 0.1 amps
moving on to sixty centimeters and we
get a current of 0.12 amps and a voltage
of four point two six volts so move
along to 50 centimeters we've now got a
voltage reading of four point zero nine
volts and the current of zero point one
four and forty centimeters we have a
voltage of three point eight eight volts
and a current of zero point one six amps
and for the last measurement of thirty
centimeters the current has risen to
zero point two zero amps while the
potential difference has dropped to
three point five four volts all that
follows on there is to calculate for
each length the resistance of the wire
to calculate the resistance for each
length of wire we need to take the two
readings we've got and divide the
potential difference by the current
following Ohm's law that will give us
the resistance at that length and once
we have the resistance at each length of
wire we can then plot a graph of
resistance against length to see how the
relationship between the two as soon as
you have finished taking all of your
measurements most important thing to do
is to disconnect the power supply from
the circuit stop the current flowing
that prevents any overheating it's also
a good idea in between each reading to
disconnect the circuit
so that the wire is not having a current
flowing through it all the time which
leads to more heating which changes the
resistance of the wire so it's important
to make sure that basically the circuit
is connected for the shortest time
possible
so having plotted the resistance on the
y-axis length on the x-axis we draw a
line of best fit through the middle of
those points ideal it should be a
straight line of best fit with a
positive gradient ideally it should go
through the origin through zero zero
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