Resistance of a Wire - GCSE Science Required Practical

Summary

This 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

00:00

🔬 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.

05:02

📊 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.

Keywords

💡Resistance

Resistance in the context of the video refers to the opposition a material offers to the flow of electric current. It is a fundamental concept in physics and is measured in ohms. The video focuses on how resistance varies with the length of a wire, using a nichrome wire to demonstrate this relationship. For example, as the length of the wire increases, so does its resistance, which is a key observation in the experiment.

💡Nichrome

Nichrome is a specific type of wire mentioned in the video that has a high resistance, making it suitable for this experiment. It is an alloy of nickel and chromium, often used in applications where a consistent resistance is needed, such as in heating elements. The video uses nichrome instead of copper because copper's resistance is too low to measure easily, highlighting the importance of material selection in scientific experiments.

💡Meter Ruler

The meter ruler is used in the video to measure the length of the wire accurately. It is a tool that allows for precise measurement, which is crucial for the experiment's accuracy. The script mentions using the meter ruler to ensure that the length of the wire being tested is consistent and measurable, emphasizing the need for precision in scientific measurements.

💡Series Circuit

A series circuit is a configuration where components are connected end-to-end in a single path, as described in the video. This type of circuit is used in the experiment to ensure that the current flows through each component in sequence, including the battery, ammeter, and resistance wire. The setup is essential for measuring the current and potential difference across the wire, illustrating the practical application of series circuits in experimental setups.

💡Ammeter

An ammeter is an instrument used to measure the electric current flowing through a circuit. In the video, it is connected in series with the resistance wire and battery to measure the current. The ammeter reading is crucial for calculating resistance using Ohm's law, as it provides the current value needed alongside the potential difference measured by the voltmeter.

💡Voltmeter

A voltmeter is used to measure the potential difference, or voltage, across two points in an electrical circuit. In the video, it is connected in parallel to the resistance wire to measure the voltage drop across it. This measurement, along with the current reading from the ammeter, allows for the calculation of resistance, demonstrating the voltmeter's role in verifying Ohm's law.

💡Ohm's Law

Ohm's law is a fundamental principle in electrical engineering that states the relationship between voltage (V), current (I), and resistance (R) in an electrical circuit: V = IR. The video script describes using this law to calculate the resistance of the wire at different lengths by dividing the measured voltage by the current. This calculation is central to the experiment's objective of understanding how resistance changes with wire length.

💡Potential Difference

Potential difference, or voltage, is the work needed per unit charge to move electricity through an electric field from one point to another. In the video, the voltmeter is used to measure the potential difference across the resistance wire. As the wire's length changes, so does the potential difference, which is a key variable in the experiment to understand the resistance variation.

💡Crocodile Clip

Crocodile clips are used in the video to connect the wire to the circuit. They are named for their resemblance to a crocodile's mouth and are used for making temporary electrical connections. The script describes how the clips are used to adjust the length of the wire under test, highlighting their utility in manipulating the experimental setup.

💡Graph

A graph is a visual representation of data, used in the video to plot the relationship between resistance and length of the wire. After calculating the resistance for various wire lengths, the data is plotted on a graph with resistance on the y-axis and length on the x-axis. This visual representation helps to analyze the trend and understand the relationship between the two variables, which is a common practice in data analysis and scientific research.

💡Overheating

Overheating refers to the excessive heating of a material, which can occur when a current flows through a wire. In the video, it is mentioned that overheating can change the resistance of the wire, thus affecting the experiment's results. To avoid this, the script advises disconnecting the circuit between measurements to prevent continuous heating, illustrating the importance of controlling variables in scientific experiments.

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