This thing starts off by explaining the an interpretation of resistance in an electrical circuit. Learners will then look in ~ the use of resistors. This is a revision of few of the concepts covered in Gr 8 energy and readjust when looking at the Energy transfers within an electrical system (Chapter 2). For basic reference come what learners extended in the vault grade, you can visit the website wherein this contents is located online, and navigate to the relevant grade and chapter.

You are watching: What factors affect the resistance of a conductor

This year, the ide of resistance will certainly be prolonged by looking in ~ the determinants that affect resistance in a resistor, namely:

the type of material of i beg your pardon the conductor is do the thickness the the conductor the length of the conductor the temperature of the conductor

These will certainly be investigated experimentally. Learner must be able to explain the relationships between these factors and the resistance available by the resistor. That is not essential to show experimentally just how temperature affects resistance, yet the principle must still it is in covered. CAPS argues investigating at least one the the other factors. All three investigations have been contained in this workbook so that you have actually the choice as come which one you would like to conduct with your class, or, if time permits, you deserve to conduct all three investigations. 3 hours have been allocated come this section in CAPS, so friend should have time to perform more than among the investigations. In the workbook, they have been presented together three different investigations, but you can additionally perform lock concurrently, or clues a different investigation to different groups. The groups can then report ago to the class on their findings and also you can subsequently summarise the effects on the board.

If you only teach herbal Sciences, it is a great idea to check with the an innovation teachers to see how these 2 curriculums complement each other, especially with regard come electricity. Some of the ideas which could be introduced for the an initial time in natural Sciences, have currently been spanned in the an innovation curriculum. Understanding what learners have currently covered and been presented to will aid make her classes much more efficient and an ext stimulating because that learners.

3.1 What is resistance?

This is contained as one introduction.

3.2 provides of resistors (1 hour)




Activity: beneficial resistance

Recalling, identifying, describing


Activity: make your very own rheostat

Following instructions, predicting, observing, explaining


Activity: to compare a brought about a filament irradiate bulb

Describing, drawing, explaining, comparing


3.3 factors that impact resistance (2 hours)




Investigation: how does the product of the resistor impact the resistance?

Hypothesising, identifying variables, complying with instructions, drawing, observing, describing, analysing, concluding

CAPS suggested

Investigation: how does the thickness of the conductor affect the resistance?

Hypothesising, identify variables, complying with instructions, drawing, observing, describing, analysing, concluding

CAPS suggested

Investigation: how does the size of a conductor influence the resistance of the conductor?

Hypothesising, identifying variables, complying with instructions, drawing, observing, describing, analysing, concluding

CAPS suggested

What is resistance? What perform we use resistors for? go length influence resistance? does temperature influence resistance? does the kind of resistor material impact resistance? walk the thickness that a resistor impact the resistance?
A great way to present this object is come act out the following instance with your learners i m sorry is described in the learner"s book. Friend can even just develop an imaginary field by illustration a square v chalk top top the ground and then a small corridor coming turn off of it. Tell learners to first walk about randomly in the field and also then when you signal (indicating that a potential difference has been applied throughout the wire), they all need to move towards the corridor and get with it. You deserve to make the corridor begin off vast and become narrower to more illustrate exactly how the resistance to their movement rises as the corridor i do not care narrower. This just demonstrates one of the factors influencing resistance (namely the width of the conductor), however can be supplied to introduce the idea of resistance.

We have revised the ide of electrical current and also how electrons relocate within a conducting wire before introducing the idea of resistance in an electric circuit.

Think around your college break time. Every one of the learner are outside on the field, sit in groups and relaxing. Few of you will certainly be moving roughly the field from team to group as friend greet your friends. The school bell rings, signaling the end of break. Friend all get up and start moving toward the institution building. You room all able to relocate easily since there is a an excellent deal of room but what happens as you go into the corridor of the institution building?


Everyone now needs to fit with a narrow corridor. Anyone is trying to obtain to class and also so some learners will bump right into other learners. Together you shot to enter your classroom that becomes also more an overwhelming because the doorway is even narrower than the corridor and also so just one or two learners deserve to pass v at a time.

The activity of the learners is very comparable to the motion of electrons in an electrical conductor. The field offers a very low resistance to the activity of the learners and also so the learners space able to relocate freely. The corridor has a greater resistance to the activity of the learners because less learners have the right to now pass v the corridor than with the field. The great doorway uses the highest resistance together it only allows a few learners with at a time.

How deserve to we use this to highlight electrical resistance? Let"s first revise some concepts about electric current.

Electric charge, or charge, is the physical home of issue that causes it to experience a pressure when near to various other electrically fee matter. There room two varieties of electric charges - positive and negative. Electrons have a an adverse charge and also protons have a confident charge.

An electric current is the rate of charge circulation in a closed, electrical circuit. The electrons in one atom space arranged in the outer room around the main nucleus. In metals, the electrons space able come move freely within the metal. The electrons are not connected with a specific atom in the metal. Us say electrons in a steel are delocalised. Have a look in ~ the adhering to diagram which mirrors this.

We can think that the version of a steel as the positive metal ions in solved positions surrounded by a "sea" that electrons.


Conducting wire in an electric circuit is make of metal. If we supply it with a source of energy and a complete circuit, climate the electrons will all relocate in the same general direction v the cable to the confident terminal that the battery. This movement of electrons per time v a conductor is the electric current.


Resistance in an electrical circuit opposes the passage of electrons. The unit the measurement because that resistance is the ohm, with the price Ω.

The ohm gets its name from the German physicist Georg Simon Ohm, that noticed that the potential difference across a conductor and the electric current are directly proportional (Ohm"s Law).

An electrical conductor is a type of product or object which enables electric fee to pass through it.

You can also remind learner at this point that electric insulators room non-conductors as they execute not allow electric charge with them.

All electric conductors have actually some resistance. Part conducting materials have a details resistance and are provided to include electrical resistance come a circuit. An electric component which adds resistance to a circuit is referred to as a resistor.

Different species of resistors used to include resistance come an electric circuit.

Can you watch that over there are different coloured bands on the resistors? This isn"t just to do them look satisfaction to the eye. The coloured bands space actually a password that tells us the stamin of the resistance the the resistor.

Resistors are electric components and also have a prize to stand for them in an electrical circuit diagram. Do you psychic the symbol from Gr 8? attract it in the space below.

There space two symbols supplied to stand for resistors, however the one most typically used is the the one making use of a block.


top top a microscope level, electrons relocating through the conductor collide (or interact) v the particles of i m sorry the conductor (metal) is made. Once they collide, they transfer kinetic energy. This leader to resistance. The transferred energy causes the resistor to warm up. You have the right to feel this straight if girlfriend touch a cellphone charger as soon as you are charging a mobile - the charger it s okay warm since its circuits have some resistors in them.

Resistors have the right to be used to regulate the current in a circuit. Think earlier to several of the occupational that friend did in Gr 8. If you increase the resistance in a circuit, what wake up to the current? define your answer.

comment on this v your class as they might not have performed these investigate in the ahead grade. Once the resistance in a circuit increases, the present decreases. Adding an ext resistance boosts the opposition to the flow of charge so that is more an overwhelming for charge to relocate through the circuit. Thus there is less present (as current is the rate of circulation of charge). Us say the the existing is inversely proportional to the resistance, meaning as the resistance increases, the present decreases.

Another means in i m sorry we can use resistors is to provide useful power transfers. Carry out you remember looking at power transfers in a mechanism in Gr 8? The input energy start the system and also then gives an output energy. Some of the output energy is helpful to us, and some is wasted energy. For example, a resistor deserve to be used to transfer electric energy into light (light bulb) or into heat (kettle element). Energy is wasted as it is lost to the surroundings. Resistors are provided to provide useful energy transfers.

This task links earlier to the work done in great 8 Energy and also Change. The difference in between "useful" and also "wasted" energy is highlighted again. The learners need to see the resistors have the right to be provided to provide useful energy transfers.

Why carry out we desire to resist the activity of electrons? Resistors deserve to be incredibly useful. Think about a kettle. If friend look within you will view a big metal coil.

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Looking inside a kettle.

This metal coil is the heating element. If you plug in and switch top top the kettle, the facet heats up and also heats the water. The aspect is a huge resistor. As soon as the electrons relocate through the resistor, they release a many of power in overcoming the resistance. This power is transferred to the water in the form of heat. This deliver of power is beneficial to united state as the thermal power is supplied to boil water in the kettle.