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    Can someone explain to me why the resistance of conductors increases when temperature increases and why the resistance of insulators decreases with temperature? In simple terms please thank you!

    Can you also explain the cause of resistance in metals and insulators? In metals, I think it's because the ions in the molecule are moving due to heat which bump into the electrons preventing them from flowing from one side of the metal to the other. And as electrons are the carriers of charge it prevers the flow of current? Can anyone help PLEASE!

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    Can someone explain to me why the resistance of conductors increases when temperature increases and why the resistance of insulators decreases with temperature? In simple terms please thank you!
    The reason is that 2 different effects are going on. In a conductor, electrons are freely available and can readily move around, i.e. excess heat is not needed to get them moving. However, excess heat causes the atoms that make up the conductor to vibrate more. This means that it is harder for electrons to move through the conductor, as the more the atoms vibrate, the more they get in the way of the electrons.

    In insulators, the electrons are not readily available (as they are tightly bound to their individual atoms). Extra heat provides the energy to rip these electrons away from their atoms, so they can become conduction electrons. The number of conduction electrons therefore increases as the temperature increases, meaning that the electrical conductance of the insulator will increase with temperature (and hence the resistance decreases, as the two are inversely proportional). The extra heat will also make the lattice vibrate more in an insulator, but the extra difficulty to motion this causes for the electrons is more than offset by the increase in the number of conduction electrons available.

    Can you also explain the cause of resistance in metals and insulators? In metals, I think it's because the ions in the molecule are moving due to heat which bump into the electrons preventing them from flowing from one side of the metal to the other. And as electrons are the carriers of charge it prevers the flow of current? Can anyone help PLEASE!
    Pretty much right in metals - the vibrating lattice gets in the way of electrons and scatters them, so impedes their progress through the lattice and hence causes resistance. Resistance can be thought of in this context as the changing of the direction of electrons as they move.

    In insulators, the cause of resistance is that the electrons are bound so tightly to their parent atoms that it takes loads of energy to get them moving through the metal - here resistance can be though of as resistance to motion.
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    Basically as the elctrons move in a metal, they bump into things. Now it can be shown that I = naVe where v is the average velocity of electrons and i is the current. If the electrons bump into a lot of things then they have a slower velocity, and thus less current flows (and if this is the case from v = IR we can say R increases if v is constant). Now when we increase the temperature of a material the bits, protons and whatnot, vibrate faster making it harder for electrons to move through the material and they move slower.

    I hope that helps, im pretty poor at explaining things
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    Resitance increases with tempreture in conductors because the particles have more energy and so are moving more, increasing the liklihood of collisions between the electrons and metal ions

    Think of current as being the net overall movement of electrons- if they're colliding more, the current will decrease.
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    (Original post by spread_logic_not_hate)
    The reason is that 2 different effects are going on. In a conductor, electrons are freely available and can readily move around, i.e. excess heat is not needed to get them moving. However, excess heat causes the atoms that make up the conductor to vibrate more. This means that it is harder for electrons to move through the conductor, as the more the atoms vibrate, the more they get in the way of the electrons.

    In insulators, the electrons are not readily available (as they are tightly bound to their individual atoms). Extra heat provides the energy to rip these electrons away from their atoms, so they can become conduction electrons. The number of conduction electrons therefore increases as the temperature increases, meaning that the electrical conductance of the insulator will increase with temperature (and hence the resistance decreases, as the two are inversely proportional). The extra heat will also make the lattice vibrate more in an insulator, but the extra difficulty to motion this causes for the electrons is more than offset by the increase in the number of conduction electrons available.



    Pretty much right in metals - the vibrating lattice gets in the way of electrons and scatters them, so impedes their progress through the lattice and hence causes resistance. Resistance can be thought of in this context as the changing of the direction of electrons as they move.

    In insulators, the cause of resistance is that the electrons are bound so tightly to their parent atoms that it takes loads of energy to get them moving through the metal - here resistance can be though of as resistance to motion.
    WOW! thank you so much you've helped loads much better than WIKI! Defo +ve rep as you're so good can I ask you some more questions....
    For starters, why does an increase in cross-sectional area cause a decrease in resistance, and an increase in length causes an increase in resistance?
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    For starters, why does an increase in cross-sectional area cause a decrease in resistance, and an increase in length causes an increase in resistance?
    Increase in cross-sectional area implies that there is more space for the electrons to flow along the material, meaning they'll bump into each other less. This means that their flow will be less impeded, i.e. the resistance will be lower.

    An increase in length increases resistance simply as it puts more atoms in the way of the electrons.

    Think of it like this. Imagine electrons are balls and the wire they travel through is a hollow tube. If you dropped a load of balls down a narrow tube, they'd all get stuck and take ages to get out as they would all bump into each other. (i.e the resistance to their motion is high). If you made the tube really wide (by increasing its cross sectional area), they could all fall down together and would get out a lot faster. (i.e. their resistance to motion is low)

    If you make the tube longer, it takes longer for the balls to get to the other end and there is more chance that as they do so they will hit into each other. (i.e. resistance to motion increases again).

    Hope that analogy makes it a bit clearer!
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    (Original post by SmileyGurl13)
    why does an increase in cross-sectional area cause a decrease in resistance
    1st. It causes a decrease in the measured resistance of the wire in the circuit. This is because the current through the wire will increase for the same applied voltage.
    Why?
    The current is a result of a) the (average) drift velocity of electrons (charge) through the wire and b) the quantity of charge flowing per second.
    I.E. The more available electrons you have, and the faster they flow, the greater the current.
    A greater cross-section area increases the number of available charges flowing past a given point per second. And therefore increases the current.
    The drift velocity of the electrons is the same for the same applied pd. So you have effectively increased the current without increasing the pd. This is why the resistance is less.
    and an increase in length causes an increase in resistance?
    If you increase the length of the wire, keeping the applied pd between its ends constant, you reduce the strength of the electric field applied to the electrons. (Electric field strength depends on the potential gradient). This has the effect of decreasing their drift velocity through the wire. (They are accelerated by the applied pd.)
    This in turn means you get fewer electrons passing a point per second.
    Fewer charges per second means a smaller current.
    A smaller current for the same applied pd means that the measured resistance is greater.

    By the way, the connection between this and the answer to your earlier question about the effect of temperature, is that increasing the temperature of the conductor increases the number of collisions the electrons make with the metal atoms. This has the effect of reducing the average drift velocity of the electrons. And for the same reason as I mentioned above, doing this reduces the current in the wire.
 
 
 
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