# To investigate the factors which may affect the resistance of resistance putty.

Melanie Underwood                                                                                                    Physics Coursework

To investigate the factors which may affect the resistance of resistance putty

Planning

There are three different factors, which may affect the resistance of resistance putty. These three factors are temperature, length and thickness. To investigate the temperature it is very hard to make the temperature go up/down in certain intervals, it’s also hard to connect the connecting wires to the putty itself. If I were investigating the temperature, the putty would have to be placed in a water bath with a Bunsen Burner underneath. If investigating length, it is easier to connect the connecting wires to the putty whilst making sure only one variable is changed i.e. temperature has to stay the same, thickness the same, but only length changes. If investigating the thickness, the shape and length has to stay the same i.e. rounded shape at the end or square, but only the thickness changes. The thickness could either be measured by measuring the circumference or diameter of the end.

For my investigation, I am going to investigate the length factor to see if the resistance of resistance putty changes. This is because it is the easiest factor to change just one variable, whereas with the others it is slightly harder to change just the one variable.

I predict that for my experiment, the longer the length is, the greater the total resistance will be. I predict this because when doing a previous experiment with changing one variable (length) of a piece of resistance wire in a circuit, the total of resistance increased as the wire got longer. This is because when using a rheostat, the current has to flow through a longer length of coil and we see that the current is smaller, showing the resistance is larger. Even though wire is not being used in this investigation, I still think that this idea relates to the resistance of resistance putty.

I also predict my graph will look like this:

I don’t think I will get results which are directly proportional (This is when one of the quantities is doubled, and the other quantity also doubles. E.g. If Resistance is doubled, length would also be doubled).

I also don’t think I will get results which are inversely proportional (This is when one of the quantities is doubled, the other quantity halves. E.g. If length is doubled, the resistance would half). Instead, I think I would get results which are neither of these but have a linear relationship (i.e. both values increase at the same rate.) I also think that even though there is no length of resistance putty in the circuit, there could still be some resistance. This is because connecting wires can carry some resistance in a circuit.

Knowing what resistance is, is very important if an investigation on resistance is being carried out. Therefore, resistance is the ability of a substance to hinder the flow of electricity, a resistor is also related to resistance; it is a device that increases the resistance to an electric current. To calculate resistance, one needs to know the current reading (in Amperes) and the potential difference over the object we are trying to find the resistance of (measured in volts). To work out the resistance from these two values, the formula: -

V = R                (i.e. Potential Difference = Resistance)

I                                   Current flowing

The P.d. is always measured in Volts (V), current flowing in amperes (A) and resistance in ohms (Ω). Along with Ohm’s law there is also Kirchoff’s current and voltage laws. In Kirchoff’s current law, he states that the electric current in amperes, which flows into any junction in an electric circuit, is equal to the current that flows out. This can be seen to be just a statement of conservation of change. Since you do not lose any charge during the flow process around the circuit, the total current in any cross-section of the circuit is the same. This means it doesn’t matter where in a circuit you place an ammeter, as the reading will always be the same.

Kirchoff’s voltage law states that the voltage changes around any closed loop must sum to zero. No matter what path you take through an electric circuit, if you return it to your starting point you must measure the same voltage, constraining the net change around the loop to be zero. Since voltages is electrical potential energy per unit charge, the voltage law can be seen to be a consequence of conservation of energy.

Resistors can be connected in series or parallel. If connected in series, the total amount of resistance in the circuit is the resistance of the resistors added ...