In this investigation you are going to test a variety of materials to find out how they conduct an electrical current. 1.2 Explain the mechanisms of electrical conduction in a range of materials. 1.3 Explain energy changes when an electric current flows X Y A Set up the circuit as shown above, with a cell, switch and ammeter in series with the first test material. Close the switch and measure the current on the ammeter. Record the current in the table below. Record any other observations you make while the current is flowing. Repeat the experiment for different materials. (You may need to change the range setting on the ammeter.) Discussion For each material: Produce a diagram to show the structure of the material at an atomic level and annotate the diagram to show the location of charges. Use your diagram to explain the current observed in the experiment. (AC 1.2) Explain what happens to the chemical energy supplied by the battery when a current flows through the material. (AC 1.3) Task 1b: Practical to investigate the charging and discharging a capacitor In this investigation you are going to find out how resistance affects the rate at which a capacitor discharges. You are provided with a capacitor C, a resistor R, a battery, a voltmeter, a two way switch, connecting wire and a stop watch. Record the values of the capacitance and the resistance. C= R= Construct the circuit as shown in the diagram. Material Current / A Observations Copper Graphite Plastic Deionised water NaCl solution Apply Coulomb's Law to explain movement of charges. 2.2 Analyse the charging / discharging of a capacitor in a DC circuit. 12 Adjust the switch to fully charge the capacitor. Measure the potential difference across the capacitor, V0. Adjust the switch to allow the capacitor to discharge through the resistor and start the stop clock. Measure the potential difference across the capacitor every 10s until the capacitor has almost discharged. Record the readings in the table provided overleaf. Plot a graph of potential difference (V) against time (t). Find the time taken for the potential difference to fall to 0.37 of its initial value. This is known as the time constant of the circuit (). Repeat the experiment with a different resistor. Plot the graph of V against t on the same set of axes as the first graph. (AC 2.2) Analysis and Discussion Use information about the structure of a capacitor to explain why charge accumulates on the plates of the capacitor when the switch is in position 1. Use Coulomb's Law to explain the factors that limit the amount of charge that can be stored in this way. (AC 1.1) Use the graphs to show that for a capacitor discharging through a resistor the time constant, = CR. Explain why the capacitor discharges much more slowly than it charges. (AC 2.2)