Hard homework questions

Page 6: Q4b You need to find the charge Q by using Q=It. Then use V=W/Q.

Page 7 Q10. This is the circuit described.
But it then says that the voltmeter has a resistance, so we could re-draw the circuit like this:

All you have to do now is find the share of the voltage taken by the parallel combination. You start by working out the combined resistance of the two parallel resistors and go from there.

Units for resistance and conductance.

Resistance is calculated as R=V/I.

You know that the units are OHMS.

However, because R=V/I, we could say that resistance is measured in Volts per Amp (VA-1)

Conductance is calculated as G=I/V.

The units are Siemens.

However, because G=I/V, we could say that conductance is measured in Amps per Volt (AV-1)

If you bear this in mind, you'll be able to do Q1 on page 5. (but note that they use milliAmps per Volt mAV-1)

IV and VI graphs

This is the normal way that we do graphs with voltage on the x-axis and current in the y-axis. Wire A lets a lot of current through with small voltages. We say that it conducts well - it has a big CONDUCTANCE. (or a small resistance). Hence GRADIENT MEANS CONDUCTANCE. This is the old fashioned way of presenting the same information. Notice that the axes are the other way round. Notice that for B, even a large voltage produces only a small current. It has a high resistance. So now GRADIENT MEANS RESISTANCE.

This is our filament bulb graph. Notice that as the voltage increases, the gradient gets less. In other words, it doesn't conduct as well when it gets hot, because resistance increases.

Now look at the filament bulb when the axes get changed around. On this graph, gradient means resistance, so it needs to get steeper to show higher resistance.

YOU NEED TO CAREFULLY LOOK AT THE AXES ON ANY GRAPH AND THINK ABOUT IT. DON'T ASSUME!